The GE Model P945B Radio is a 6 Transistor AM Radio first offered in 1964. It covers the AM Broadcast Band.
It is of the Superheterodyne design featuring the following sections:
Mixer/Oscillator - Used to convert AM broadcast band into an IF (Intermediate Frequency) of 455KHz.
IF Amplifiers - Bandpass amplifiers that pass/amplify a narrow range of frequencies in the 455KHz range.
Diode Detector - Removes IF envelope leaving audio output.
Audio Preamplifier - Prevents loading of the IF Amplifier and provides an impedance match to the push-pull audio amplifier.
Audio Amplifier - Efficient two transistor push-pull amplifier used to boost the audio to make it suitable for listening without earphone.
One of the unique features of this radio is its use of a high impedance speaker with reed suspended between 2 pole pieces that drives the paper cone with a stylus. It is directly driven in push-pull by a pair of collectors, without an audio output transformer.
This radio falls under the "vertical shirt pocket" type, although you would need a rather big shirt pocket to contain this radio!
It also has a jack so a high impedance earphone can be used. Below are pictures of the GE radio prior to repair.
Step 1 Obtain Schematic
While you can do some troubleshooting without a schematic, as basically the majority of "shirtpocket" AM radios from the 1950s up until 1980 are built the same. Having a schematic diagram greatly reduces the amount of troubleshooting time as you can quickly identify areas of interest. I was able to find a schematic and component placement diagrams for my model P945B on the RadioMuseum site. Click on the button below to go to the URL.
Step 2 Determine Symptoms
This GE radio requires two AA "Penlight" batteries for power. I installed two fresh batteries then turned the volume knob to the "ON" position. I could not pickup any AM Radio stations no matter how high I turned up the volume or adjusted the tuning dial. In addition, I could not hear any atmospheric noise, that you typically hear in between radio stations, when tuning.
"Build Your Own: Transistor Radios" on Amazon
Step 3 Disassemble
The disassembly process of vintage portable AM radios is much easier than tabletop or console models. The back cover typically just snaps in place for easy replacement of the batteries. You just need to insert penny in the slot at the bottom of the case then twist to liberate the back cover and expose the inner workings.
Only one screw, circled in red below, holds the printed circuit board in place.
The speaker is held in place to the front cover with two tiny bolts. I had to use needle nose pliers to remove. Below is a picture of the printed circuit board and speaker liberated from the case.
Step 4 Troubleshooting
The first thing I determined, by taking a Voltage measurement between the positive and negative power rails, was that the GE radio was not getting power. I should be able to see 3 Volts! Power rails are circuit traces on the printed circuit board used to power all of the different sections of the radio. They are typically located at the outside edges on the foil side. I determined that the issue was that the batteries contacts had a layer of rust on them that prevented a good electrical contact. I used a Dremel wire brush on these contacts until they were shiny then reinstalled the batteries in the right polarity. Success!
The radio was getting power yet my original "no sound" symptom was still there.
Next, I figured I would inject an audio signal at the Cathode of the Detector Diode to determine if the issue is with the audio section. One connection of my homemade audio generator goes to the ground bus, which happens to be positive in this radio due to its extensive use of PNP transistors, and the other side to the Cathode of the Detector Diode, which is the input of the audio pre-amplifier.
Again there was no audio, even with the injection of an audio signal into the audio pre-amplifier. After some investigation, I discovered that the tarnish on the contacts of the earphone jack was preventing a signal from getting to the internal speaker. The contacts are normally closed to allow the audio signal to the internal speaker but open when and earphone is plugged in to divert the audio signal to it. Spraying contact cleaner on the contacts removed the tarnish and finally I could hear the injected audio signal through the internal speaker.
The next issue was that the I would hear static when changing the volume level. I determined that the potentiometer used for audio control was dirty and sprayed a little contact cleaner where the wiper meets the carbon resistive element. I then worked the volume control potentiometer through its full motion until the static was gone.
Contact Cleaner on Amazon!
OK, so I fixed all the issues in the audio section, but I still couldn't hear any atmospheric noise or radios stations. This lead me to conclude there was an issue with the mixer/oscillator or IF amplifier sections. One way to test the IF Amplifier sections is to inject a modulated 455Khz RF signal into the input of the IF amplifier sections using an RF generator. You should hear the audio tone that is modulating the RF carrier if these amplifier are working correctly. In my case there was no audio sound from the internal speaker of the radio so I knew there was an issue with one of the two IF Amplifiers, but which one?
You can use the process of elimination to determine which IF Amplifier stage is at fault. Start by injecting the 455Khz modulated RF signal in the IF Amplifier that feeds the Diode Detector. If no tone is heard from the internal speaker then you know you isolated the bad stage. If a tone is heard, then by process of elimination you know the remaining IF Amplifier stage is at fault. In my case I had determined that the IF Amplifier closest to the Detector Diode was at fault. Now I needed to determine the issue down to component level.
Upon closer examination I noticed that there was a lot of corrosion on the metal shield that enclosed the IF Transformer of the second IF Amplifier. See area circled in the picture below:
I surmised that maybe the corrosion had leaked into IF transformer causing one or more of the ultra tiny wires to break. I few resistance checks told me that I was right! But where do I get an IF Transformer for a vintage AM radio from 1964, surely it would be made of "Un-Ob-Tainiam" and was impossible to get. Upon further examination it looked just like the IF Transformer from a bread-boarded AM radio kit from the 1980s I was about to scrap. The IF Transformer from the 1980s radio was exactly the SAME! Nothing in IF Transformer construction changed in over 20 years. The soon to be replacement IF Transformer is circled in red below.
This GE radio sprang to life once the IF Transformer was replaced and batteries were install. AM Radio Stations now came in loud and clear!
Step 6 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 electrolytic capacitors that are over 50 years old! This GE radio employed three electrolytic capacitors. All electrolytic capacitors should be replaced with one of the same or slightly greater capacitance and working voltage rating. I replaced the electrolytic capacitors circled in red in the picture below:
Below is a picture of all of the parts replaced in this vintage GE radio. The IF Transformer was so corroded that it crumbled when removed from the printed circuit board!
Electrolytic Capacitor Kits on Amazon!
Step 7 Detailing
The front and back cover and knobs of the radio were dirty and the plastic had yellowed. In addition, the vinyl carry case with strap was embedded with years of grime and had yellowed as well. It was AMAZING how well all of the parts looked after being cleaned with "Mr Clean Magic Eraser", the sponge looking thing at the bottom of the picture.
A toothbrush works good for cleaning dirt in grooves and holes in the speaker grill section. Plus your vintage radio is guaranteed not to get cavities!
I used solder flux cleaner to remove the original flux from the foil side of the printed circuit board and the new flux caused by the replacement of the IF Transformer.
Take a look at the results of cleaning the printed circuit board, vinyl cover, and plastic radio case! See below:
Step 8 Reassemble
Perform the steps in the "Disassemble" section in reverse order to put the GE radio back together.
The finished repaired GE radio!
My Vintage GE Model P945B Radio in Action!
As an amateur radio enthusiast, I have found on several occasions that it would have been handy to have a frequency counter available in my arsenal of test equipment. But, like most amateur radio enthusiasts on a budget, I could not justify spending hundreds of dollars on said equipment. In addition I wanted a frequency counter to help with the analog dial alignment process on my vintage Kenwood TS-520S SSB Transceiver. In order to save money I decided to look at Kit Based or Build Your Own options.
Kit Based versus Build Your Own
There are plenty of frequency counter kits online. Some from reputable kit providers such as Canakit, others from providers of dubious reputation. Most kits I did find online have a limited frequency range, typically only up to 2Mhz. I also know that it is much easier to build a frequency counter these days because much of the old logic circuitry can be replaced with a single PIC microcontroller. After searching online with Google using "PIC base frequency counter" as the search phrase, I found the perfect solution for me. It was a PIC based frequency counter build by amateur radio enthusiast Wolfgang "Wolf" Buscher (DL4YHF). Wolfe claimed that his PIC based frequency counter had a frequency range of 1Hz to 50Mhz with only a handful of parts! This sounded like a perfect solution for me!
Giving credit where credit is due!
The PIC based frequency counter that I describe and build in this lens is not of my own design. It was based on a design by amateur radio enthusiast Wolfgang "Wolf" BÃ¼scher (DL4YHF). Wolf designed the circuit and created the firmware to be installed on the PIC microcontroller used in this circuit. Click here to visit Wolf's site. What I do bring to the table is, in my opinion, an easier to read schematic and complete parts list with parts numbers sourced from Jameco electronics. In addition, I provide high resolution pictures of the assembly of my frequency counter.
My updated schematic and parts list
Unfortunately you cannot see the pin numbers on the 16F628 when I converted the Visio schematic to JPG. I can provide this schematic in PDF format.
SW1 is a slide switch that controls power to the frequency counter. REG1 drops the battery voltage from 9 volts to a steady 5 volts. C2 acts as a decoupling capacitor and is used to reduce noise from the power supply. C1 blocks DC from entering the amplifier circuit consisting of R2, R3 and Q1. Q1 feeds the amplified input to pin 3 of the 16F628.
The firmware programmed into the 16F628 allows this PIC microcontroller to perform the necessary logic functions to convert the frequency of the input signal to a format readable on the 7 segment displays.
The firmware programs pin 3 as an input port. The circuit consisting of R4 and SW2, a momentary switch, allows you to enter a program function where you can set or remove a frequency offset. When pin 4 goes low, the 16F628 goes into offset program mode. C3, C4 and X1 form a resonant circuit used to provide a timing signal to the 16F628.
Pins 6, 7, 8, 9, 10, 11, 12, 13 of the 16F628 are programmed by the firmware to be output ports. They are connected to current limiting resistors R5 through R12 and drive specific segments of the 7 segment LED readout. The 16F628 firmware is setup to multiplex the output to the LED display, only one 7 segment digit is on at a time. The multiplexing happens so fast that all five 7 segment digits appear to be on at the same time.
Multiplexing of the 7 segment displays are handled by pins 1, 2, 17, 18 of the 16F628. These pins are also set up as output, when output is low one or more segments of a specific digit will be lite. There are not enough output pins on the 16F628 to directly allow a fifth digit to be multiplexed so the circuit designer came up with a creative way to drive this digit. The fifth digit lights when when Q2 is in the on state. Q2 is triggered when pins 1, 2, 17, 18 of the 16F628 are a logic high. D2, D3, D4, R13, and Q2 effectively form a four input NAND gate. D1 prevents Q1 from conducting if the base-emitter voltage is less than the forward voltage of the other diodes.
Programming the PIC microcontroller
Before you build the frequency counter circuit, you need to load the firmware into the 16F628 microcontroller. This is accomplished with a PIC programmer. While there are many plans for PIC programmers on the Internet, I recommend purchasing the Canakit CK1301 kit. It is fairly inexpensive (under 40 US dollars) and connects to your computer by USB connection where most do-it-yourself PIC programmers still require a serial port. How many computers these days are still equipped with a serial port? Owning a PIC programmer is a must for electronic hobbyist these days as many projects revolve around the inexpensive PIC microcontroller. The instructions that come with the Canakit CK1301 kit tell you how to build the PIC programmer, install the Microchip MPLAB software on your computer, and how to do initial testing. Simply insert a 16F628 PIC microcontroller into the socket making sure pin 1 is properly oriented, click here to download the firmware from Wolfgang Busher's site. It should be contained in a file called freq_counter.zip Open this Winzip file and copy the counter2.hex to your desktop. This is the firmware required for this project. Open PICKit 2 Programmer Software then choose File form the menu then Import Hex from the drop-down menu and point to the counter2.hex file on your desktop then choose Open. Click on the Write button, the firmware should be uploaded to the 16F628. You can remove the programmed 16F628 from the programmer as the firmware has been installed.
PIC Programmer kits on Amazon
I used the CanaKit CK1301 PIC programmer for this project. It was easy to assemble and worked great!
My first rule of thumb when building a new circuit is to always build it on a breadboard first before committing to a more permanent media such as perfboard or printed circuit board. You will find plans and schematic diagrams on the Internet that simply do not work. There is no governing body for schematics posted on the Internet so it is "Hobbyist Beware". Luckily this circuit performed exactly as the creator described. Check out the frequency generator in the lower left-hand corner, I built this while I was a junior in high school. It is ready for a "Extreme Project Makeover"........maybe a new case and some shiny knobs!
Committing the Frequency Counter to a Printed Circuit Board
OK, so the frequency counter circuit worked on the breadboard. Now it is time to commit it to a printed circuit board. I like to use Radio Shack (Model 276-170) printed circuit boards because it closely matches the layout of my breadboard. This makes it easy to transfer the circuit from breadboard to printed circuit board. I use a dab of hot glue to keep all of the wiring in place.
Once committed to the printed circuit board you need to re-test the frequency counter. This time I tested the circuit by connecting it to the VFO output of my vintage Kenwood TS-520S SSB Transceiver.
Finishing the project
Now it's time to complete the frequency counter project by mounting the printed circuit board in an enclosure. I use small crafted wooden boxes that I find at our local craft store. They are certainly much more pleasing to the eye than the drab black and blue plastic boxes intended for this purpose. The next step is to drill the holes for the switches, for mounting the frequency counter printed circuit board, the 9 volt battery clip, and the input terminals. At this stage I also gather all of the screws, nuts, lock washers and other hardware required to finish the project. You can see in the picture that all of the hardware needed is in the red sandwich keeper above the wooden box.
Finishing the wooden craft box
The wooden craft boxes from the local craft store are unfinished. I like to put a couple coats of clear polyurethane on them so that you can still see the natural beauty of the wood. First I use a pencil eraser to remove all of the pencil lines on the box that I used to mark holes for drilling. Then I take a fine grit sandpaper and carefully hand sand the box until all of the saw and routing marks have been removed. Save yourself some time and only sand the outside of the wooden box, the only time you will see inside the enclosure is when you are replacing the battery. I typically put two coats of polyurethane on the wooden box, sand the outside with an ultra fine grit, wipe all of the sanding residue of off the enclosure with a clean damp cloth, then apply the final coat.
Final Assembly - Mounting the Frequency Counter Printed Circuit Board
Time to mount the frequency counter printed circuit board, I use four long mounting screws to secure it to the front cover. I use two nuts per screw on the back to adjust distance between the printed circuit board and the display hole in the front cover. In addition, I mount the momentary program and power slide switch. I use a dab of gold paint on the screw heads so that it matches the copper hinges and clasps that were included with the wooden box.
Final Assembly - Mounting the battery holder and regulator board
The last step is to mount the Fahnestock clips for the measured frequency input, the 9 volt battery holder, the regulator printed circuit board then connect the wiring. I salvaged a perfboard with a LM7805 regulator on it from a now defunct model railroad project. You can mount the regulator directly to the frequency counter printed circuit board. I then connected a 9 volt battery clip to the input of the regulator board and attached the output to the slide switch. You must also connect the push button switch to the negative output of the regulator board and to pin 3 of the 16F628.
Opps, I see an issue with my wiring. Can you see the mistake?
The mistake is that the power slide switch is on the positive output side of the regulator board. It should be on the positive input side. The problem with my wiring is that the regulator is consuming a small amount of current even when the power switch is off. I will need to correct this problem.
Location of the input terminals
I mount Fahnestock clips on the side of the enclosure, these terminals are to be connected to the input signal for frequency measurement.
Time for final testing before connecting it to a test signal. Upon power up, you should first see all segments of the five 7 segment digits light as a test then a 0 will show up in the fourth digit from the left. When you press the button you will be placed in program mode you will see "Prog" on the display. Please click here to read find out more about the adding or subtracting the frequency offset. Please note: A flashing decimal point indicates the display reading is in kHz, a steady decimal points indicates the reading is in Mhz.
My frequency counter connected to my vintage Kenwood TS-520S
I connect the frequency counter to my Kenwood TS-520S VFO output in order to calibrate the analog dial. When the dial is properly calibrated (on any band), the frequency counter should read 5.5Mhz when both main and subdial are at zero. Make sure you use the proper pointer for SSB(Single Side Band) or CW(Continuous Wave). There are pointers for Lower Sideband(LSB), Continuous Wave(CW), and Upper Sideband(USB).
The Frequency Counter in Action!
You too, with a minimum number of parts, can build a working frequency counter using a PIC microcontroller. Just follow this instructive Hub!
PIC Books on Amazon
I own this book. It covers Arduino and Piacaxe projects related to Amateur Radio. One of the coolest projects in this book cover how to build an Antenna Analyzer, which is typically a costly tool for an Amateur Radio enthusiast.
Electronics has always been in my blood!
Electronics has always been a passion of mine. In grade school I used to make circuits with batteries, switches, and motors. In 7th grade science class we actually got to build a single wet cell battery and perform different experiments with it. I chose Vocational Electronics as an elective in my Junior and Senior year of high school. I also experimented in electronics workshop, located in my parents basement, which consisted of an folding table, soldering iron, Radio Shack Micronta 8 Range Mulitmeter, and an old Eico Model 460 Oscilloscope my Uncle, who was an Electrical Engineer, gave me.
The GM HEI Ignition Coil
I decided in 1986, my Junior year in High School, that I was going to build a High Voltage Project using the salvaged HEI Ignition Coil. Below is my completed project. I will go through each aspect of this project in this blog.
Below is the GM HEI Ignition Coil as it looks removed from the Distributor Cap. It is secured by nails at the corners to the wooden base. The center of the HEI Coil is the High Voltage output. I use part of a spring metal battery clip to secure the wire from the High Voltage output to the electrode in place.
I used an IRF250 N-Channel MOSFET Transistor, in a TO-3 style package, to pulse the direct current to the primary winding of the HEI Ignition Coil. Originally I was using three 2N3055 NPN Bipolar transistors in parallel to do the job but found that the specs varied slightly with the transistors and one was doing more work than the others and getting very hot to the touch. I found that the IRF250 MOSFET did a better job than the three bipolar transistors and didn't get as hot due to its very low resistance between Source and Drain when switched on. The picture below shows the three transistor mounts on the aluminum heat sink with only the single IRF250 MOSFET Transistor remaining.
A 1N1007 Rectifier Diode is placed in parallel with the Source and Drain of the IRF250 MOSFET. Normally it is reverse biased but it does conduct the counter EMF current caused by the magnetic field collapsing in the Primary winding of the HEI Ignition coil. The 1N1007 purpose is to protect the IRF250 MOSFET from this large counter EMF Voltage. This counter EMF Voltage is several magnitudes larger than the input Voltage.
Evil Genius Books on Amazon
I enjoy the "For the Evil Genius" book series. A lot of my inspiration as a teen came from a book called "Build Your Own Laser, Phaser, Ion Ray Gun and Other Working Space Age" the author, Robert Iannini, later went on to write several books in the "For the Evil Genius" book series.
My Ignition Coil High Voltage Experiment is powered by conventional 120 Volts AC line current. The transformer below drops the line Voltage from 120 Volts to 24 Volts AC.
The Rectifier and Diode assembly below take the 24 Volts AC and convert it to roughly 30 Volts filtered DC, under the load of the HEI Ignition Coil. The HEI Ignition Coil was designed for 12-15 Volts input Voltage and I am pushing the envelope by doubling it.
The perfboard on the right contains a separate Capacitor/Diode assembly used to convert AC to a filtered DC to run the Oscillator perfboard located to the left. The Oscillator board drives the IRF250 MOSFET Transistor used to pulse the DC to the Primary winding of the HEI Ignition Coil. The Oscillator perfboard consists of the 555 Timer IC as the Oscillator, an LM324 Voltage Regulator used to provide a consistent 5 Volts DC to the timer circuit. In addition, there is a driver transistor at the bottom used to control IRF250 MOSFET Transistor and not load down the Oscillator circuit.
A second transformer, circled below, converts conventional 120 Volts AC line current to 6.3 Volts AC which is used to power the Oscillator circuit.
I created a little control panel out of a piece of scrap steel bent at right angles, then primed and painted it green. The control panel consists of an on/off slide switch that controls power, a neon power light, and a potentiometer that controls the oscillator frequency from 20 to 20,000Hz.
Below is the "Test Chamber" I created. The distance between the electrodes are adjustable by adjusting the brass nuts. At one time the Test Chamber had a lid on it but it melted when the material, that I was testing its insulating properties at High Voltage, caught fire and melted it. I shouldn't have used a plastic box as the Test Chamber but it was the only insulted box structure I had at the time.
Striking a plasma arc in the test chamber! The plasma arc does strange things when the input Voltage to the primary is modulated at 15,000 Hz. At this frequency, the electrical arc leaps out and forms circular and even "U" shaped arcs. I speculate at around 15,000 Hz I reach resonance of Ignition coil/electrode circuit. Typically you need an LC (Inductive and Capacitive) circuit to achieve resonance. I suspect the capacitive aspect of the circuit comes from either the internal capacitance between the copper windings in the HEI Ignition coil or the capacitance between the electrodes. I am wearing thick blue insulated gloves and safely glasses during initial operation as I don't know what to expect from this project that has been dormant for 29 years!
My Vintage Ignition Coil High Voltage Experiment in action!
A Brief History of Arvin Industries
Arvin Industries started out as the Indianapolis Air Pump company in 1919, their first product was a reliable air pump used to inflate automotive tires.
In 1927, they changed their name to Noblitt-Sparks Industries and sold "Arvin Heaters" which were specialized heaters used in the automotive field. Back in the day most cars were not equipped with heaters. By the 1930s, Noblitt-Sparks had diversified into making radios for the automobile industry. In addition, they made Silvertone branded radios for Sears.
In 1950, Noblitt-Sparks changed their name to Arvin Industries. While still a leading automotive supplier, they branched out into consumer electronics and appliances. My Arvin 33R78 Stereo Radio was built in 1963.
Arvin Industries left the consumer electronics and appliance market in the early 1970s but still has as a reputation for building quality products in Automotive and Research & Development fields.
My Arvin 33R78 worked perfectly back in 1985. But slowly over time it developed an annoying AC hum as the electrolyte in the power supply capacitors dried up. Recently the FM Mono and Stereo modes of the radio ceased to work altogether which made me think it was time to do a full restoration on this marvelous old radio.
****Caution Electrical Hazard****
The Arvin 33R78 Stereo Radio does not employ a transformer to isolate the AC line current from the chassis. AC Power directly out of the wall is rectified/filtered and used for the B+ Voltage for the vacuum tubes. Tube filaments are configured in series so as to drop the line voltage to the proper voltage levels for the vacuum tubes.
Transformerless designs, as used in the Arvin 33R78, had a metal chassis connected to one side of the power line. While the user is perfectly safe from electrical shock due to the insulated cabinet and knobs, you need to take extra precautions when servicing the radio when removed from the cabinet.
FIRST UNPLUG THE ARVIN RADIO FROM THE AC OUTLET! Speakers are removable and come with long speaker cords. Unwind the speaker cords and unplug from the Arvin Stereo.
Remove left and right speakers from the wooden cabinet and set aside. Also remove the knobs from the front of the Arvin Stereo.
Remove the four screws that hold the back cover onto the wooden cabinet.
Notice that the internal speaker wires are soldered to jacks on the back cover and that the electrical cord is disconnected when the back cover is removed.
You have to remove several screws from the bottom of the cabinet in order to remove the chassis.
Two nuts on the left side hold the chassis to the front of the cabinet, the second one is directly below the one circled in the picture.
Two nuts on the right side hold the chassis to the front of the cabinet, the second one is directly below the one circled in the picture.
I recommend unsoldering the internal speaker wires from the back cover then insulating the exposed ends with electrical tape or wire nuts. It is easier to work on the chassis with the back cover out of the picture.
Make sure you unsoldering the second pair of internal speaker wires and insulate the ends as well. The yellow speaker wire just came off without unsoldering. Possibly a cold solder joint.
Finally the chassis is free and clear of the wooden cabinet.
Cleaning and Lubrication
Notice the poor repair job someone did when replacing an electrolytic capacitor.
Here is the chassis and printed circuit board fresh out of the wooden cabinet. Notice how dusty and dirty.
Here is the chassis and printed circuit board after I cleaned it with compressed air. Much better looking!
I used contact cleaner to clean the contacts in the variable resistors. There is a small opening next to the terminals of the variable resistors that you can spray contact cleaner into.
I use Labelle 109 model train oil to lubricate the shafts of all variable resistors.
Make sure you lubricate the pulleys for the dial indicators!
Test Vacuum Tubes
Electrolytic Capacitor Replacement
C2A (80uF), C2B (30uF) and C2C (40uF) are all housed in the metal cylinder circled in the picture.
You must jumper together where the grounding tabs of C2 where connected to the printed circuit board. C2C was replaced with a discrete 47uF 25Volt Capacitor as seen in the picture. Make sure you get the polarity correct!
C2A was replaced with a discrete 100uF 150Volt Capacitor, C2B was replaced with a 47uF 150Volt Capacitor. Once again, make sure the capacitors are polarized correctly.
C1 (120uF) was replaced with 220uF 150Volt Capacitor. Get the polarity right!
Don't forget to replace C3, a tiny 4uF capacitor towards the front left of the printed circuit board. I replaced this capacitor with a 4.7uF 50Volt capacitor.
Testing and Troubleshooting
As mentioned, the chassis of the Arvin 33R78 is "hot", meaning it is connected directly to the AC Line. Care must be taken when testing and troubleshooting. When working on a electronic equipment with a hot chassis, I always wear rubber soled shoes and use the old tried and true practice of sticking one hand in my pocket and using the other hand to manipulate test leads and switches. I also recommend attaching the insulated knobs to the shafts of the front controls. Disconnect the power before making any changes to the chassis or the printed circuit board!As you can see from the picture, I used test leads to connect the cabinet speakers to the audio transformers mounted on the chassis.
Get the Arvin 33R78 Stereo Radio Schematic
Arvin 33R78 Stereo Radio SchematicThe Arvin 33R78 Stereo Radio Schematic with parts listings and troubleshooting documentation is available from SAMs Photofact for around $20.
The Arvin 33R78 Chassis ready for testing and troubleshooting.
Testing the Arvin 33R78 Chassis
Cleaning up the wooden cabinent
Arvin 33R78 cabinet before cleaning and polishing.
Look how nice the cabinet looks after several applications of Old English Lemon Oil.
I even treated the inside of the cabinet to the a good cleaning and some Old English!
Cleaning the Knobs
Here are the knobs before cleaning.
An old toothbrush is the best tool to clean between the ridges of the knobs. It also prevents the knobs from getting tooth decay!
Here is a picture of the freshly cleaned knobs.
Installing the chassis back into the cabinet is just the opposite of removal.
Make sure you properly fasten the chassis into the cabinet. If a fastener or screw is missing get a replacement from your junk box or local hardware store.
You may need to use a Dremel to cut the shaft lengths of replacement screws.
Make sure you solder the left and right channel speaker connections back to the terminals on the back cover.
The back cover back in place and the speaker wires neatly wound around their caddy.
My restored Arvin 33R78 Stereo Radio in Action!
The restoration of this vintage Arvin 33R78 Stereo radio was most gratifying. It took my mind off of the stresses of my daily job and reminded me of a simpler time when people had the time to sit around and listen to the radio for enjoyment.
Radio Restoration Books On Amazon
I consult books often during radio restoration. I grew up in the transistor and rectifier era and these books taught me a lot about vacuum tube and selium rectifier technology.
The Yaesu FT-1900R is a 2 Meter FM Transceiver that is capable of up to 55 Watts transmit power. This radio is setup for mobile use and requires 12 Volts 11 Amps to power it. With the addition of a bench DC (Direct Current) power supply, this transceiver would be at home in any Ham Shack.
I myself am a newbie and I ordered the Yaesu FT -1900R from Amazon as my very first radio once I got my Technicians License. Once ordered, the radio showed up two days later as I am subscribed to Amazon Prime and get automatically upgraded to two day shipping.
Upon opening the package, I was immediately impressed with FT-1900R. The body of the radio is one massive heat-sink eliminating the need for a noisy fan to keep it cool. There is a minimal number of switches on the front, this was accomplished by using menus to change different parameters of the radio that are not accessed often. I immediately attached the radio to a DC bench power supply and to an Arrow J Pole antenna I mounted in our attic and was able to pick up multiple transmissions.
The manual was easy to understand, it took me about five minutes to set the PL Tone and to save my first repeater frequency into memory. I then proceeded to store a couple of other repeater frequencies. You can store up to 200 frequencies in memory. One of the great features of the FT-1900R is that you can scale back on the transmit power, by default it transmits at 55 Watts. I can see that it would be important to scale back transmit power if you are running off of a battery in an EMCOM (Emergency Communications) situation and need to get the maximum battery life.
The buttons on the front of the FT-1900R and on the microphone are illuminated for easy nighttime use. You can also recall frequencies in memory from the illuminated keypad on the microphone which would be ideal for mobile operation. On an hour long rag-chew, transmitting at 55 Watts, the case of the FT-1900R does get hot to the touch. I believe the aluminum chassis was designed this way to dissipate heat. The receive audio is very clear audio and all repeater contacts indicate that they can hear me clearly.
There are some features, such as WiRES-II, which would appeal to the more seasoned Amateur Radio Operators. WiRES-II allows you to communicate by Amateur Radio and the Internet.
The FT-1900R was a great purchase and I definitely recommend this radio to any amateur radio enthusiast.
Video of Amateur Radio operator using his FT-1900R to listen to transmissions from the International Space Station as it hurtles by overhead!
As any owner of a Kenwood TS-520S can attest to, it is a real pain to calibrate the analog tuning dial so that the frequency read is the truly accurate. The process involves changing the function switch to CAL-25kHz, this is an internal reference signal, then you turn the main tuning knob until you zero beat the the internal reference signal, adjust the dial scale until it shows the correct reading. In order to maintain turning dial accuracy, you have to do the dial calibration again when changing bands or modes of operation (Upper Sideband, Continuous Wave, Lower Sideband). I thought it would be cool to eliminate all of this calibration nonsense by adding a digital frequency counter to the to the TS-520S so that you always have the tuning frequency accurately displayed.
Video showing the process of zero beating for dial calibration against station WWV
Easier procedure for analog dial calibration by K4TFJ
The Bad News
One of my goals was to provide a readout of the current tuning frequency on the frequency counter but it does not look it is quite that simple. I am not sure what "Magic" the DG-5 does to directly perform a readout of the tuning frequency. It somehow does this while monitoring the signals of the CAR OUT, HET OUT, and VFO OUT jacks on the back of the TS-520S.Here are the outputs and their frequencies:VFO OUT: Same frequency variation not matter what the setting of the Band Switch.With both the Main Tuning Knob and Sub-dial set to 0: 5.5MHZWith the Sub-dial set to 600 and the main tuning dial set to 0: 4.9Mhz CAR OUT: Constant 3.2987Mhz no matter where the tuning dial or Band Switch are set.HET OUT: Changes with the Band Switch setting:1.8 - 10.693MHZ3.5 - 3.1239Mhz7 - 15.893MHZ14 - 22.892MHZ21 - 028 - 028.5 - 0I have not yet solved this riddle.
The Good News
If you connect your frequency counter to the VFO OUT on the TS-520S, with some simple math you should be able to determine the true tuning frequency.For you consideration:With both the Main Tuning Knob and Sub-dial set to 0: 5.5MHZWith the Sub-dial set to 600 and the main tuning dial set to 0: 4.9Mhz 5.5MHz - 4.9MHz = 600kHzFormula:True Tuning Frequency = Band Switch + + 100kHzFor example, if the Band Switch is set to 7 and frequency counter reading is 5.200MHz, the true dial frequency is:7MHz + 200kHz + 100kHz = 7.300Mhz
Connecting your Frequency Counter to the TS-520S VFO Output
I use a short video cable with RCA jacks on the ends to connect my frequency counter to the VFO Output on the back of the TS-520S. I removed the RCA jack from one of the cable ends, stripped the insulation back and separate the outside braid from the internal conductor. I then tinned the ends of the outside braid and internal conductor so that they would not come unwound and connected them to the Fahnestock clips which serves and input terminals to my frequency counter. See area circled in the above picture.
The Frequency Counter in Action!
Adding a PIC based frequency counter is a great way to calibrate your tuning dial and provide digital accuracy to your vintage Kenwood TS-520S SSB Transceiver.
What is a Nixie tube?
A Nixie tube is an electronic component used to display a fixed set of characters, typically letters or numbers. It looks like a vacuum tube but functions more like a neon lamp. The tube has one anode or positive terminal and several cathodes, one for each character you want to display. Individual characters can be displayed by applying 170 volts DC between the anode and one of the cathodes. A current limiting resistor of around 47K is required between the anode of the Nixie tube and DC power supply. Each Nixie tube only requires a few milliamps to work. The Nixie tubes I used for this project are Russian made Type IN-12A . This Nixie tube uses an inverted 2 to display 5, most likely to reduce manufacturing costs. A Nixie tube typically displays characters in an orange or reddish glow around the character shaped cathode.
Where do I get Nixie tubes?
Where do I get the rest of the parts for the project?
Most parts like resistors and capacitors I already had. Most vendors require a minimum order when you order discrete components. So say I only need one 1Meg Watt resistor for a project. I would have to purchase at least ten to meet their minimum requirement.
Giving Credit where credit is due!
The Nixie Clock discussed in this Lens is not of my own design. It is based on schematics from Mike Harrison in the UK. My creativeness was used in the implementation of Mike’s Nixie Clock design. Below is the web link to his site.
Caution, only experienced electronic hobbyists should attempt to build this circuit!
My Isolation Transformer:
The Division Bell:
I broke the Nixie clock circuit up into five circuit boards:Power Supply board - provides the necessary voltages to the other circuits.Lower Digit Board - Drives the Nixie tubes that display seconds.Upper Digit Board - Drive the Nixie tubes that display minutes and hours.Colon Driver Boards - There are two of them, these drive neon bulbs to blink at a 1HZ interval to act as the colons between hours, minutes, and seconds.
Power Supply Board Build:
Power Supply Board Testing:
Nixie Tube Testing:
Digit Board Assembly:
Building the Lower Digit Board:
Lower Digit Board Testing:
Building the Colon Driver Board:
Colon Driver Board Testing:
The Display Case:
Nixie Tube Mounting:
Nixie Tube Mounting (Continued):
Addition of resistors to the Digit boards: - I needed to find a place for the 33K resistors that connect to the Base of the driver transistors. The driver trans
Upper Digit Board (Added 33K resistors are circled in red)
Machining the Display Case Base:
Mounting the Nixie Driver Transistors:
Wiring the Time Set Switches:
Wiring Phase 1:
Testing Phase 1:
Wiring Phase 2:
Testing Phase 2:
Electrical Isolation Test:
Complete! - Here are pictures of my completed Nixie Clock with the plastic display cover installed. I use four brass set screws to keep the cover in place. I lo
Video of my Nixie Clock in action!
Building an AM Radio kit is a staple of many Vocational Electronic programs. It teaches radio and electronic theory, soldering, construction, troubleshooting, and the use of test equipment such as Multimeters, Signal Generators, and Oscilloscopes. The two year vocational program I attended in high school was not any different. In 1986, year one in the vocational electronic program, I assembled this Graymark Model 536 Superheterodyne on the foam breadboard provided.
You can still see the instructor's initials on the breadboard in the above photo as he authorized the continued construction after checking my assembly work and measurements. To breadboard was a far as this AM Radio kit made it as that was all that was required in the vocational program as we had to move on to the next topic, Digital Circuits. We were only graded on an operation AM Radio assembled on the breadboard and left to our own devices to transfer the electronic parts from the breadboard to printed circuit board and mount it in the enclosure in order to complete the assembly.
This Graymark Model 536 kit has moved with me on three separate occasions from my parents house, to a rented duplex, and then two homes I have owned with my wife. During the moves I have lost some small parts included with the kit and will need to improvise during the final assembly process.
In 2016, I have vowed to complete this kit with the electronic components ported over to the printed circuit board then mounted in the enclosure provided.
Actually, there is more work to be done than just transferring parts from the foam breadboard to the printed circuit board. Like on the breadboard, you mount components for each subsystem first then perform measurement and calibrations. The final assembly is roughly broken down into Audio Amplifier, Mixer/Oscillator, IF (Intermediate Frequency), and Detector subsystems, each with their own testing, calibration, and measurement procedures.
Stay tuned, as a future blog of mine will give a detailed description of the final assembly of this Graymark Model 536 kit.
Radio Kits on Amazon!
My Graymark Model 536 AM Radio Kit on Breadboard!
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
Copyright © 2017
Radio Boat Anchor
This page and all the pages on Radio Boat Anchor generate income based on an affiliate relationship with our partners including Zazzle, Amazon, and Google. Prices listed are subject to change without notice.