I rescued this early 80s Fisher Model MC-3020 Stereo from our next door neighbor's garbage. Originally, its was his mother's and had been stored in her garage for many years. It came into my neighbor's possession when his mother passed away. The MC-3020 was known as an Integrated Component System, and incorporates a AM/FM Stereo Receiver, Stereo Cassette Player/Recorder, and a BSR made
Upon initial power up, I found that my garbaged picked MC-3020 had the following problems:
The first step is to completely disassemble the MC-3020. I started by removing the screws circled in red, these screws hold the chassis in place.
You must remove both the cassette player and turntable assemblies before removing the chassis. Four screws, circled in the picture below, hold the cassette player to the wooden cabinet.
You must detach this AC Choke from the chassis, using the screws circled in red, before removing the cassette deck assembly.
Carefully lift up the cassette player assembly and then disconnect all wiring to the the chassis. The cassette player assembly is then free and clear of the wooden cabinet and can be set aside for later servicing.
The chassis must be slid as far forward until an obstruction is felt. This will allow you to reach inside from the front to free the turntable from the wooden cabinet.
The turntable assembly is held in place on the underside by two clips, positioned diagonally from each other. You must reach in from the front of the wooden cabinet to remove them.
Disconnect the right and left Tone Arm audio connections from the back of the wooden cabinet, noting their color and position.
The turnable assembly can be removed, once the remaining electrical connection has been disconnected. At this point, the chassis can be remove from the wooden cabinet by pulling it forward.
Once removed from the wooden cabinet, I recommend propping up the turnable assembly on several 2x4 wood blocks, so that the mechanical undercarriage is not bearing the weight.
Chassis Switch and Control Cleaning
Upon initial testing, I discovered that the right audio output was not working on my MC-3020, I suspected the culprit was a dirty switch or mechanical control. As such, I decided to spray contact cleaner inside every mechanical control in the chassis then put them through the motion several times to clean up the contacts and the resistive elements the contacts may touch.
First I sprayed one Function switch deck.......
and the other Function switch deck.
Both decks of the Volume control.
And inside the remaining Balance, Treble, Bass, and the Recording Level controls. In addition, I sprayed contact cleaner inside the Tape Monitor, Loudness, Mode and Power buttons. Here is a picture of me spraying contact cleaner inside the Tape Monitor button. Don't forget to exercise the control after spraying contact cleaner into it!
Tuner Dial Lubrication
Like many stereos of the era, the MC-3020 uses a dial cord and pulleys to connect the Tuning Knob, Tuning Variable Capacitor, and Analog Dial Frequency Indicator together. While the chassis is out, it is a good idea to lubricate the shafts of each dial cord pulley . I use Labelle 107 Oil as it is safe on plastics and I have it around for my model train hobby.
Chassis Indicator Light Cleaning
The MC-3020 uses many incandescent bulbs for back lighting and for indicators. As the chassis is apart, it is a good idea to clean them using Windex and a lint free chamois.
Here is a "before" picture of the Tuner Dial Backlight bulbs, notice their dirty glass envelopes.
Here is a picture of the Tuner Dial Backlight bulbs after cleaning. Notice the difference?
In addition, I recommend cleaning the Tuner Dial Backlight enclosure as well.
With the Tuner Dial Backlight enclosure removed, you can access the back of the Tuner Dial Bezel for cleaning.
The Record and Stereo indicators use small light bulbs. I recommend cleaning these as well.
I recommend cleaning the Record and Stereo indicators light bulb enclosures as well using a Q-tip moistened in Windex.
The Recording Level Indicator meters can be removed from the chassis, allowing you to clean their meter faces.
Chassis Electrolytic Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 40 year old electrolytic capacitors like the ones in the MC-3020!
Electrolytic capacitors should be replaced with one of similar capacitance and equal or above Voltage rating. These type of capacitors are also polarized so make sure you observe the polarity of the capacitor to be replaced and install new the same way.
I check each replacement capacitor with my trusty GM328 Multi-Function Tester before installation.
I replaced electrolytic capacitors on one printed circuit board at a time in the chassis. In this case I am replacing the capacitors on the "AIN Power" board. I mark the replacement capacitors with a permanent black marker line on top to indicate they have been replaced as sometimes the original and replacement capacitors look very similar. The light blue one circled in this picture still needs to be replaced.
In many cases, new electrolytic capacitors of same capacitance and working voltage are much smaller that their older counterparts.
After the electrolytic capacitors on a printed circuit board are replaced, I test the chassis by connecting speakers, antennas for both AM and FM, then connect power and turn it on. You do not need to the connect the cassette deck or turnable assemblies for this step. Just turn the mode switch to AM or FM only. Notice that I did not replace one of the large capacitors on the AIN Power board. I will have to come back to replacing this capacitor as I did not have one with the proper capacitance and working voltage in stock. One of the first things I noticed was that sound was now coming from both speakers now. Looks like applying contact cleaner to the mechanical switches and controls in an earlier step resolved my right audio output problem.
As mentioned, the turntable platter and tone arm would not move at all in Manual or Auto modes when the MC-3020 was powered on. In addition, I could not remove the spindle or turn the platter by hand. My experience with turntables has shown me that the culprit is old grease that has decomposed into a glue like gunk. Your best weapon against grease turned gunk is heat. When applying heat to the spindle make sure you do not melt the rubber mat that covers the platter.
The platter bearing was seized as well. After removing the e-clip. I took the solder tip out of my 40 Watt Weller soldering iron then used the soldering iron to heat up the bearing, and by proxy the grease in it, until I could lift the platter off of its shaft.
After reapplying heat several times, the platter finally came off. This exposed the idler wheel, used to control the platter speed, the left and right tone arm audio connections to the chassis, and the tone arm gear.
I had to also apply heat to the tone arm gear using a solder gun, in order to thin the old grease, allowing it to be removed from the plinth or base.
Here's a picture of me using a Q-tip to remove the old grease from the platter shaft.
Time to lube things up on the top side of the plinth. After cleaning out the old grease, I applied Labelle 106 PTFE grease to the platter bearing before assembly. Labelle 106 is safe on plastics and I always have a tube of it due to my model train hobby.
The platter bearing sits at the base of the shaft.
Time to grease the track on the tone arm gear.
Time to oil the remaining components on the top side of the plinth. I put a drop of oil on the platter, idler, and tone arm gear shafts.
It is a good idea to put some grease on the gear at the base of the platter, before assembly.
An e-clip on the platter's shaft holds it in place. As you can see, I accidentally melted the platter's rubber mat during disassembly.
The aluminum BSR logo center just slips in and under the center of the rubber mat.
The aluminum outer ring that graces the platter's rubber mat fell off during disassembly. I had to scrape off the old adhesive then remove the residue with denatured alcohol.
I put E6000 all purpose adhesive on the back side of the aluminum outer ring.
Then I positioned the aluminum outer ring in place on the platter's rubber mat, and held it down with five D batteries, in order to help it adhere.
The back side of the plinth, or base of the turntable, has many mechanical joints that need to be oiled as well. I oiled each and every joint then ensured they moved freely.
The back side of the plinth also contains many gears that need to be greased. First, I cleaned off the old grease using a Q-tip dipped in denatured alcohol. Then, I applied new PFTE grease.
I Applied a drop of oil to the spindle and made sure all parts of it moved freely.
Time to test the turntable assembly. I made the proper electrical connections between the chassis and turntable assembly, then propped it up on several 2x4 blocks, making sure that the mechanical parts on the underside of the plinth were not obstructed.
After lubricating the turntable assembly, I had a curious issue in auto mode where the timing was off and the record would drop after the tone arm was already in position. I spent many evenings troubleshooting this issue, thinking that I either bent or assembled something wrong. On a whim, I decided to turn the spindle 180 degrees in its center mount of the platter. Like magic, everything started to work as expected with the record dropping first, followed by the tone arm moving into position. The spindle mount in the platter shaft has a notch, the spindle record dropping mechanism must align with this notch.
Cassette Deck Repair
The adhesive that held the cassette keys in place had grown brittle through the years. When I pressed the Stop key the Play key would launch into the air. I used E1000 adhesive to glue all keys back onto their metal mounts.
In order to get at the cassette desk mechanism and the electrolytic capacitors on the printed circuit board, you must remove it from its mounts. Three screws, circled in red, hold the printed circuit board to the cassette deck chassis.
I replaced all of the electrolytic capacitors on the printed circuit board with new.
There is also one electrolytic capacitor, circled in red, across the motor leads that needs to be replaced.
There is a switch on the printed circuit board that is triggered by the cassette keys, via its mechanism. Access to the contacts within the switch can be obtained through its end. I recommend spraying some contact cleaner into it, then exercising the switch manually, so that the contacts are properly cleaned.
In the cassette deck chassis, I put a drop of oil on all pulley shafts and then made sure each pulley spun freely.
I applied PFTE grease to any metal slides, after the old grease was cleaned away with a Q-Tip dipped in denatured alcohol.
The initial issue was that the cassette player played the cassette at slower than normal speed and the cassette counter did not work. I had determined this was due to deteriorated drive belts. I replaced both of them with new drive belts I had on hand. I purchase drive belt kits on eBay that contain a variety of lengths. Most of these drive belt kits come from China so it takes awhile to be delivered to my home in the United States. Purchasing a drive belt kit from China is a lot cheaper than purchasing the individual belts from an electronic parts distributor.
Time to attached the printed circuit board to the cassette deck chassis using three screws circled in the picture below.
Like the turntable assembly, I also test the cassette deck assembly out of the cabinet by connecting the proper electrical connections to the chassis, propping it up on 2x4 blocks then powering on the chassis. The cassette deck works a lot better now that the drive belts have been replaced.
I treated the MC-3020's wooden cabinet, inside and out, to a coat of lemon oil. This is the best time to do it, with all of the electronics removed.
I then buffed the veneer with a lint free chamois.
Next, the chassis was reinserted part-way into the wooden cabinet from the front.
I placed the turntable assembly in place on top of the wooden cabinet, then connected the power connection to the chassis.
You must attach the turntable assembly's tone arm audio connections from the opening in the back of the wooden cabinet.
The two clips that hold the turntable assembly to the wooden cabinet can then be installed.
Time to install the cassette deck. First, I fastened the AC Choke to the chassis with two screws.
Then, I installed the electrical connector that connects the cassette deck assembly to the chassis.
The cassette deck assembly was once again fastened to the wooden cabinet with four screws circled below.
I noticed the cassette deck was running too fast after assembly. I drilled an access hole that allows me to use a small jewels screwdriver to adjust the cassette deck's speed easily from the outside while it is in play mode.
Finally, I replaced the screws that hold the chassis in place.
Getting this vintage Fisher MC-3020 sure required a lot of work! Actually, it is not work if you really enjoy what you're doing. I thoroughly enjoyed getting this vintage integrated component system up and running again. As you can see, it has a place in my "wall of stereos". I will enjoy listening to cassettes and records being play on it while I work on other projects.
My rebuilt Fisher MC-3020 Stereo in action!
I am continuing with the Chinese radio builds. This time, I will be building the Sheja JH-188 radio kit.
About the Sheja JH-188 Radio
The Sheja JH-188 is an FM only digital mono receiver kit that is commonly found on sites such as Amazon, eBay, Banggood, and Alibaba e-commerce web sites. I purchased mine from eBay for $7.69.
It is built around the CD9088 integrated circuit. The CD9088 is a Chinese clone of the TDA7088T, which was developed by Philips Corporation in the early 1990s.
The TDA7088T, and Chinese CD9088 clone, is a mono FM integrated circuit intended for use in battery operated pocket radios. With the CD9088, no specialized parts such as IF coils or ceramic filters are required, making the parts count built around this integrated circuit low. It has builtin tuning capability if used with an external Varicap BB910 diode. The CD9088 has builtin FM station scan and reset functions. In addition, it has all the necessary stages to process RF input from the antenna to audio output. The CD9088 can be operated with as little as 1.8 Volts DC.
SHEJA JH-188 Circuit Theory
Unfortunately, my JH-188 didn't come with assembly instructions or a schematic. If I would have inventoried this kit upon arrival, I would have noticed the missing assembly/schematic documentation. I was, however, able to find a picture of a schematic on a listing in Alibaba, and included it below. Note: The bottom schematic is an extension of the top one.
Based on my years of electronic experience, I'll try to extrapolate what the discrete components do in this circuit.
C3 - Possibly used to debounce scan reset switch SW2.
C5 - Used to debounce scan switch SW1.
BB910 and L1 - Varicap diode and coil used for the LC tank circuit used for tuning.
C4 - Decoupling or Bypass capacitor, shunts noise caused by other circuit elements to ground.
CD9088 - Integrated circuit used to convert a Radio Frequency(RF) modulated signal to Audio Frequency(AF).
SW3 and LH2 - Built in flashlight circuit.
SW2 - Switch clears all radio stations from memory.
SW1 - Switch used for radio station scan.
PL1 - Audio jack for ear buds. The ear bud wiring is also used as an antenna.
KW1A/B - Audio volume control and main radio power switch.
Q1 - Transistor used to amplify audio signal.
L2 - Possible RF choke, preventing Radio Frequency (RF) signal from entering the audio amplifier stage.
My JH-188 came in an international mail envelope, direct from mainland China. The mail envelope contained a plastic bag with all of the radio's discrete components.
It is important to inventory all parts, prior to starting the assembly process. Immediately reach out to the vendor if any parts are missing. If I had taken my own advice, I would have noticed that assembly instructions and schematic documentation were missing. I use an old plastic food container that contained a salad mix to contain all of the radio's parts so they don't get lost. A mistake in this picture is that I should have stuck the CD9088 integrated circuit and transistor, circled below, in anti-static foam to protect them from damage. You can wrap these components in tin foil if anti-static foam is unavailable. Granted, the supplier did not protect these components by sticking these component's metal leads into anti-static foam, but it is a good practice to get into.
You will need a soldering iron with accurate temperature control and an ultra fine tip, in order to solder the surface mount CD9088 integrated circuit to the printed circuit board. I use the ZENY 862D+, which is a soldering / hot air surface mount rework station, available from many e-commerce vendors.
First, I soldered the surface mount CD9088 integrated circuit to the foil side of the printed circuit board. I started with this component as it was the hardest component to solder in place. It is easier to mount when no other components are already soldered to the printed circuit board.
I then tested all other components, using the Mega 328 Component Tester, before soldering to the printed circuit board. The Mega 328 can test resistors, capacitors, inductors, transistors, and diodes. It cannot, however, test integrated circuits such as the CD9088. I find that these inexpensive radio kits often have discrete components that are either out of tolerance of just simply defective. I replaced any defective or out of tolerance components with spare parts I had on hand.
Next, I soldered all ceramic capacitors and inductors in place. The rest of the components are of the thru-hole type, where the component is inserted from the component side and soldered on the foil side.
I then soldered the single resistor in place.
Next, I soldered the transistor and Varicap diode in place. These components are polarized, meaning they are have to be installed in the proper direction.
All three switches were then soldered in place.
The audio jack, volume control/power switch, and the incandescent light bulb were soldered in place. I placed plastic insulators around leads to the light bulb.
Finally, the wires that connect to the batteries were soldered to the foil side of the printed circuit board.
It is important to test the printed circuit board assembly before mounting it into the radio's case. I connected two AAA batteries to the power connection leads and the supplied ear buds to the audio jack. I then turned the volume control clockwise until I heard the click of the power switch then adjusted the volume control to mid point. Push the SW3 button should turn on the light bulb. Push SW2 should reset scan and then push the SW1 scan button until you hear a radio station. If you don't hear a radio station, check component placement and orientation.
Defluxing the circuit board
Solder contains flux, an agent which aids in the soldering process, but leaves a sticky brown residue behind. Before mounting the printed circuit board in the radio's case, I spray defluxer on the foil side, use a tooth brush to free any stubborn flux, then blow it off with compressed air to remove any residue and to completely dry it.
Look how clean the foil side of the printed circuit board looks after defluxing. At this point, I also soldered the battery connectors to the end of the wires. The spring terminal goes on the black wire while the plate terminal goes on the white one.
Place the radio's front cover face down on a smooth surface and then install the Light, Reset, and Scan buttons.
With the radio's front cover still face down, place the printed circuit board foil side up in the top area of the radio case. Route the wires inside the case so they don't get crimped when the back cover is installed. Install the AAA battery terminals into the battery compartment. The battery terminals just slide in place into the provided slots.
Install the back cover and belt clip, secure with the single provided Philips head screw.
Now turn the radio over and install the silver plastic plate labeled "SHEJA JH-188" it just clips in place.
The knob for the power switch/volume control installs with a single Philips screw in the center. The knob is installed correctly if you hear the click of the power switch opening its contact when at the 8 O'clock position.
A chrome plastic cover clips in place over the top of the screw hole of the power switch/volume control knob.
Place two AAA batteries into the battery compartment then install the battery cover over it.
Plug the supplied ear buds into the audio jack. Turn the volume control knob clockwise until you hear a click of the power switch then move until about mid point. Click on the Reset button, then click the scan button several times until you hear a station. Your radio is now complete!
Station Reception Issue
I noticed that during the testing phase I was picking up a lot more stations than after final assembly. I had determined that I was touching the positive battery lead during testing and my body was acting like a natural antenna. In order to improve radio reception, I connected a 2 ft long blue wire to the positive battery connection then routed the antenna through a small hole I drilled at the bottom of the radio cover.
Below is a picture of the finished SHEJA JH-188. At a price point of under $8, the JH-188 is a great little kit for a hobbyist or a STEM program. It can be used to teach soldering and assembly skills. However, because the JH-188 performs all signal processing using a single integrated circuit, this kit really does teach radio principals. In addition, the JH-188, even with the addition of an external antenna, lacks the sensitivity of most standard FM radios. The low sensitivity of JH-188 only make it suitable for serious radio listening in metropolitan areas were strong radio signals are present.
Today on Radio Boat Anchor, I am going to build the HX-6B Chinese Radio Kit, otherwise known as "the little blue one" by many electronic hobbyists. This kit can usually be found for a few dollars on many e-commerce sites such as Amazon, eBay, Banggood, and Alibaba. I purchased my HX-6B on a "buy it now" auction for $4.59. It shipped directly from China and three weeks later it arrived with my mail.
About the HX-6B Radio
The HX-6B is of standard Superheterodyne or "Superhet" radio receiver design. The Superhet radio design was invented by Edward Armstrong, an Electrical Engineer from the United States, in 1918. It has been used widely in analog AM and FM radio receivers for most of the 20th century until it was supplanted by SDR (Software Defined Radio) in which all single processing is done through code on a one or more integrated circuits. The HX-6B would make a great kit for an educational STEM program as it has all of the building blocks of a basic AM radio receiver. This kit is great for education purposes but will probably lack sensitivity as most AM radios of the Superhet type have two IF (Intermediate Frequency) stages where this kit is only designed with one IF stage. Station reception may not be a problem if you live in a metropolitan area were AM station signal strength is strong.
HX-6B Circuit Theory
The instructions you get with the HX-6B radio kit is primarily in Chinese. However, the schematic and parts list in the instructions are printed in english. In addition, the component side of the included printed circuit board has english destinations for the components. You can easily assemble this kit without the need to read Chinese. All of the circuit theory is written in Chinese, so I am going to extrapolate the circuit theory of the HX-6B, based on my 30 years of electronic experience.
The HX-6B radio kit comes in a clear plastic wrapper. All of the components, including printed circuit board and instructions, are housed in the blue plastic shell of the AM radio.
As mentioned, the instructions are primary in Chinese. However, the schematic and parts lists are in English.
It's a good idea to inventory an electronic kit, such as the HX-6B Radio Kit, before assembly. Make sure all required parts are present and accounted for, before assembly. If any parts are missing, reach out to the vendor, before starting the assembly process, to acquire any missing parts.
I like to put all small discrete parts in a plastic container before assembly. That way they are all contained and it is less likely that I might lose one.
When assembling radio kits, I usually do it in a certain order. First, I solder the resistors to the printed circuit board. Before soldering a resistor to the printed circuit board, I check its resistance value with my Mega 328 component tester. This handy device can check resistor, capacitors, diodes, transistors, and inductors. I often find resistor, capacitors, and inductors either defective or out of tolerance in these little kits. I don't believe they use "top shelf" components. I replace any components that are either defective or out of tolerance.
I solder each resistor, one at a time, to printed circuit board. This is a fun activity and I am in no real hurry.
Once a component is soldered to the printed circuit board, I cross it off of the parts list.
Finally, all of the resistors have been installed in the printed circuit board.
Next, I install the ceramic disk capacitors. Checking each one with my Mega 328 component tester before soldering to the printed circuit board.
Time to install the electrolytic capacitors. Once verified with the component tester, I solder them to the printed circuit board. Electrolytic capacitors are polarized. The negative lead side is denoted on the printed circuit board by a side half of the circle colored in white.
There are three types of NPN transistors included in this kit:
As with other components, I check each one with my component tester before soldering to the printed circuit board. Note, transistors have three different connections, Collector, Base, and Emitter. It is important that you install the proper transistor into the proper holes in the printed circuit board. The locations are labeled on the component side. In addition, you must install them in the proper orientation. You must match the flat side of the transistor with the flat side of the label printed on the component side of the printed circuit board. See areas circled in the picture below:
All of the transistors are now installed.
I then installed the 5K potentiometer with built in power switch. This is labeled RP in the schematic and it will serve as the volume control. There was no way to test the potentiometer with my component tester. I just checked with my VOM (Volt-Ohm-Meter) that it measured 5K Ohms between the two outer leads of the potentiometer. You should see the resistance change from 0 to 5K Ohms or 5K Ohms to 0 if you place the meter leads between one of the outside leads and the center lead.
Next, I installed the audio transformer. I did some resistance checks with my VOM meter to determine if there were three windings, two should have a lower resistance while the third has more windings and should be slightly higher in resistance. The audio transformer must be installed into into the printed circuit board in the right orientation. If you look closely, there is a little raised bump on the bobbin of the transformer, this should line up with the white dot on the component side of the printed circuit board. See areas circled in the picture below:
The audio transformer is installed in the corner of the printed circuit board. In addition, I installed the oscillator coil and the first and second IF transformers. The oscillator, first, and second IF transformers slugs are color coded. You must install them in the proper locations.
T2: Red Slug (Oscillator Coil)
T3: White Slug (First IF Transformer)
T4: Black Slug (Second IF Transformer)
Time to install the audio jack, circled in the upper left-hand corner.
The next step is to install the variable capacitor, used for tuning, to the printed circuit board. The mounting screws used for the variable capacitor are also used to hold the nylon loopstick antenna mount in place.
The two screws provided secures both the loopstick antenna mount and the variable capacitor to the printed circuit board. You will need to solder the three variable capacitor connections to the printed circuit board.
The HX-6B has a Red LED (Light Emitting Diode) power indicator, circled in the picture below. It must be routed though the hole in the printed circuit board from the component to the foil side.
The LED is polarized, the flat side of the component corresponds to the side the arrow points to on the printed circuit board.
The loop stick antenna consists of two windings on a ferrite rod. The windings act like a step-up RF transformer. It is important to connect the wires to the right connections on the printed circuit board. As you can see from the picture below taken from the instructions, connections a and b connect to 100 wire turns while connections c and d are only 10 wire turns. It is easy to identify a and b connections using a VOM (Volt-Ohm-Meter) as the resistance between these connections are higher than between connections c and d.
The easiest way to make the proper connections from the printed circuit board to the windings is to lay it out as shown below.
Once all of the connections to the windings are made, it is time to slide the cardboard tube that secures the windings over the ferrite rod. Next, attach the ferrite rod to the printed circuit board using the nylon loopstick antenna mount. I also attached the dial to both the volume control and the turning capacitor, so that the radio is ready for alignment.
There are several places on the printed circuit board foil side that have broken traces. This is intentional so as to allow current checks of different stages of the radio. My recommendations is to just put a solder bridge across them as I found the current ratings listed in the schematic to be inaccurate. If you don't bridge these connections with solder, the radio will not work!
Time to attach the two provided blacks wires between the printed circuit board and the speaker. The yellow wire to the +3V point and the blue wire to the -3V point. I circled the points in red, on the sparsely populated component side of the printed circuit board, to show you where to make the connections.
On the ends of the yellow and blue wires, you must solder the battery contacts.
Soldering leaves sticky flux residue on the foil side of the printed circuit board. I spray flux remover on the foil side then use an old tooth brush to loosen the flux. I then use compressed air to blow away the flux residue and to dry the board.
I found it easier to assemble the HX-6B radio in its case before performing alignment activities. Double-check the tightness of the screw that holds the dial to the tuning capacitor.
Place the tuning indicator sticker over the tuning dial. I recommend temporality placing the printed circuit board into the radio enclosure then rotating the tuning dial back and forth so that you can determine the proper dial indicator sticker placement.
Next assembly steps:
Install the batteries, the HX-6B radio is now ready for alignment!
You must align a Superheterodyne receiver, in order to get maximum sensitivity and selectivity, and so that the tuning indicator indicates the correct station when being tuned.
Note: Do not use a regular screwdriver with a metal shaft to adjust transformer slugs and trimmer. It will skew your adjustment. It is best to use a non-metallic radio/TV alignment tool.
Note: If an RF Generator is not available, satisfactory results can be obtained by tuning into stations on the low and high end of the radio dial.
Here are the steps to align the HX-6B radio:
In order to further maximize the sensitivity of the HX-6B, you must adjust the antenna trimmer and loop stick antenna.
Below is a picture of the finished HX-6B. Simply install the back cover after the alignment process. At a price point of under $5, the HX-6B is a great little kit for a hobbyist or a STEM program. It can be used to teach basic radio principals, soldering, and assembly skills. However, with its only single IF stage, it lacks the sensitivity of most standard AM radios. The single IF stage makes the HX-6B only suitable for serious radio listening in metropolitan areas were strong radio signals are present.
The HX-6B in action
In addition to restoring antique radios, I also service household electrical and electronic devices. Recently, I serviced my Magnavox LCD Television, it needed an 8 pin surface mount EEPROM replaced and I didn't have the right tools to replace it. That is when I decided to invest in a SMD (Surface Mount Device) Rework Soldering Station.
The Zeny F2C 2in1 862d+ SMD Rework Soldering Station
The Zeny F2C 2in1 862d+ SMD Rework Soldering Station at the time of this writing was the cheapest combo hot air gun and soldering rework station on Amazon. At the time of purchase the price was $53.88. You could pay in excess of several thousand dollars for a good SMD rework soldering station and it might be worth it if you serviced printed circuit boards with SMD mounted components on a daily basis. I chose the inexpensive Zeny F2C 2in1 862d+ SMD Rework Soldering Station because as a hobbyist I rework printed circuit boards with SMD components on an infrequent basis. The Zeny F2C 2in1 862d+ SMD Rework Soldering Station boasts the following features:
There is a person who claims you can add a jumper inside this workstation to change it to display in Fahrenheit. I will include the link to this later in this blog.
Zeny F2C 2in1 862d+ SMD Rework Soldering Station comes in an individual box only slightly bigger than the rework solder station itself.
This rework solder station comes with an instruction manual, four hot air gun tips of various sizes, six soldering iron tips of various sizes, some sort of tool with wire ends that I am not sure what it is used for, and the manual. The manual attempts to instruct you on the operation of Zeny F2C 2in1 862d+ SMD Rework Soldering Station. In my opinion, you're better off watching YouTube videos covering operation of this rework solder station. I think you will find them more useful.
Top view of the rework solder station before I lift if out of its box. The black cable to the right is attached to the hot air gun. Unlike the soldering iron, the hot air gun is permanently connected to the rework solder station. There is not connector that will allow you to detach it.
Here are all the discrete parts in the package. The solder iron stand (blue rectangular object and to the right) is supposed to include a tip cleaning sponge. It is noticeably missing. The hot air gun holder (black plastic piece in the center) needs to be mounted to the rework solder station cabinet before operation. The rework solder station senses when the hot air gun is in the cradle and turns off the heating element, leaving the fan on until it has sufficiently cooled.
Quality Control Check
I like to perform a quality control check on dubious branded electronic equipment from China before initial operation. This equipment is typically well designed but hastily assembled. The first step is to remove the machine screws on both sides that holds the cover in place.
The company "ZENY" that assemble this rework workstation uses some sort of red adhesive to keep the wire connectors firmly attached to the main printed circuit board.
During assembly, they never applied heat to the heat shrink tubing that covers the high voltage AC connections.
This was an easy fix.
I didn't like how they soldered the two ground connections together. They soldered the second ground connection to the first in order to save a lug.
I fished out another solder lug from my junk drawer then soldered the second ground connection to it. I then fastened it back down using one of the screws that holds the step-down transformer in place.
There were no other issues with my rework solder station. I went ahead and reattached the cover then installed the hot air gun holder.
This is how the holder looks with the hot air gun in place.
Some buyers complained that the ceramic heating element in the soldering iron did not make good contact with the solder tip, causing poor thermal heat transfer, this was not the case with the solder iron that was included with my rework solder station.
The soldering iron connects to the rework workstation with a screw on connector and can be easily replaced.
I like to perform an electrical test on dubious branded electronic equipment from China before initial operation. The first checks was to measure AC Volts between the rework solder station cabinet and a grounded electrical socket. I did this in my basement bathroom as it has an AC outlet that is most easily accessed. Note to self, install a GFE outlet in basement bathroom in the future. The multimeter measured 2.5 Volts AC between rework solder station cabinet and the electrical socket ground. This is within safe levels.
The next test was measuring AC Volts between the metal tip of the hot air gun in holder and the electrical socket ground. The measured voltage was 0 Volts AC, very good!
The next test was measuring AC Volts between the metal tip of the hot air gun out of holder and the electrical socket ground. The measured voltage as 1.8 Volts AC, this is acceptable.
I measured AC Volts between the metal tip of the soldering iron and the electrical socket ground. The measured voltage was 38.1 Volts AC, this seemed a little high and it concerned me.
Until I performed the same electrical testing on another temperature controlled soldering iron and found it to be close to 30 Volts AC as well.
Zeny F2C 2in1 862d+ SMD Rework Soldering Station's soldering iron worked great on soldering a surface mount integrated circuit on the printed circuit board of radio kit I purchased from e-bay.
In addition, I was able to replace this surface mount 8 pin EEPROM in my Magnavox LCD Television using this rework soldering station. Using smallest tip I was able to direct the heat of the hot air gun on the pins of the surface mount integrated circuit then lifted it off the board with tweezers. I was able to dial in the soldering iron temperature where it had just enough heat to solder the surface mount integrated circuit back onto the printed circuit board without damaging the component or the board.
The Zeny F2C 2in1 862d+ SMD Rework Soldering Station would be a great asset to any hobbyists' workbench who has the occasional need to do rework of surface mount printed circuit boards. The integrated soldering iron with multiple tips can replace your current workbench soldering iron.
Youtube Video 862D+ Celcius to Fahrenheit conversion
One of my hobbies is building radios from scratch. I construct them in bread board style fashion. So far my "home brew" radios have all been of regenerative type that require few custom made coils that have 50 turns or less.
My next project is a Super Heterodyne receiver with custom built 400 KHz IF (Intermediate Frequency) transformers. Each IF transformer will require two 620 turn helical coils wound on a cardboard form. This project will require two IF transformer plus a LO (Local Oscillator) coil for a total of five helical coils. As you can see, a Helical Coil Winder Jig will come in handy for this project.
Below is a picture of the finished Helical Coil Winder Jig in action:
Step1: Main Body Construction
I started with a miniature crate I purchased from a local craft store. Woodworking is not one of my strong skills so I always try to start with a finished wood product then modify it for my needs.
I then cut the crate down to size using a jigsaw. The smaller piece to the right in the picture below will be used as the body of my Helical Coil Winder Jig. The rest of the crate will be broken down into its discrete pieces and used in this project.
The end piece from the unused part of the crate was nailed in place to form a small box 4 1/2 x 5 x 6 Inch in size. The nail holes were filled in with wood putty. The wood putty will be sanded down in a later step.
3/8 Inch holes were drilled for the main shaft using a drill press. The holes were drilled approximately 7/8 Inch from the top and centered horizontally.
The surface of the crate was rough. I used an orbital sander with fine grit sandpaper to smooth all surfaces and to remove excess wood putty.
Step2: Main Axle Construction
The main axle is made from a 3/8 Diameter 24 Inch Aluminum Rod. I drilled/tapped a hole on one end. A 10-32 x 4 Inch long screw will serve as the crank handle.
The 10-32 x 4 Inch screw is threaded into the aluminum rod until the head is almost flush with the rod. I then secure it in place with a lock washer and 10-32 nut.
I use a vise to bend the screw 90 degrees in order to form the crank handle. The bend starts about 1 1/4 Inch away from the 10-32 nut.
A 7/8 Inch Diameter dowel is cut down to 1 1/2 Inch and a hole is drilled down the center. This will serve as the crank handle. The hole down the center has to be just big enough to allow the dowel to move freely on the screw without binding.
Step3: Coil Arms Added
Two 10 inch x 1 1/2 arms were made from scrap pieces of the miniature crate then nailed to the base of the main body, flush with the bottom. These arms will hold the copper wire spool.
Here is a picture with both arms nailed in place.
Once again, wood putty was used to cover the countersunk nail heads.
Step4: Counter Added
My Helical Coil Winder Jig will incorporate an electronic counter, in order to keep track of the number of turns of wire, on the coil form. I created a small 2 Inch x 1 1/2 Inch arm to hold the counter. It is nailed to the side of the main body with it pointing up at a 35 Degree angle. Again, wood putty was applied to hide the countersunk nail holes.
The base of the electronic counter was temporarily mounted for fitment. Two small brass screws will hold it in place.
Here is what the electronic counter will look like when it is finally mounted. The counter runs on a watch battery and does not require external power.
The green and yellow wires coming out of the back of the electronic counter are soldered to the printed circuit board inside. Each wire is soldered to a point on the printed circuit board so that I can emulate the count button being press externally.
The green and yellow wires are soldered to a reed switch that will be triggered by a magnet.
The fragile reed switch is encased in heat shrink tubing for protection.
The magnet will be attached to the axle with the reed switch nearby so that the count on the electronic counter is incremented with each turn.
Step5: Coil Holder Construction
I needed a way to hold a variety of different size tubes on the axle during the coil winding process. I established that a cone shape would work best to hold the tubes centered on the axle. Once again a trip to our local crafts store yielded these small bird houses with 3 Inch diameter conical roofs.
A few swift hits of hammer removed the bottom part of the bird houses, leaving only the conical roofs. The rope hanging loops on top were cut off.
3/8 Inch diameter holes were drilled through the centers so that they could be threaded on the axle.
I reinforced the base of each cones with a generous amount of wood glue.
Step6: Protect the Wood
The main body of the Helical Coil Winder Jig was treated to two coats of Minwax Water-Based Semi-Gloss Polyurethane. I use semi-gloss because it is better at hiding imperfections than gloss. Water-based Polyurethane is much easier to cleanup and does not smell as bad as oil-based. Once dry, I lightly sand the pieces with fine grit sandpaper in between coats.
The conical coil holders are also treated to two coats of Polyurethane.
Even the hand crafted wooden knob received two coats of Polyurethane!
Once dry, all the holes in the main body where reamed out with a drill to remove residual Polyurethane that dripped in them during the coating process.
Step7: Final Assembly
A circular magnet was attached with Super Glue to one of the Drill Stop Collars. The magnet was attached opposite of the set screw.
I expanded the center hole in three 1 1/4 inch fender washers to 3/8 diameter so that I could slide them on the axle.
The Drill Stop Collar with the magnet attached was first threaded on the axle and cinched down about an inch from the crank handle. Next, a fender washer was threaded onto the axle. The axle was then threaded through the first hole in the main body.
Then another fender washer was threaded on the axle followed by a spring, fender washer, and another Drill Stop Collar. Finally, the axle was threaded through the other hole in the main body.
The the spring was compressed, then the second Drill Stop Collar to be threaded on the axle was cinched down. This assembly will keep tension on the axle and prevent it from moving backwards when you remove your hand from the crank.
The electronic counter was then attached to the main body. I used hot glue to keep the reed switch in close proximity to the circular magnet attached to the Drill Stop Collar. In addition, the hot glue was used to secure the wiring to the side of the main body.
Time to test the electronic counter, first I press the small silver button to set the counter to zero. Then I rotated the crank four times to made sure the counter reflected the correct number of turns.
Two more 1 1/4 fender had their center holes expanded to 3/8 diameter so that they would slide on the axle. I then mounted them to the base of each conical coil holder with two wood screws.
Automotive hose clamps will hold the conical coil holders in place on the axle.
A second 3/8 Diameter 24 Inch Aluminum Rod is threaded through the two coil arms. This rod will be stationary and hold the copper wire spool. The rod is held in place by two decorative hinges I had left over from another project. Two brass screws hold the hinge to the coil arm. I drilled a hole through the other part of the hinge then through the aluminum rod. A 1 Inch 4-40 screw holds the rod securely to the hinge.
The rod was also secured to the other coil arm in the same fashion.
Step8: Coil Winder in Action!
The conical coil holders can be used in various ways to hold a coil form. Below is the coil form configuration I use when only one side of the coil form is open. I did have to drill a 3/8 hole in the center of closed end in order to thread it onto the axle.
I use the conical coil holders in the following fashion when the coil form is open on both ends.
Typically, I drill two small holes then thread the copper wire through the holes at the starting end.
Before I start winding the coil, I click on the small silver reset button to zero the counter.
When winding the coil, I pinch the copper wire between my thumb and index finger to keep tension on it. You may want to wear gloves as this could cause a blister to form on your finger and thumb tips.
As you start winding the coil you may notice small gaps in the windings. While keeping tension on the copper wire, use your other hand to push the windings together to remove the gaps.
When I get to the proper amount of turns, I place a piece of masking tape on the end to secure the copper wire. Failure to do so will cause your coil to loose tension and unwind. I then use a bead of E6000 clear adhesive to keep the copper wire in place. I typically run beads of E6000 clear adhesive at 0, 90, 180, and 270 degree positions of the tube.
Finally, I use my Mega328 Component Tester to check the Inductance of my newly wound coil. The Inductance should be close to coils with the same number of windings on the same diameter coil form.
You should consider building my Home Brew Helical Coil Winder Jig if you find the need for creating numerous homemade coils for your electronic hobby projects.
A friend of the family gave me this GE T1284A AM/FM tabletop radio. She knew that I restored old radios and thought I would like this one.
The T1284A is unremarkable and is of very common design for a radio from the mid to late 1960s. It is of superheterodyne (superhet) design with an AM IF (Intermediate Frequency) of 455kHz and an FM IF frequency of 10.7 MHz.
It is powered from 117 Volts 60Hz line current, common in the United States, and uses a transformerless design that incorporates a wire-wound resistor to step down the voltage and and a single diode to rectify the current required to power the transistor circuits.
The T1284A incorporates eight transistors, one being of the power transistor type housed in a metal case, that drives the speaker. The audio stage uses a 4 ohm PM (Permanent Magnet) speaker driven by an audio impedance matching transformer.
As unremarkable as this radio was, it did have a handsome wood cabinet and a pretty facade, which motivated me to take this radio on as a remodel project.
Step 1 Disassembly
The first step of any remodel project is to tear down the radio to see what you have to work with. The back cover is the disassembly starting point for the T1284A, one screw, circled in red in the picture below, holds it in place. The back cover fits in a slot, simply pull the back panel down and then straight up to remove.
Below is a picture of the inside of the T1284A.
The Volume, Tone, and Tuning knobs need to removed from the T1284A. They just pull off.
In addition, the AM/FM and AFC switch covers need to be removed.
Two screws, accessible from the back, hold the chassis in place inside the wooden cabinet and need to be removed. There is one in the upper right-hand corner of the cabinet.
The other is located in the upper left-hand corner of the cabinet.
Once the chassis screws are removed, you can tilt the front panel with attached chassis down.
The audio transformer is attached to the bottom of the cabinet. You must first unwind the wire leads from around the transformer in order to gain access to the screws holding it to the cabinet.
Remove the two screws that hold the audio transformer to the base of the cabinet.
You should now be able to pull the back panel through the front of the wooden cabinet. The chassis/front panel and back panel should now be free of the cabinet.
Step 2 Electrolytic Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 50 year old electrolytic capacitors like the ones in the T1284A!
Electrolytic capacitors should be replaced with one of similar capacitance and equal or above Voltage rating. These type of capacitors are also polarized so make sure you observe the polarity of the capacitor to be replaced and install new the same way.
I check each replacement capacitor with my trusty GM328 Multi-Function Tester before installation.
The electrolytic capacitors, circled below, were replaced.
One electrolytic capacitor, that was close to the front panel, had to be soldered to the bottom of the printed circuit board. I was able to get the original out but was unable to thread the replacement through the holes in the printed circuit board from the component side.
Here is a picture of all of the electrolytic capacitors that were replaced.
Step 3 Cleaning and Lubrication
The Volume control caused static to be heard from the speaker while be rotated during initial testing. As such, I decided to spray contact cleaner inside both the Volume and Tone potentiometers then rotate them back and forth several times to clean up the contacts and the resistive element the contacts touch.
Both the exterior and interior of the wooden cabinet were treated with lemon-oil base furniture polish.
Mr Clean MagicEraser sponges work miracles on cleaning vintage electrical cords! I apply an Armor All like protectant to the cord after it has been cleaned and dried.
Volume, Tone, and Tuning knobs are cleaned with a toothbrush and water then throughly dried.
No amount of metal polish is going to clean up the AM/FM and AFC switch covers. Their chrome finish is pocked and badly corroded. They will have to be painted.
I used Windex to clean the front panel including the speaker grill. Windex is my go-to universal cleaner.
Q-tips moistened with Windex work great for cleaning crevasses and hard to reach corners.
Look how dirty the paper towel was, just from cleaning the front panel.
I took this opportunity to lubricate the shaft of the Volume and Tone controls as their rotation was very stiff. I use Labelle 107 Oil as it is safe on plastics and I have it around for my model train hobby.
I also lubricated the shaft of the Tuning control.
In addition, I lubricated the Tuning control shaft on the back side of the front panel that connects to the variable capacitor and Tuning dial via a dial cord.
Step 4 Prep and Paint
I am going to paint several things on my T1284A:
The AM/FM, AFC switch covers were wet sanded with a 800 grit sandpaper to smooth out the surface and remove the pock marks due to corrosion.
I mounted the AM/FM, AFC switch covers to the end of Q-tips then degreased their surface with Prep-All. They are now ready for paint.
Two coats of silver paint and the switch covers look like new!
The first step on painting the outer border of the front panel is to mask off everywhere you don't want painted. I use a product called Frog Tape and brown paper to mask off the areas to be painted. Frog Tape has something called PaintBlock which makes crisp lines between painted and unpainted areas. I then degrease the surface to be painted using Prep-All.
Two coats of silver paint were applied to the area of the outer border.
Here is the finished product, once the Frog Tape and brown paper have been removed.
A lot of vintage radios I restore had painted accents on the knobs that have worn off due to normal wear/tear. I have tried to hand paint the accents but my hand is not steady enough and they look "amateurish".
I came up with a new way to paint the accents using a Sharpie Paint Pen and a drill. I mount the base of the knob in the drill and then apply the paint pen while the knob is spinning.
The results look very professional!
Step 5 Assembly
Time to mount the chassis/front panel back into the wooden cabinet. You will need to thread the back panel through the front of the cabinet first.
Time to install the two screws that hold the chassis/front panel to the cabinet. There is one screw on the left-hand side.
Another screw needs to be installed on the right-hand side.
The audio transformer was reattached to base of the cabinet with two screws.
I wrote the model number with permanent marker on the back of the heat sink attached to the chassis.The original sticker on the back panel that held this information had been bleached out by the sun and was unreadable.
During assembly, I noticed that the nut that holds the earphone jack on the back panel was rusted.
I treated the nut to a coat to silver acrylic enamel paint I had on hand for my model railroad hobby.
Time to reattach the back panel. A single screw on the bottom holds it in place.
The AM/FM and AFC switch covers were reinstalled.
I noticed some grime around the holes where the Volume, Tone, and Tuning controls protrude from the front panel. I used a Windex moistened Q-tip to clean.
Finally, I installed the Volume, Tone, and Tuning knobs. Here is the final result.
My General Electric T1284A AM/FM Radio in Action!
In a previous blog on radioboatanchor.com, I restored a Hallicrafters S-72 portable receiver. Here is a before and after picture of my S-72.
Click on the button below to visit my blog about rebuilding my Hallicrafters S-72.
What made the S-72 "portable", besides the carry handle, is that it could be operated under battery power. I am not talking about a 9 Volt or two AA batteries, this radio had a compliment of eight miniature tubes which required a 90Volt "B" battery for the tube's anodes and a 7.5Volt "A" battery for their filaments. A battery pack was designed to combine the A and B batteries into one convenient package. In the picture below, the empty area behind the chassis is where the battery pack was installed, a black cloth strap held it in place.
Below is a list of compatible battery packs for the S-72, straight out of the manual. Your local hardware or DIY store will not have them as these battery packs have not been produced since the 1960s!
Below is a picture of the completed S-72 battery box, which will replace the original battery pack. I will be wiring 9 Volt batteries in series to simulate the 90 Volt DC "B" battery. In addition, I will be wiring several D batteries in series to simulate the 7.5 Volt DC "A" battery.
Battery Box Contruction
I started out with this 15 Inch mini wood crate I purchased from a local crafts store.
Mini wooden crates on Amazon!
I partially disassembled the mini wood crate. With some carefully placed cuts I was able to reduce the crate's overall dimensions to 2.75 in x 11in x 5.25in. This was approximately the size of the original S-72 battery pack. I used finishing nails and wood glue to hold the new structure together.
Time for a quick check to ensure the new battery box fits into the S-72. Looks like it is a perfect fit!
I was able to reuse a scrap wood piece I cut off the original mini wood crate to fabricate a hinged top piece. This hinge piece is required to ensure the structural integrity of the battery box as it is being strapped down to hold it in place inside the cabinet. It is hinged so that you can easily access the batteries inside. The tiny brass hinges, screws, and hasp were all acquired at a local crafts store.
The S-72 chassis connected to the original battery pack using a single connection. I found that a standard octal tube socket mates perfectly with the S-72's connection. Here I used two pieces of scrap wood from the crate to fabricate a mount for the octal tube socket. The wood pieces are held in place with finishing nails and wood glue.
Tube sockets on Amazon!
A leftover hinge and brass screw reinforce the octal tube mount from the inside of the battery box.
I will be connecting ten 9 Volt batteries in series for the 90 Volts DC "B" battery. The batteries will be aligned facing up for easy access to their terminals.
I am using a wooden paint stirrer, cut to the proper length, to hold the 9 Volt batteries in place. At each end, I bent a solder lug in order to form a make-shift right-angle bracket. The right-angle bracket can be adjusted slightly then tightened down to form a tight fit against the 9 Volt battery cases.
We only need five "D" 1.5 Volt batteries wired in series to achieve the required 7.5 Volts for the "A" battery. I have mounted three twin D battery holders, one battery slot will not be used. I also added a 9 Volt battery holder, circled in red. This will hold an extra 9 Volt battery connected in series to boost the B battery voltage back up to 90 Volts DC as the 9 Volt batteries start to drain.
The nail-gun countersunk the finishing nails I used to assemble the battery box. I used wood putty to conceal their holes.
I used an orbital sander with fine (150 grit) sandpaper to sand the wood putty flush with the wood and to smooth out the rough cut wood used in the original mini wood crate.
I also used the wood sander to sand smooth the hinged tops and to remove the labeling on the wooden paint stirrer used to hold the 9 Volts batteries in place.
Here is a picture of the battery box parts after sanding.
I then treated all wooden battery box parts to two coats of water based polyurethane, followed by light sanding and then a final coat.
As mentioned, the 1.5 Volt D cells must be connected in series in order to achieve the required 7.5 Volts DC for the "A" or filament power supply. I wire the D cell battery holders in series except for the one slot, circled in the picture below, that will not be used.
The eleven 9 Volt battery clips are connected in series. While ten fully charged 9 Volt batteries in series will achieve 90 Volts DC, I included an extra battery clip to introduce another battery in the circuit to boost the voltage back to around 90 Volts as the 9 Volts battery's voltage drops as they discharge. This eleventh battery clip is jumpered when fresh batteries are used.
I used a gold paint pen to label each 9 Volt battery clip.
I attached rubber feet to the side of the wooden paint stirrer that comes in contact with the 9 Volt batteries.
This will prevent the batteries from shifting sideways in their mount.
Time to wire the octal tube socket I am using as a female connector. I plugged the male connector from the S-72 chassis into the tube socket in order to determine the proper connections for 90 Volts DC, 7.5 Volts DC and Ground. For reference, here is how the the male connector from the S-72 chassis is wired.
Time to mount the octal tube socket used as a connector to the battery box.
Here is a picture of the battery box with 9 Volt and 1.5 Volt D cells installed. Eleven 9 Volt batteries are installed as they are older batteries and their Voltage is dropping under load. Five D cells are installed with one battery slot left open.
Batteries on Amazon!
Time to test before installing the battery box into the S-72. I first test for the "B" battery voltage, which should be around 90 Volts DC.
Then I test for the "A" battery voltage, which should be around 7.5 Volts DC.
Time to do some initial testing, I already had my S-72 chassis out of the case for cleaning. This made it easy to connect the chassis to the battery box. After a brief warmup, the S-72 sprung to life and I could immediately hear a local sports talk station in the standard AM broadcast band.
Note, the plug on the line cord must be plugged into the chassis, in order to run on battery power. See area circled in the picture below.
After the S-72 chassis was once again safely installed in the cabinet, it was time to install the battery box. Once the battery box is in place, you secure it with the black cloth strap built into the cabinet. You must also connect the chassis to the battery box. The connection point is circled in the picture below:
A final test is to see if the S-72 cabinet side door closes properly with the custom battery box installed. Looks like it is a perfect fit as the side door closed and latched properly.
Finally, here is a picture of the finished product!
Here is a video of my battery powered S-72 in action!
Below are before and after pictures of the chassis of my Hallicrafters S-72 Portable Receiver. I think you'll agree that my rebuild was a complete success!
About the Hallicrafters S-72
The S-72 is a Superheterodyne radio receiver built by Hallicrafters and sold from 1949 to 1953. This model covered the standard AM broadcast band. In addition, it covered three shortwave bands with continuous coverage from 540Khz all the way up to 30Mhz.
An internal loop antenna was used for standard AM broadcast band reception while a telescopic whip antenna is used for shortwave reception.
This radio employs eight miniature tubes and one Selium rectifier.
Here is the miniature tube compliment:
1T4, 1U4, 1R5, 1U4, 1U4, 1U5, 1U5, 3V4
The S-72 has an RF Amplifier, Mixer, Two IF (Intermediate Frequency) Amplifiers, Detector, and Audio Output stages. These stages are common in most AM radio receivers. In addition, it has a BFO (Beat Frequency Oscillator) for CW (Continuous Wave) or Code reception. Band change is accomplished by a four position selector switch that connects in different LC resonant tank circuits in the RF Stage.
Controls of the S-72 are fairly common, it has a Tuning, Band Spread, Band Selector, and On-Off Volume controls. The Voice-Code controls wether the BFO is on for Code reception and the frequency of the oscillator. There is also a "phones" jack for listening in noisy areas.
Powered could be derived from a dry cell battery pack. You have to insert the line cord plug into a receptacle located on the chassis to run on battery power.
The S-72 could also be powered from 105 to 125 Volts AC or DC line power as apparently direct current was still used in some areas.
The S-72 electronics were housed in a portable luggage style cabinet with a carry handle on top. I am not sure if "portable" is the proper term given that it weighs a whopping 16 pounds without the battery pack!
Access to the controls and dial is achieved by opening of the top cover. Access to the battery, line cord, and electronics is done through a side cover.
The S-72 retailed for $109.95 the first year of sale (1949).
The inside of my S-72 was in pretty good shape, although very dusty. All the vacuum tubes were in place and the two air capacitors, one for tuning the other for band spread, looked like they didn't have any bent plates. The empty area in the bottom is where the battery pack is housed. The black strap in cinched down and keeps the battery pack from moving around during transport. A single plug connects the battery pack to the chassis.
As you can see from the picture below, the faceplate, knobs, and whip antenna are missing from my S-72. The chassis was hastily put in place inside of the case and the two nuts that hold it in place were missing.
The external phone jack was just floating freely inside the case. See area circled in the picture below.
The manual, including schematic and alignment instructions, for the S-72 can be obtained from radiomuseum.org at no cost. Click on the button below to go to the web page.
"Old Time Radios! Restoration and Repair" book on Amazon
I consult this book often during radio restoration. I grew up in the transistor and diode era and this book taught me a lot about vacuum tube and selium rectifier technology.
Step 1 Chassis Removal
As mentioned, just two bolts hold the chassis in place. The nuts that secured the chassis to the inside of the cabinet were missing from my S-72.
Here is a picture of the bottom of the chassis. The discrete parts (resistors, capacitors, transformer, coils) are dirty but in fairly good condition. Notice the blackened area in the lower left area of the chassis. It looks like there might have been one or more component failures in this area. I will need to investigate the components carefully in the blackened area before ever applying power.
Step 2 Chassis Cleaning and Lubrication
Contact cleaner was applied to all of the Band selector's contacts. I then moved the selector to all four positions in order to clean the contacts.
I applied Labelle 107 Oil to the shafts of all dial indicator pulleys. I have this oil on hand due to my model train hobby. This oil will will not harm plastic components.
In addition, I applied this oil to the shafts of the Tuning, Band Spread, Band Selector, On-Off Volume controls and Voice-Code controls.
Labelle 107 Oil was also applied to the shafts of the Tuning and Band Spread Variable Capacitors.
Labelle 106 Grease was applied to the bearing located to the front of the Tuning and Band Spread Variable Capacitors.
Labelle lubricants on Amazon
I use Labelle oil and grease for my radio restoration projects. I already have these products around as I am also a model railroad enthusiast. These products will not harm plastic.
The exterior of the chassis was cleaned with paper towels moistened with Windex glass cleaner. I use Q-Tips moistened with Windex to get into hard to reach places.
Step 3 Check Vacuum Tubes
Unlike semiconductor transistors that have a near infinite lifespan, vacuum tubes age and become less efficient. In addition, their filaments burn out rendering them inoperable. It is always a good idea to test all vacuum tubes in a radio you are servicing before doing any more troubleshooting.
In addition, make sure that that the right tube is in the right socket. This will save you troubleshooting time later.
Pictured below is my Eico Model 635 Vacuum Tube Tester testing a tube from the S-72.
Step 4 Electrolytic Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 65 year old electrolytic capacitors like the ones in the S-72!
Step 4a - Restoring the Multi-Section Capacitor
Multi-section capacitors, which were aluminum cans containing several discrete capacitors all connected to a common ground, were popular in the 1950s. There were used mostly in the power supply sections of vintage electronic devices. You can purchase replacement multi-section capacitors but they are expensive. I typically rebuild them by replacing their guts with inexpensive discrete capacitors of the same or slightly greater capacitance and working voltage. The multi-section capacitor in the S-72 is circled in the picture.
The multi-section capacitor in the S-72 contains the following discrete capacitors:
Capacitor A 60uF @ 150Volts
Capacitor B 20uF @ 150Volts
Capacitor C 20uF @ 150Volts
Capacitor D 2000uF @ 15Volts
The components connected to it's base terminals, circled below, must be desoldered before removing it from the chassis. I labeled each connection during the desoldering process.
The phenolic base is held in place with two rivets, they must be drilled out. Later, they will be replaced with machine screws, lock washers, and nuts.
Here is a picture of the multi-section capacitor removed from the chassis. The four solder lugs in the center connect to the positive side of the internal electrolytic capacitors. All internal capacitors share a forth common solder lugs at the rim for their negative connection.
I use wire cutters to uncrimped the bottom of the multi-section capacitor. Then I use needle nose pliers to pull the crimped sections away from the base. This allows me to pull the guts of the multi-section capacitor out of the aluminum can.
The anatomy of a multi-section capacitor. The four internal electrolytic capacitors are rolled up into one assembly.
I was able to fit all four replacement electrolytic capacitors inside the aluminum can. A dab of hot glue holds the components in place. I use tiny brass screws I get from a local craft store as solder anchor points.
Pictured below is the refurbished multi-section capacitor installed back into the chassis.
All of the components attached to the multi-section capacitor have been soldered to its bottom terminals.
I use a Dremel with cutoff tool to remove the area from the base of the multi-section capacitor's aluminum can that I bent with needle-nose pliers.
I then use the Dremel with wire brush tool to remove burrs.
I spray the external cardboard wrapper of the multi-section capacitor's aluminum can with some flat black paint to make it look as good as new.
Hot glue holds the aluminum cover in place over the multi-section capacitor's base. You will never know it was refurbished once the aluminum cover is installed!
There is one other 100uF capacitor capacitor, circled below, that also needs to be replaced.
The top electrolytic capacitor in the picture below is the original 100uF 25Volt capacitor, the bottom one is its modern equivalent. Notice how the new modern equivalent is in a much smaller package?
Circled below is the newly installed 100uF 25Volt capacitor.
Step 5 Replacing Paper Capacitors
Paper capacitors, like the ones circled below, become very unreliable with age and should be replaced with one of similar capacitance and equal or above voltage rating. Paper capacitors are not polarized although they may have a black band on one side indicating which lead is connected to the outside foil.
I replace paper capacitors with new Polypropylene type. Circled in the picture below.
I almost forget to replace the paper capacitor that is on the top side of the chassis. This capacitor is part of the antenna circuit.
Here is a pic of the new Polypropylene capacitor soldered in place.
Step 6 Selenium Rectifier Replacement
The S-72 employs a Selenium rectifier, circled below, to convert household AC (Alternating current) current to DC (Direct current) required by the receiver. As Selenium rectifiers age, their forward resistance increases to the point where it causes the power supply voltage to drop. Initial testing while powered by household current showed that the B Voltage, measured at capacitor C38c, was below the specified 90 Volts DC.
Below is a comparison in size of a Selenium rectifier compared to its modern replacement, a 1N4005 Silicon rectifier. The 1N4005 has a forward current rating of up to 1 Amp where the original Selenium rectifier only have a forward current rating up to 150 Milliamps.
When replacing the Selenium rectifier with a modern 1N4005 Silicon rectifier, I had to install a 100 Ohm tapped wire-wound resistor in series with it as a Silicon rectifier is much more efficient. I then adjusted the tap on the wire-wound resistor until I measured the desired "B" Voltage of 90 Volts DC at capacitor terminal C38c.
I was having issues with filament or "A" Voltage being below the specified 7.5 Volts DC. This voltage is measured at capacitor terminal C38a. With the power off, I performed some resistance checks and determined that part of the tapped wire-wound resistor, R29 in the schematic, had increased in resistance and was out of spec. I connected a 75 Ohm 25 Watt wire-wound resistor in parallel to decrease its equivalent resistance. The filament Voltage once again rose to the required 7.5 Volts DC.
Step 7 Marking the Hot side of the AC plug
Depending on how the non-polarized line cord plug of the S-72 is plugged into a power outlet, an high voltage potential can exist on the metal chassis. Below my Multimeter is reading 120 Volts AC between the chassis and ground, in this case ground is the metal enclosure of the household sockets. This poses a potential shock hazard!
Now, if I reverse the line cord plug, I get a very low voltage (less than one Volt) AC between the chassis and ground.
Normally, I would install a polarized plug on the end of the radio's line cord, ensuring that the chassis was at or near ground potential. I can't do that with the S-72 as you have to plug the line cord plug into the slots on the top of the chassis in order to operate on battery power.
Since I could not install a polarized plug, I marked an "H" for Hot on the side of the plug that should go into the smaller slot on the AC socket. If properly wired, the smaller slot on the household AC socket is "Hot" or 120 Volts AC with reference to ground. The larger slot on the household AC socket is "Neutral" and it should be less than 1 Volt AC with reference to ground.
Step 8 Alignment
btuIf is a perfect time to perform the alignment procedure, as the S-72 chassis is already removed from the cabinet. Alignment involves injecting a AM modulated signal, of frequency specified in the manual, then watching for maximum AC Voltage measured at the speaker terminals. This is done while tweaking variable capacitors if the input frequency is at the high end of the band or ferrite slugs in RF coils if on the low side of the band. You must perform this process for each position on the Band switch. Page 6 of the S-72 manual explains the process. There is button called "Hallicrafters S-72 Manual" in the beginning of my blog that will take you to a web page where you can obtain the manual.
Step 9 Cabinet Cleaning and Restoration
The S-72's cabinet is covered in a leatherette material with brass accents. I sprayed the exterior with Windex then wiped it down with a paper towel. I repeated this process, discarding the paper towel and getting a new one, with each cleaning cycle. The process was repeated until the paper towel showed very little evidence of dirt. Below is a picture of my paper towel on my first cleaning pass.
Meguiar's Motorcycle All Metal Polish was used to remove years of oxidation from S-72's brass plated feet.
Meguiar's Motorcycle All Metal Polish was also used to shine up the brass plated air vents in the side access door and the pull handle.
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Meguiar's Metal Polish works great on the brass and chrome fixtures on vintage radios.
The air vents and pull handle on the side access door cleaned up pretty good. Unfortunately, this was not the case for the brass plated hinges, they were badly rusted with most of the brass plating gone.
I decided it was best to paint the hinges on the side access door. First, I applied masking tape around the hinges to ensure that I would not mar the leatherette exterior. I then used my Dremel with wire brush attachment to remove as much rust and corrosion as possible in order to prep for paint.
I wiped down the hinges with Prep-All, a degreaser and de-waxer used for automotive paint prep. I then masked off the side access door, so that only the hinges were exposed. The hinges were treated with a coat of brass colored Acrylic Enamel spray paint.
The hinges turned out really great! The brass colored Acrylic Enamel spray paint adhered really well to the old hinges.
I also wire brushed the heads of the screws that attach the side access door to the cabinet, degreased with Prep-All, then treated them to a coat of brass colored Acrylic Enamel spray paint.
The leatherette material that covers the cabinet was coming off in places. I used Elmer's School Glue to adhere it back to the cabinet.
I cleaned the inside of the cabinet with a lemon-oil based furniture polish.
I sprayed then wiped down the outside of the cabinet with an "Armor All" like protectant that I purchased from a local auto parts store.
The lid was also sprayed and wiped down with an "Armor All" like protectant.
Step 10 Front Panel Replacement
The front panel was missing from my S-72, I believe a previous owner was using this as a "parts" radio.
Luckily, I have a father-in-law with a CNC router setup in his garage. He was more than happy to fabricate a new front panel for me. First, I needed to plot out the dimensions for the panel to give him. I put my drafting skills to work.
Next, I created a paper template from my dimensions to double-check for fit.
I then scanned to PDF my front panel drawing with dimensions then e-mailed it to my father-in-law who lives on the California. A few weeks later I received the finish faceplate in the mail. It was beautiful! My father-in-law machined it out of a composite material that consist of a layer of plastic sandwiched between to sheets of thin aluminum. I checked the new faceplate for fit, by temporarily installing the chassis into the cabinet and installing the knobs.
The new front panel fit perfectly. I decided it was a good idea to install the dial lens and to glue the new speaker grill cloth in place before installing the front panel.
The front panel is going to be glued to the top of the S-72 cabinet. I am going to use large fender washers secured with screws and bolts to hold the face plate in position while the glue dries. I put electrical tape on the side of the fender washer that is to comes in contact with the front panel so that is does not mar the surface.
I put a bead of E6000 adhesive on the back of the front panel.
Once the front panel was aligned properly on the cabinet, I used the fender washers with nuts and bolts to secure it in place while the adhesive dries. I used the phone jack to secure the upper right-hand corner.
Here's how the front panel looks once the fender washers, nuts, and bolts have been removed. Notice that the holes in the front panel are slightly out of alignment with cabinet holes. The knobs will conceal this alignment problem.
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Step 11 Assembly
The original antenna mounting bracket was missing from my S-72. I fabricated a new one from an aluminum heat sink I had in my junk drawer. This heat sink already had a solder lug attached to it which made it easy work to solder it to the external antenna connection on the chassis.
In order to make handling the chassis easier, I removed the phone jack. Now, I had to connect it back in before the chassis was inserted into the cabinet.
The chassis slips in through the side panel and is held in place by two bolts built into the inside of the cabinet. I had to supply my own lock washers and nuts as the originals were missing.
I found a suitable replacement telescopic whip antenna on Amazon. My fabricated antenna bracket is held on the side of the cabinet with tiny brass screws I purchased from a local crafts store.
When mounting the knobs, I place a slim piece of cardboard underneath them while tightening the set screw so that each knob is a uniform distance from the front panel.
Time to attach the side panel. It is held in place with four screws. These screws are the ones I painted earlier in my blog.
With the side panel in place you must solder the two connections between the chassis and the built-in loop antenna (circled below).
I built a battery box that contains 9 Volt batteries connected in series to supply the required 90 Volts DC and 1.5 Volt D Cell batteries connected in series to provide the required 7.5 Volts DC. A tube socket is mounted to the side of the battery box. The battery connection from the chassis plugs into the tube socket. I have a separate blog that covers the battery box construction.
You must plug the line cord into the chassis in order to operate from battery power.
Hallicrafters provided these handy leather straps in order to tame the line cord.
Here is a picture of my S-71 with custom battery box installed.
A final test is to see if the side door closes properly with the custom battery box installed. Looks like it is a perfect fit as the side door closed and latched propertly.
Finally, here is a picture of the finished product!
Video of my newly rebuilt Hallicrafters S-72 in action!
I have a high-stress job in the Information Technology field. At lunch I trade my dress shoes for walking shoes and walk my employer's campus, and several other industrial parks in the area. I use walking as a way to reduce stress, clear my mind, and prepare for tasks that need to be completed by the end of the working day.
Recently I noticed a dumpster at one of the industrial parks, and maintenance workers cleaning out a properly, readying it for the next lessee. The dumpster was only shoulder height, the style used to haul away construction waste. I glanced in the top of the dumpster as I strolled by and noticed a compete stereo system strewn of top of old lumber. The stereo system consisted of the following components:
Fisher CA-273 Stereo Amplifier
Fisher EQ-273 Graphic Stereo Equalizer
Fisher FM-273 AM/FM Stereo Synthesizer Tuner
Fisher AD-813 CD Player
I could tell that the components of this stereo system had not seen the light of day in many years. I made several walking strips between the dumpster and my car until all the components of my "dumpster" stereo were safely deposited in the trunk.
Although I have recovered the above stereo components, this blog is going to cover the repair of the CA-273 Stereo Amplifier only.
About the Fisher CA-273 Stereo Amplifier
The Fisher CA-273 Stereo Amplifier was first introduced in 1983. It was intended to be used with FM-273 Tuner, CR-273 Cassette Deck, EQ-273 Graphic Equalizer, and MT-273 Turntable. The CA-273 Stereo Amplifier had impressive specs for the time. It could provide 100 Watts RMS power to the speaker with .09% Total Harmonic Distortion. Its audio bandwidth was between 20Hz to 20kHz. On the back it included Phono, Tuner, CD, Aux and Tape inputs. In addition, the CA-273 has two switched and one unswitched outlet so the you could provide power to other stereo components. The front of the CA-273 included input Function Selector, 3-band Tone Control, Power Level Indicators, Balance, and Volume controls.
Step 1 Initial Cleaning
My dumpster find CA-273 was covered in dust and dirt. In addition, it had been recently rained on.
I sprayed the CA-273's exterior with Windex then cleaned with paper towels. I buy Windex in "Refillable" 1 Gallon jugs as I use so much of it around the house. I then transfer Windex from the refillable jugs to generic spray bottles.
I use Windex moistened Q-Tips to clean hard to reach spots, like between the RCA jacks.
A moistened Magic Eraser sponge works great for cleaning dirty AC cords.
Look at all of the dirt Magic Eraser removed from the AC cord.
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A fine tip permanent marker works great on concealing any scraps or gouges in the top cover's paint.
I used a store brand protectant, an equivalent to Armor All, to bring out a nice sheen to the exterior plastic and metal painted parts of the CA-273.
I then used a lint free cloth to buff the exterior of the enclosure and to remove any lint deposited from the paper towels during cleaning.
Step 2 Initial Testing
Once I cleaned all of the Fisher components found in the dumpster, I connected them together via RCA cables, added speakers and an FM antenna then powered everything up. All components powered up but I noticed I was missing the left audio channel in its entirety. In addition, the CD player would not detect an audio disc, but this is material for another RadioBoatAnchor blog. In order to determine if the issue was with the CA-273 Stereo Amplifier or an external component, I switched the left and right audio cables between the FM-273 Tuner and the CA-273 Stereo Amplifier. There was still no sound from the left audio channel, indicating an issue with the CA-273 Stereo Amplifier.
Step 3 Disassembly
Disassembly was required in order to diagnose the issue with left stereo channel. The first step in the disassembly process is to remove the top metal cover. It is held in place by two screws on both sides. See areas circled in the picture below:
In addition, there is one screw, circled below, that holds the top metal cover down in the back. This screw must also be removed.
You can now access the component side of the main printed circuit board.
Four screws hold the bottom metal cover in place. See areas circled in the picture below:
You can access the foil side of the main printed circuit board, Darlington Power Packs, and the power transistors used to regulate the DC power supply, once the bottom metal cover has been removed.
Step 4 Troubleshooting
Once the top and bottom covers of the CA-273 were removed, I could start my troubleshooting. I was unable to find a free schematic on the Internet for the CA-273 so I was left to my own devices as it seemed silly to spend $25.00 on a Sam's Photofact Service manual when the amplifier was "free".
The first thing I did was check the fuses, circled in the picture below. I do a continuity check of each fuse as I have been fooled by doing visual checks before.
In my case all of the fuses checked good. Next, I swapped the Darlington Power Packs, circled in red below. The Darlington Power Packs are the semiconductor components that directly drive the speakers. I would know if a Darlington Power Pack is defective after the swap as the stereo channel problem would have migrated from the left to right channel.
The Darlington Power Pack swap is relatively easy. Two screws hold each in place. A desolder tool quickly sucks away any molten solder from the pads.
Swapping the Darlington Power Packs did not cause the issue to migrate from the left to the right channel, thereby, I must deduce that a Darlington Power Pack was not the issue. Do NOT try to swap the transistors circled below. They are part of the regulator circuit for the positive and negative DC power supplies are are NOT interchangeable.
I came up with a great idea of using the CA-273 as a Signal Tracer, in order to determine where the fault lies. I set the CA-273 on its side and powered it on. I then connected one terminal of my home brew audio generator to the CA-273 chassis and the other to the a multi-meter test lead.
I set the volume control of the CA-273 to about 75% of its travel. I then placed the tip of the multi-meter test lead, connected to my audio generator, in close proximity to components on the main printed circuit board. I would hear a tone from the audio generator, out of the left or right speaker connected to the CA-273, if their was not an issue with that circuit stage. Do NOT touch the multi-meter lead to an actual lead of a component or you may hear the audio tone at close to 100 Watts RMS!
The main printed circuit board in the CA-273 is roughly divided into three sections. The Left Audio Channel (circled in red), the Right Audio Channel (circled in yellow), and the DC Power Supply (circled in blue).
I had determined that nothing was wrong with the main printed circuit board. Circled below are connections between the main printed circuit board and printed circuit board with the volume control. The connection circled in red is for the left audio channel while the connection circled in yellow is for the right audio. I could hear the audio generator's signal from either channel if I brought the multi-meter lead close to them. The printed circuit board with the volume control feeds audio signals into the main printed circuit board.
When looking at the front of the CA-273, you will see a vertically mounted printed circuit board toward the right-hand side of the chassis. This printed circuit board handles Function selections, switching between different inputs, such as Phono, Tape, Tuner, and CD Player. The connector circled in red below connects this printed circuit board to the printed circuit board with the volume control. When I hovered my multi-meter lead over this connector. I could hear the signal generator's audio tone out of the right speaker but not the left. This indicated that the issue is on the printed circuit board with the volume control.
Knowing that mechanical controls are often a problem, especially with equipment that has been dormant for a long time, I decided to fool with the volume control to see if that was the issue. I adjusted the volume control slider to about a quarter length of its travel. I then connected my audio generator to the left channel Tuner input and played with the volume control slider knob. I found that the left channel would work if I twisted the volume control slider knob slightly. This indicated that the volume control slider carbon track for the left channel was dirty or oxidized and needed to be cleaned.
Step 5 Front Panel Removal
As I already had the CA-273 apart, I decided to disassemble the front panel. This allowed me to better concentrate the contact cleaner in the areas that needed to be cleaned. I was also afraid that the dripping contact cleaner residue could dissolve surrounding plastic parts. I also decided to clean the innards of the Tone and Balance controls as well.
In order to remove the front panel, you must first disconnect the wiring between the audio input printed circuit board and the front panel. In addition, you must disconnect the wiring between the main printed circuit board and the front panel. See areas circled in the picture below.
The bezel attaches to the front panel with three screws on the bottom and at the inner lip at the top. The Function Selector switch is part of the front bezel so I had to pull the wiring through the opening in the front panel in order to free. I also had to remove the silver knobs from the three Tone Control sliders.
Behind the front bezel is a metal panel where the volume control printed circuit board and power level indicator are installed. In order to free the metal panel you must remove several screws. There is a screw on each side, circled in the picture below:
In addition, you must remove several screws on the bottom to free the metal panel. Their locations are circled below.
Screws holding the power switch, and the printed circuit board containing the Speaker and Tone switches, need to be removed. The clip holding the headphone jack needs to be removed as well. In addition, the cream colored plastic pieces on the Speaker and Tone switches must be removed in order to free the printed circuit board from the front panel.
Here is a picture of the CA-273 front panel.
Here is a picture of the CA-273 with the front panel removed.
Step 6 Front Panel Slider Control Cleaning
Through my experience, I have learned that slider potentiometer controls don't age well. Due to their open construction, they are more prone to problems with dust and dirt than enclosed rotary ones. The next step is to free the volume control printed circuit board from the metal panel.
I removed the silver knob on the slider Volume control. The black plastic mount must also be removed, it is held in place with one screw. I also performed these same steps for Balance, the slider control to the immediate left.
I removed ten screws that held the volume printed circuit board to the front panel. You must also remove the Tone control indicators from the slider switches. See areas circled in the picture below:
Finally, time to clean the Volume, Balance, and Tone slider controls. I sprayed a small amount of contact cleaner in each slider's slot then worked them through their complete motion several times.
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Step 7 Testing
It is always a good idea to perform testing before buttoning everything up. I re-attached the volume printed circuit board to the front panel. The front panel was then fastened to the chassis and all wiring between the front panel, main, and audio input printed circuit boards were connected. The Function Selector switch is built into the front bezel. I had to connect the wiring between the front bezel and the audio input printed circuit boards.
I plugged the CA-273 into an outlet then powered it on. I then set the Function selector to Tuner, the Balance slider centered, and the Volume slider to about 1/8 of its travel. I then introduced and audio signal from my audio generator to first the left then right RCA Tuner Input jacks.
SUCCESS! I was able to hear the tone first from the left then the right speaker, the issue had been resolved.
Step 9 Detailing
I like to polish the chrome knobs before assembly. This is the perfect time to do it as the knobs have been removed from their control. Meguiar's Motorcycle All Metal Polish works great for polishing and removing oxidation from chrome coated plastic knobs, like the ones used in the CA-273.
Here is a picture of the CA-273's chrome knobs after being polished.
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Step 10 Assembly
Time to button the CA-273 up. I followed Step 5 Front Panel Removal, in reverse order, to assemble the front panel and attach to the CA-273 chassis. Then following Step 3 Disassembly, in reverse order, to install the top and bottom metal covers.
Step 11 Final Testing
Once the CA-273 was put back together it was time for a final test. Once again, I connected the CA-273 Stereo Amplifier to the FM-273 Tuner, EQ-273 Graphic Equalizer, and AD-318 CD Player via RCA cables. I then added speakers and an FM antenna then finally powered everything up. All components powered up and my left audio channel was once again working!
Bringing the Fisher CA-273 Stereo Amplifier back from the grave was a most satisfying endeavor. It is one less thing destined for a landfill. I have yet to service the AD-318 CD Player, it will be the focus of another RadioBoatAnchor blog. The remaining Fisher components grace my basement workshop and provide background music while I toil away on the next restore project.
My Heathkit XR-1L
I was the winning bidder of the vintage Heathkit XR-1L AM Radio from an online auction site. I didn't have much competition as Heathkit Ham Radio and High Fidelity Stereo equipment are more widely sought after. My XR-1L was basically intact except that the moulded leather handle was missing.
There were scuffs and scratches on the leather case due to normal wear and tear.
There was a lot of rust and corrosion on the radio chassis, probably caused by chemicals inside dead leaking batteries left in the radio by a previous owner. The battery compartment, shown at the bottom of the picture below, was very rusty.
I have a soft spot for Heathkit radios and equipment. As a child I remember my dad being hunched over our dining room table on any given evening, building various pieces of Heathkit equipment. It was my job to inventory all of the discrete parts and to place them neatly in cardboard egg cartons we used as organizers. In addition, I would hand my dad the parts required during the assembly process. At the end of each building session, we would have to carefully move all of the parts to the top of the dresser in my parents bedroom, in order to clear the dining room table for the next meal. The dresser was high enough that it prevented my two young toddler sisters from being able to access it. My parents, two sisters, and I lived in a small three bedroom ranch in a suburb of Cleveland, there was very little extra space for hobbies, other than the dining room table. My dad and I working on Heathkit equipment brings back fond memories, as such, I have become an avid collector of vintage Heathkit equipment.
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Step 1 Initial Testing
In order to establish a baseline of my radio's performance, I decided to power it on to see if it would pick up any stations, prior to restoration. First I removed the chassis from its leather case. Only two screws, circled in red below, hold the chassis in the case. First I had to remove the Tuning and Power/Volume knobs, they just pull off. The chassis pulls straight back and out of the back of the case, once the screws were removed.
As you can see below, the chassis of the Heathkit XR-1L AM Radio is truly a self contained unit. Even the speaker is mounted on standoffs to the component side of the chassis. This radio required 9 Volts, typically supplied by six D Cell batteries. For initial testing purposes, I used a 9 Volt battery, jumpered to the proper connections in the battery compartment to provide power. Initial testing was promising, I immediately heard atmospheric hiss once I turned the volume control to the On position and then set the volume to about midpoint of its range. With some fiddling of the tuning dial, I as able to hear a couple of stations in my regional area that I know have a strong signal. My Heathkit XR-1L was functioning, but its sensitivity left much to be desired.
Step 2 Electrolytic Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 60 year old electrolytic capacitors like the ones in my Heathkit XR-1L!
Electrolytic capacitors should be replaced with one of similar capacitance and equal or above Voltage rating. These type of capacitors are also polarized so make sure you observe the polarity of the capacitor to be replaced and install new the same way.
The speaker must be removed before you can reach the component side of the chassis, where the electrolytic capacitors reside. Four screws, circled in the picture below, hold the speaker to the chassis.
Once the screws have been removed, you must flip the speaker towards the top of the chassis, where the loopstick antenna is attached, so that you can gain access to the wires. You must desolder the yellow and black wires from the speaker terminal in order to remove.
Circled below in red are all of the electrolytic capacitors that need to be replaced. You must remove the Power/Volume control, circled in yellow, from the chassis to gain access to one of the electrolytic capacitors to be replaced.
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I also took this opportunity to lubricate the shaft of the Power/Volume control as its rotation was quite stiff. I use Labelle 107 Oil as it is safe on plastics and I have it around for my model train hobby.
Below is a picture of the chassis with the electrolytic capacitors replaced. I have circled the replacement capacitors in red. You'll notice that 60 years of development has led to much smaller capacitors packages. I had to change connection locations as I replaced the original axial package electronic capacitors with radial packaged ones that I keep in stock.
Once again I took the opportunity to test my Heathkit XR-1L radio after the replacement of electrolytic capacitors. I used alligator clips to temporary connect the speaker to the yellow and black audio transformer leads. In addition, I used alligator leads to connect a 9 Volt battery, used as a temporary power source. Once powered on, I noticed immediately a drastic improvement in the sensitivity of this receiver. I was able to pick up stations accross the entire AM broadcast band!
Step 3 Disassembly
The chassis of my Heathkit XR-1L radio was pretty rusted and corroded, most likely caused by corrosive chemicals emitted from dead batteries left in the radio many years ago. The only way I could make the chassis presentable again was to sand and then paint it. The first step is to remove as many components as possible from the chassis to make the masking process easier.
I removed the six transistors, they are mounted in sockets. I removed the transistors, one at a time, noting their part number and placement on the chassis.
I removed the side panels, in order to making the paint process easier. Three screws and the Power/Volume control nut must be removed in order to free the right side panel. In addition, you must desolder the solder lug connected to the white wire leading to the battery compartment, then thread the wire through the hole. Once these are removed the right side panel should be free from the chassis.
You must remove several screws on the left side panel in order to free it from the chassis.
You must also separate the adjustable bar from the left side panel. The bar has a insulated battery contact that must be removed for paint as well. It is held in place with one screw. Make note of how the insulators are placed on the screw shank.
The loopstick antenna, circled in red below, must be removed for paint. Plastic mounts on each side hold it to the chassis side plates. I noted the locations were its wire leads are soldered to components on the chassis, then desolder the wires from the antenna.
I decided to also remove the tuning capacitor from the chassis, first noting its wiring before desoldering wires connecting to it.
Next I removed both interstage and audio transformers from the chassis, first, making note of how they were wired to components on the chassis. I took the picture below after I already removed the audio transformer.
Step 4 Sanding and Polishing
It is important to remove as much rust and corrosion from the chassis and side panels as possible before paint. I used my Dremel tool with either a wire brush or sanding drum to remove the heavier rust deposits.
As a final step, all of the chassis parts were wet sanded with ultra fine 800 grit sandpaper.
As I time saving step, I typically replace rusted hardware (nuts, screws, lock washers) with new. It only adds a couple dollars to the cost of the project. Unfortunately, our local hardware store did not have the same style of slotted screws used to assemble the Heathkit XR-1L chassis.
Instead, I used my cordless drill, Meguiar's Motorcycle All Metal Polish, and paper towels to shine the screw heads. I would insert the shaft of the screw in the drill's chuck then tighten it down firmly. I would then apply a dab of polish to the paper towel. I would press the paper towel with polish against the screw head while the drill was spinning. I repeated this process with each chassis screw and was amazed at the results. This made the screws look like new!
Meguiar's PLASTX and an old toothbrush work wonders on cleaning up old knobs!
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Step 5 Masking and Painting
It is important to remove all wax and grease residue from parts to be painted. Just prior to paint, I wipe down all parts to be painted with Prep-All made by the company Klean-Strip. This clear liquid chemical dries quickly leaving no residue.
The first item to be painted was the metal speaker frame. I carefully masked off the speaker cone to prevent overspray then applied Prep-All to remove wax and grease residue. Painting the metal speaker frame required two paint sessions, allowing 24 hours of drying time between them. One session to paint the mounting tabs on the front of the speaker and another to paint speaker frame on the back. I used Krylon Shortcuts Chrome spray paint on the speaker frame. It is available at most craft stores. Please see my slideshow below for a pictorial view of the steps.
On many parts to be painted, I use magnet wire to suspend them. This allows me to paint all surfaces and then let them hang to dry.
I carefully store painted parts so as to prevent them from being scratched. I placed a paper towel at the bottom of a plastic storage bin then place the parts in it so they are not touching.
I painted the main chassis with Dupli-Color HWP101 Silver High Performance Wheel Paint, this paint is durable and has texture which hides surface imperfections. I carefully masked off all components that I didn't want painted. In addition, I masked off the component side of the chassis. I didn't paint the component side of the chassis because many components are electrically grounded to it, paint is not conductive. As before, I suspended the chassis with magnet wire, allowing me to paint all surfaces and then hanging to dry. Please see my slideshow below for a pictorial view of the steps.
Dupli-Color Wheel Paint on Amazon!
I typically use Dupli-Color Wheel Paint when painting vintage radio chassis. This paint is durable and has texture which hides surface imperfections.
The brass mounts that hold the carry handle to the Heathkit XR-1L case were badly corroded. First I lightly sand them and then painted them gold. I used a test lead with alligator clip to hold them while they were being painted.
I used a sharp bamboo stick to paint the dial scales on both the Tuning and Power/Volume knobs. I used Acrylic Enamel Gold paint that I have on hand for my model railroad hobby.
Step 6 Chassis Assembly
First, I had to attached all ground lugs, terminal strips, and speaker standoffs with the original screws, nuts, and lock washers. Four of the screws also server double-duty and hold the audio and interface transformers in place. The screws holding these items in place were removed for paint. Next, I had to solder the wires connected to the audio and interface transformers to the proper points on the terminal strips.
The Tuning capacitor needs to be installed to the left side panel first. Then the side panel can be attach to the chassis with three screws. I had to install a solder lug, circled below, as the painted side panel will electrically isolate the frame of this air capacitor from the chassis. Once the side panel is attached to the chassis, I will run a wire from this solder lug to a chassis ground point.
Here is a picture of the chassis with both left and right side panels attached. The Power/Volume control, circled below, was attached to the right side panel after it was attached to the chassis with three screws. In addition, I installed the loopstick antenna to the top of the chassis.
Time to install the ground connection between the Tuning capacitor and the chassis. I circled in red the soldered endpoints for this connection. At this point I also soldered the rest of the connections to the Tuning capacitor and the loopstick antenna, these connections are circled in yellow. Note: There are other connections to the Tuning capacitor and loopstick antenna on the other side of the chassis that are not displayed in the picture below.
The audio transformer's wires are then soldered to the speaker terminals.
The speaker is mounted to standoffs, attached to the chassis, with screws.
I decided to attach a 9 Volt battery clip to the battery terminals. This allows me to power my Heathkit XR-1L radio by either a 9 Volt battery or six D batteries, as originally intended.
I cut a rectangular piece of packing foam that fits the height and depth of the battery compartment. I then cut a rectangular opening in the center just big enough to hold the 9 Volt battery snuggly. Picture below is the 9 Volt battery in its newly constructed holder.
Step 7 Final Testing and Alignment
It is always a good idea to test electronics before buttoning it back up into their enclosure. In addition, I wanted to check the alignment of this radio as it was built from a kit. The Heathkit XR-1L radio can be aligned without any special equipment. Before performing the alignment, I installed the transistors in their appropriate sockets. Here are the alignment steps I used, based on my experience with Superheterodyne radios. It differs slightly from the official Heathkit XR-1L alignment procedure.
Step 8 Install Chassis
The last major step is to install the chassis into its leather case. First, I treated the leather case with Meguiar's Rich Leather Conditioner. I have many Meguiar's automotive products on hand for use on my automobiles.
The original formed leather handle was missing from my Heathkit XR-1L radio, I assume it rotted away many years ago. I found a suitable guitar amp leather carry handle on Amazon that will do nicely. The replacement leather handle matches the cream color of the Tuning and Power/Volume control knobs.
I cut off the original chrome mounts of the replacement leather handle with a Dremel cut-off saw. I then fashioned handle connecting rings using cloth coated wire painted gold. I then soldered the ends of the cloth coated wire together. The soldered ends will be concealed in the brass mounts attached to the leather case.
The brass mounts that connect to the leather carry handle have clips that pass through the leather case. The clips are then bent over to secure them to the case.
Here is a picture of the replacement leather strap installed.
Finally, the chassis can be installed in the case. It is held in place by two screws. I have circled where the screws are installed.
Here is a picture of my newly restored Heathkit XR-1L.
My newly restored Heathkit XR-1L AM Radio in action!
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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