My Father's Stereo
About the Heathkit AJ-10
The Heathkit AJ-10 was offered in the 1960-1961 Heathkit catalog as an economy AM/FM Stereo Tuner kit at a price of $59.95. Actually, the AJ-10 enclosure houses a complete and separate AM and FM tuner with the only commonality is that both AM/FM sections share the same power supply. While being boasted as being a AM/FM Stereo Tuner kit it would be more appropriate to labeled as "FM Stereo Ready". An external multiplexer, such as a Heathkit AC-11, is required to separate A and B channels. Despite being marketed as an "economy" model, the AJ-10 did have advanced features such as magic eye tubes for both bands to aid in tuning. In addition, it offered AFC (Automatic Frequency Control) to aid in keeping the tuner locked into the desired FM channel and prevent frequency drift. In AM mode, the AJ-10 had an internal loop antenna and a bandwidth switch to aid in selectivity.
Caution Electrical Hazard
Like most vintage vacuum tube equipment, the AJ-10 Tuner employs high B+ voltages exceeding 100 volts DC which is used to power the vacuum tubes. Care must be taken when working around this equipment while it is powered on with the covers removed. I always wear rubber soled shoes, work on a bench that has a plastic insulated top, and only use one hand when taking measurements or making adjustments.
Step 1 Remove Top and Bottom Covers
Turn the AJ-10 Tuner upside down, remove the four screws circled in red then slide chassis out of the top cover.
The bottom cover is secured with two screws circled in red.
Top view of the Tuner chassis.
Bottom view of the Tuner chassis.
Step 2 Vacuum Tube Testing/Replacement
Unlike solid state transistors and integrated circuits, vacuum tubes have a finite life span. As they age, fewer electronics are released from the cathode making them less efficient. In addition, the tube filaments burn out much like the filament in a light bulb.
All of the vacuum tubes in the AJ-10 Tuner were original. I can tell because they are Heathkit branded.
Test each vacuum tube in the AJ-10 Tuner. Replace any tubes that are defective or weak.
Step 3 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 AJ-10 Tuner!
Step 3a - 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 1960s. 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.
View of the multi-section capacitor, circled in red, in the AJ-10 Tuner from the top of the chassis.
You must first un-solder all of the connections at the bottom of the multi-section capacitor before you can remove it from the chassis.
Two nuts, circled in red, hold the multi-section capacitor to the chassis.
The multi-section capacitor removed from the chassis. The side of the aluminum can indicates capacitance and working voltage of the internal capacitors.
The guts of a multi-section capacitor. I use needle nose pliers to un-crimp the bottom of the aluminum can exposing the innards. I always wear nitrile gloves when working with the guts of capacitors as the electrolyte may cause skin irritation.
The new replacement capacitors soldered to the multi-section capacitor base. I use a dab of hot glue to secure them in place.
This is a good time to check the two rectifiers connected to the base of the multi-section capacitor. Resistance should be high in one direction and low in the other when your meter is in Diode check mode.
You must re-solder all of the connections to the base of the rebuilt multi-section capacitor after it is once again mounted to the chassis. I also replaced two electrolytic capacitors, circled to the right, that connected to the multi-section cap.
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.
This is how the multi-section capacitor's aluminum can looks like after cutting and smoothing with fine grit sandpaper.
I use hot glue to affix the aluminum can over the replacement capacitors connected to the multi-section capacitor base.
Step 3b other Capacitor Replacement
All other electrolytic capacitors should be replaced with one of the same or slightly greater capacitance and working voltage rating.
Here is a picture of the other capacitors replaced in the AJ-10 Tuner.
Step 4 Cleaning and Lubrication
It is important to clean mechanical switch contacts and lubricate moving parts. Cleaning the chassis is not required but adds aesthetics to the AJ-10 Tuner.
I spray contact cleaner into all switches then work the switch back and forth to clean the internal contacts.
I also spray contact cleaner into the innards of potentiometers and rheostats then work them through their full motion of movement.
I use Labelle 107 model train oil to lubricate pulley shafts and other mechanisms. This oil will not harm plastics.
I use Labelle 106 model train grease to lubricate the bearings of the variable capacitors. This grease will not harm plastics.
Q-tips swabs moistened with Windex work great for cleaning hard to reach areas on the top of the chassis.
I also use Windex moistened Q-tips to clean the bottom of the chassis as they have the ability to clean between wire and electronic components.
I used Windex and paper towels to wipe away years of tobacco residue. This started out as a white paper towel.
Mr Clean Magic Eraser works great for cleaning up the original power cord!
I use Meguiar's Motorcycle Wax to bring back the luster of the AJ-10 Tuner's case.
A toothbrush works great for cleaning up the knobs. Plus the AJ-10 Tuner will not get cavities ;-)
The original sticker on the bottom of the tuner enclosure dried up and fell off the tuner years ago. I copied a picture of the connections from the manual and taped it to the bottom.
Step 5 Testing and Troubleshooting
The Heathkit AJ-10 Tuner Manual has an extensive testing and troubleshooting section at the end of the assembly manual. The FM section of the AJ-10 Tuner comes pre-aligned from the factory and does not require any adjustment. Only a slight bit of alignment needs to be done on the AM section. An RF generator will be required to perform these steps.
Picture of my workbench area.
The first step is to check the power supply voltages against the schematic in the manual to make sure they are within spec. I also check the voltages on each pin of the vacuum tubes to make sure they are the same as on the schematic.
My tuner alignment setup. I use the short wave receiver in the background set to the AM broadcast band to check the frequency accuracy of my vintage Eico Model 325 RF Signal Generator.
You use the screws on the AM turner variable capacitor to adjust trimmer capacitors in order to calibrate the AM dial.
I connect an audio amplifier to the output ports an use test leads for an antenna to perform initial testing to see if I can pickup AM and FM signals.
Final testing is accomplished by connected the Heathkit AJ-10 tuner to my Heathkit SA-2 amplifier and see how it sounds.
Step 6 Assembly
Follow "Step 1 Remove Top and Bottom Covers" section in reverse order to reinstall the top and bottom covers.
Picture of my newly restored AJ-10 Tuner.
The restoration of my father's Heathkit AJ-10 Tuner was most gratifying. I think my dad would be happy to know that the tuner he built is still in use for background music in my basement workshop. This project 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 radio for enjoyment.
The Eico Model 232 Peak to Peak VTVM (Vacuum Tube Volt Meter) was first introduced in 1954 both as a kit and a complete unit. This meter was revolutionary at the time because it could measure Peak to Peak instead of RMS AC voltage and it's high input impedance, 11 meg DC and 10 meg AC, did not load down the circuit you were measuring. The assembled Eico Model 232 VTVM was used in many vocational electronic programs during it production years. In fact the Model 232 was still being used in my high school T and I (Trade and Industry) Vocational Electronic program in 1986! I found this fine specimen at a rummage sale and look forward to cleaning it up and bringing it back to original specifications.
Step 1 Initial Testing
The first step was to determine if there were any initial issues with the Eico VTVM. I plugged it in and let it warm up for a couple minutes. I put the meter in the DC+ Function and 15Volt Range and was able to successfully measure the voltage of a 9 volt battery. In addition, I put the meter into Ohms function Rx10K Range and was able to successfully measure a 1K resistor. Note, it is important to put the Uni-Probe switch into DC position to measure the battery Voltage and AC/Ohms position for measuring a resistor's resistance. The only issues I notices were that the Zero and Ohms Adjustment Potentiometers were touchy, probably due to being dirty, and that the Rx100K and Rx1M scale did not work.
Step 2 Cabinet Removal
Two screws, circled in red below, hold the cabinet of the Eico Model 232 in place. Once the screws have been removed, place the VTVM face down on a soft cloth then carefully thread the power cord through the center hole while pulling the rear cover up and off.
Look at this ancient D Cell battery installed in the VTVM! When was the last time a D Cell cost 20 cents? The D Cell battery is a current source used when the meter is in the Ohms function setting.
Step 3 Test Vacuum Tubes
Unlike Solid State components, such as Diodes and Transistors, Vacuum Tubes have a finite life and should be checked using a Tube Tester.
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 50 year old electrolytic capacitors!
The Eico Model 232 uses a 10uF 150Volt electrolytic capacitor, labeled C5 in the manual, to filter the DC ripple from the power supply.
I replaced C5 with a modern 22uF 150Volt Radial Capacitor I had in stock.
Step 5 Cleaning and Lubrication
I spray electrical contact cleaner into the open slots of the Zero and Ohms Adjustment potentiometers then rotate the knobs back and forth, full clockwise and then counterclockwise, to clean the wiper connected to the center terminal.
I then use electrical contact cleaner to clean the metal contacts on the Phenolic and Ceramic wafers that make up the Function and Range rotary switches. I spray the metal contacts then work the switch back and forth through each setting.
I use Labelle 107 model train oil to lubricate the shafts of the rotary switches and potentiometers connected to the front panel, then work the oil in by moving them through each position. Labelle 107 oil is great as it will not harm plastics parts like other lubricants.
The Function and Range switch use a ball bearing under tension to produce the ratcheting action needed to lock you into each setting. I use Labelle 106 model train grease to lubricate the race the ball bearing travels on. Labelle 106 Grease will not harm plastic parts.
Q-Tips, moistened with Windex, work great for cleaning hard to reach places on the VTVM chassis. Look how dirty this Q-Tip is after an initial cleaning of the top of the chassis!
Mequiar's PLASTX, meant to clean and polish plastic car parts, also works great on removing the yellowing of a meter face cover! Note, this is a "before" picture of the meter face cover.
Step 6 Rotary Wafer Switch Repair
One of the ceramic wafer decks of the Range switch fell apart during cleaning, I suspect that it already had hairline cracks. This is probably the root cause of why the Rx100K and Rx1M Ohms Range didn't work!
I used Super Glue (Cyanoacrylate) to adhere ceramic parts of the Range switch wafer back together. I then used nylon ties, wrapped around the circumference of the switch wafer, to add permanent strength. I clipped the ends of the nylon ties once the glue dried.
Step 7 Paper/Wax Capacitor Replacement
Paper/Wax capacitors deteriorate with age due to acid in the paper. I decided to replace them with modern Polyester Capacitors.
Here is the original .025 uF 400Volt Paper/Wax Capacitor, designated C3 in the Construction Manual.
Here is the replacement .027uF 630Volt Polyester Capacitor replacement installed.
C2, as designated in the Construction Manual, was also replaced with a .027uF 630Volt Polyester Capacitor.
Here is the original .003 uF 400Volt Paper/Wax Capacitor, designated C4 in the Construction Manual.
Here is the replacement .0033uF 1600Volt Polyester Capacitor replacement installed.
Here is the original .1 uF 1000Volt Paper/Wax Capacitor, designated C1 in the Construction Manual.
Here is the replacement .1uF 1000Volt Polyester Capacitor replacement installed.
Step 8 Cabinet Cleaning
In order to do a thorough cabinet cleaning, you must remove the three chrome button covers, that cover the calibration controls, on the side.
I also remove the leather strap, it is held in place by two by a screw and nut on each side of the cabinet.
A thorough scrubbing in a dishwashing soap bath is in order to remove years of dirt, grime, and tar from tobacco smoke. Rinse then completely dry the cabinet when finished.
Mequiar's Motorcycle All Metal Polish works great for removing rust from the three chrome button covers. Note, this is a "before" picture of the button covers.
I apply two coats of Mequiar's Motorcycle Liquid Wax, buffing it with a chamois between coats, to get the cabinet to shine like when it was new.
Cabinet cleaning is complete, I then reattach the leather strap and installed the chrome button covers.
Step 9 Uni-Probe Repair
The insulator on the ground lead had snapped off.
I used Super Glue (Cyanoacrylate) to adhere it back together. The tie strap holds the assembly together while it dried.
The Uni-Probe was in bad shape. It was held together with electrical tape!
Here is what I found when I removed the electrical tape. The Uni-Probe case was cracked and several pieces of the case fell off. The Uni-Probe contains an internal switch. You rotate the white part of the lead to the DC or AC/Ohms position depending on what is being measured.
I used rubbing alcohol to remove all of the electrical tape adhesive residue from the Uni-Probe. Then, I used Super Glue (Cyanoacrylate) to glue the pieces of the Uni-Probe case back together. A screw with a large head holds the innards of the Uni-Probe in place. This screw is insulated from the probe lead so there is risk of electrical if you touch the screw head while taking High Voltage measurements.
Step 10 Calibration
It is important to re-calibrate the Eico Model VTVM Model 232 after the Electrolytic and Paper/Wax capacitors have been replace. Consult the Eico Model 232 Instruction Manual for the calibration procedure.
Calibration is accomplished by adjusting the AC Balance, DC Calibration, and AC Calibration potentiometers located toward the rear bottom of the chassis.
Performing Calibration on my restored Eico Model 232 VTVM!
With the help of inexpensive replacement capacitors, Super Glue (Cyanoacrylate), some common household cleaning products, motorcycle wax and polish. I was able to make this vintage Eico Model 232 VTVM shine and operate like the day it was built!
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.
Multi-Section Capacitors, which were aluminum cans containing several discrete capacitors all connected to a common ground, were popular in the 1950s and 1960s. 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.
View of the multi-section capacitor, circled in red below, in the AJ-10 Tuner from the top of the chassis.
Pictured below is a multi-section capacitor removed from the chassis. The side of the aluminum can indicates capacitance and working voltage of the internal capacitors.
The guts of a multi-section capacitor, pictured below. I use needle nose pliers to un-crimp the bottom of the aluminum can exposing the innards. I always wear nitrile gloves when working with the guts of capacitors as the remaining electrolyte may cause skin irritation.
I use small brass screws, obtained from a craft store, to hold the terminals of the multi-section capacitor in place. I then solder the new replacement capacitors to the terminals on the capacitor base. The grounds of the capacitors should connect to the outer ground ring. I use a dab of hot glue to secure the capacitors in place. See the results below:
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 for dis-assembly.
Below is how the multi-section capacitor's aluminum can looks like after cutting and smoothing with fine grit sandpaper.
Once the refurbished multi-section capacitors is mounted and soldered back into the circuit, I use hot glue to affix the aluminum can over it.
The refurbished multi-section capacitor looks as good as the original! See below:
My father-in-law Ray, or "The Old Man from California" as he likes to refer to himself, surprised me a couple years ago by offering to give me the majority of his amateur radio equipment. Ray knew I was interested in amateur radio as I have built several regenerative AM vacuum tube receivers recently.
Ray was an avid Amateur Radio enthusiast in the 1970s and 1980s, acquiring many QSL cards, but in recent years he had let his amateur radio license expire and was content with just listening to the amateur radio bands. I think part of the problem was that he was tired of battling with the home owners association and their restrictive CCRs (Covenants, Conditions, and Restrictions) with regard to external antennas. Listening to the amateur radio bands only typically requires a modest internal antenna.
In the next couple months, my father-in-law shipped me the following from his collection:
- Kenwood TS-520 SSB Tranceiver
- Azden PCS-3000 2M FM Transceiver
- Ten-Tec Century 21 CW Transceiver
- Yaesu FRG-7700 All Mode Transceiver
- MFJ 949C Antenna Tuner
The Kenwood TS-520 was the most interesting piece of Amateur Radio equipment to me. It inspired me to study for my amateur radio license.
I worked hard one summer to get my Technician and then my General Amateur Radio License. At the time, I just had a make-shift long wire antenna composed of several test leads connected together terminated to the antenna output jack on the TS-520 by a banana plug. With this simple antenna I was able to pick up transmissions mostly in the mid-west from my northern Ohio location. I was able to determine the origins of the transmissions by looking up the call signs of the senders.
Now I had my General Amateur Radio license and I was ready to tear up the High Frequency Airwaves, make many contacts, and send/receive many QSL cards. With the help of my father-in-law, I strung a G5RV antenna between a big Black Walnut tree and my house then installed a lightning arrestor at the end of the G5RV ladder line. I then looped the transmission line to make the balun and ran the other end to my Radio Shack in the basement. I attached the MFJ 949C antenna tuner between the TS-520 and the transmission line from my G5RV and grounded both the TS-520 and the antenna tuner to the main water line pipe that comes into our house. The main water line is conveniently located under the desk where my amateur equipment is located.
I figured I better transmit into the dummy load built into the antenna tuner first to see the output wattage of my TS-520 so I switched to the 40 Meter Band, changed the mode switch to CW and keyed the microphone. How disappointing, the cross-hair meter on the antenna tuner only indicated 10 Watts P to P. The TS-520 manual indicates it should output 160 Watts P to P!
Okay, so I read the manual and discovered the page on Transmitter Tuning, I am from the "point and click" generation an it never dawned on my that I would have to tune the transmitter circuit for resonance. I figured the rig would take care of it. I went ahead and followed the Transmitter Tuning procedure then I keyed the microphone again and now the transmitter power output was 50 Watts P to P through the dummy load. This was an improvement but still far short of the 160 Watt specification. Time to crack open this vintage TS-520 and see what has gone awry!
Unplug the TS-520 from the power source before opening the cabinet. This rig can generate potentially life threatening voltages of over 800 Volts DC that is used to power the vacuum tubes in the final transmitter power output section of the transmitter.
Step 1 Top Cover Removal
Remove the four top screws circled in red.
Remove the two screws circled in red on the side with the handle.
Remove the two screws circled on red on the side with the feet.
Remove the connector from the internal speaker.
I use disposable salad bowls to hold all of the screws I remove during dis-assembly.
Step 2 Bottom Cover Removal
Pull the plastic clips circled in red then remove the side cover.
Underneath the side cover is the Side Panel Controls.
Remove the two screws circled in red on the side with the handle.
Remove all screws circled in red from the bottom, you should now be able to pull the chassis free from the bottom cover.
Step 3 Cathode Resistor Visual Inspection
Inspect the Cathode resistors (circled in red), installed on the bottom side of the Final Power Amplifier Board, for overheating and charring. Typically these are 10 ohm 1 Watt resistors. A previous owner replaced these with two 20 ohm resistors.
Step 4 Cathode Resistor Resistance Check
All cathode resistors are in parallel and connect to ground. Resistance from the top of any Cathode resistor to ground should be 5 ohms. If over 5 ohms replace.
Step 5 Cathode Resistor Replacement
Cathode resistors must be replaced if charred or the total resistance of all cathode resistors is over 5 ohms. I replaced with two 10 ohm 1 Watt Flame Proof Resistors.
Cathode Resistor Replacement Warning!
Each Cathode resistor should be replaced with a 10 ohm 1 Watt resistor. Kenwood uses these resistors as fuses to protect the finals and power transformer if the rig is mistuned for any length of time. Replacing these resistors with larger wattage ones could allow more expensive parts to be damaged!
Do not replace the Cathode resistors with wire-wound types. This could introduce unwanted reactance into the transmitter circuit.
Step 6 Testing after Cathode Resistor Replacement
Once the Cathode resistors were replaced, it was time to bench test the TS-520 by transmitting into a Dummy Load to see if this resolved the problem. Be careful when powering up the rig with its cover removed. Do not touch any of the exposed circuitry in the chassis while it is plugged in.
In order to do an apples to apples comparison, I once again set the TS-520 to the 40M band then performed the Transmitter Tuning procedure in the manual. I then set the mode switch to CW and keyed the microphone button while watching the cross needles on my MFJ 949C set in the Dummy Load position. The power output was an improvement, it increased from 40 Watts P to P to 70 Watts P to P. This was a great improvement and I was excited but it still was not up the 160 Watts P to P specified in the manual.
Time to remove power from the rig and continue to troubleshoot issues in the transmitter power amplifier area!
Step 7 Final Power Amplifier Cover Removal
Remove the three screws, circled in red, from the side of the Final Power Amplifier Cover.
Remove the three screws, circled in red, from the top of the Final Power Amplifier Cover. Pull cover straight up and out.
Step 8 Discharge Final Power Amplifier Capacitors
Before proceeding, touch a test lead between the metal chassis and the metal top of the coil that sits between 6146B vacuum tubes to discharge any remaining high voltage!
Step 9 Vacuum Tube Testing
Remove the Anode cap then carefully pull the vacuum tubes, circled in red, up an out of thier sockets.
Remove the driver vacuum tube, circled in red.
Use a suitable tester to test each tube. Replace if tube is defective or shorted. 6146B tubes do not have to be replaced in matching pairs. If you replace a 6146B tube, you will have to following the "Transmitter Neutralization" section in the manual.
Step 10 Testing After Vacuum Tube Replacement
If you have to replace the driver or final tubes you should retest by transmitting into a dummy load to see if this resolved the problem. Be careful when powering up the rig with its cover removed. Do not touch any of the exposed circuitry in the chassis while it is plugged in.
When retesting, do an apples to apples comparison. First perform the Transmitter Tuning procedure in the manual, then set the Mode switch to CW and the Band switch to 40M. Key the microphone key and measure the transmitters output wattage.
All of the vacuum tubes tested normal in my TS-520 so I am going to remove power from rig and proceed to step 11.
Step 11 Final Power Amplifier LC replacement
Many TS-520 repair sites recommend replacing the components circled in red even if they test good. C1 .001 mfd 3KV, C2 .0047mfd 1.4KV, L1 5uH 500ma RF Choke. This is my next troubleshooting step as these parts are relatively cheap.
I recommend removing the rear cooling fan for easier access to the C1, C2 and L1.
Comparison of the original components to the new ones. The blue capacitors and the small encapsulated inductor are the new components.
Picture of new LC components soldered in place. I had to use three capacitors in parallel to achieve the same capacitance and working voltage rating for C1.
Step 11 Testing after Final Power Amplifier LC replacement
Once the capacitors and inductors were replaced in the Final Power Amplifier, it was time to bench test the TS-520 by transmitting into a dummy load to see if this resolved the problem. Be careful when powering up the rig with its cover removed. Do not touch any of the exposed circuitry in the chassis while it is plugged in.
In order to do an apples to apples comparison, I once again set the TS-520 to the 40M band then performed the Transmitter Tuning procedure in the manual. I then set the Mode switch to CW and keyed the microphone button while watching the cross needles on my MFJ 949C set to the dummy load position.
The power output increased from 70 Watts P to P to 160 Watts P to P which was specified in the manual. A combination of replacing the Cathode resistors then replacing capacitors and an inductor in the final transmitter amplifier resolved the problem.
Only one problem, when I changed frequency bands the power output decreased again. Upon re-reading the manual it dawned on me that I have to perform the Transmitter Tuning procedure each time I change frequency bands in order to bring the Final Power Amplifier into resonance. 160 Watts P to P was achieved on all frequency bands each time after the Transmitter Tuning procedure was performed from the manual.
My TS-520 rig at Full Power Output!
My Radio Shack ready for some serious CQ DX!
The recently repaired TS-520 is the centerpiece of the Radio Shack.
As you can see, I was able to diagnose and repair the low transmitter power output problem of my Kenwood TS-520, at the minimal cost of a handful of passive electronic components, and a few weekday evenings.
I hope this hub encourages you to revisit a TS-520 that you have sitting on a shelf or in a closet collecting dust, due to a low transmitter power output problem, and bring it back to life!
Useful Kenwood TS-520 Links!
Great resource for repairing Kenwood Hybrids such as the TS-520. Also a great source for hard to find TS-520 parts!
Kenwood Hybrid Restoration & Repair, Models TS830S, TS530S, TS820, TS820S, TS520, TS520S, TS520D, TS520SE, TS520SP
Downloadable manuals and info for Kenwood TS-520S, Manuals for DG-5, Manuals for AT-200, AT-230 Manuals for VFO-520S
Getting Started in Electronics by Forrest Mims III is a great book for anyone interested in electronics!
This book has had a major affect on my life and the career choices I have made. As a kid growing up in the 1980s, I used to regularly frequent our local Radio Shack store. I used to love looking at their electronic parts collection wondering what I could make out of them. At the time I was 12 years old and was too young to enroll in any electronic classes at school. I was also part of the Radio Shack “Battery Club” where I would get one free battery each month. Remember those days? I wanted to get to know more about electronic so the store manager recommended I pick up a copy of Getting Started in Electronics book which was one of many publications by Forrest Mims that Radio Shack stores carried at the time.
This book is awesome, it covers basic electricity and electronic theory in a very easy to read fashion with cute hand drawings. Later on in the book it covers discrete electronic components, their schematic symbols, and their electrical properties.The book starts with pictorial drawing of circuits then moves on to schematic diagrams.As an added bonus, the back of the book contains one hundred circuit projects that you can build on your own!
This book has changed very little since I purchased my copy in the early 1980s, but the theory and electronic circuits found in this book are still sound! It can be found at online retailers such as Amazon.
This book inspired me to take vocational electronics in high school where we learned about vacuum tubes, transistors, and TTL (Transistor Transistor Logic). I ran a successful TV/VCR repair business out of my parents basement and used the money to pursue my electronics hobby and to pay for car expenses. Later on I pursued a Bachelors Degree in Electronic Engineering Technology and worked on everything from electronic weigh systems used in steel mills to CNC Lathes used in the shipbuilding industry. I used electronics as a stepping stone into my current career as a Systems Administrator in the computer field.
I recommend this book for kids and adults alike that want to know more about electronics!
My original copy of Getting Started in Electronics from the 1980s!
The year was 1983, and I had just finished reading "Getting Started in Electronics" by author Forrest M Mims III, which was a publication distributed through Radio Shack stores. I was ready to get my hands dirty in building the 100 electronic projects at the end of this book and I needed a basic Volt-Ohm-Meter to troubleshoot the circuits I built on my trusty breadboard.
At the time I didn't have a lot of money as my only employment at age 13 was a paper route.
Radio Shack offered two choices in my price range. The already assembled Micronta 1000 Ohm/Volt Multimeter or the kit form ArcherKit Multimeter Model 28-4012A. Operation wise, both multimeters were identical but just had some cosmetic differences. The Micronta had a black case with "Micronta" silk screened on the meter face while the ArcherKit had a light blue case with the meter face emblazoned with "ArcherKit".
Being cost conscious, I chose the ArcherKit Multimeter Kit because it was several dollars cheaper than the Micronta and, besides, I needed to work on my soldering skills!
Assembly of the ArcherKit Multimeter Kit was fairly straight forward. You had to solder all of the required electronic components in place and install wire jumpers over to the built in battery holder. The only difficult part I remember was using the solder iron to melt plastic posts used to secure metal contacts, where the test leads are to be connected, to the back side of the multimeter face. Too much heat and you could melt through the front cover of the multimeter face from the back side!
The ArcherKit Multimeter Model 28-4012A was just what I needed. While it could be laborious to keep inserting test leads into different meter face sockets to change between Voltage Ranges, AC, DC, and Ohms settings, most of my troubleshooting was done in the 15Volt Range in DC measurement mode so this was not an issue.
I imagine many people at one time owned the ArcherKit Multimeter Model 28-4012A when getting started in Electronics. It had served me well for many years until I graduated to a fancy auto-ranging Digital LCD Multimeter. Even now my ArcherKit Multimeter has its place in my toolkit for when I need to take some very basic voltage measurements.
HP-23A Power Supply Background
This HP-23A Power Supply was designed by Heathkit back in the 1960s to provide the necessary supply voltages for fixed station AC operation of Heathkit SB and HW series HF amateur transceivers. This HP-23B and HP-23C are variants of the HP-23A power supply and are similar except they have the following additional features:
- An internal circuit breaker instead of the fuses built into the AC plug.
- Switch selectable low voltages of 350 or 275 VDC.
- The ability to be wired for 240VAC or 120VAC, 50-60 Hz input voltage.
- Fixed instead of adjustable -130VDC Bias Supply.
HP-23A Power Supply Specfications
The HP-23A Power Supply accepts an AC input voltage of 120 VAC 50-60 Hz.
It provides the following outputs:
Filament = Isolated 6 and 12 VAC, 5.5 Amp power supply.
High Voltage = +820 VDC, 250ma output generated by a full-wave voltage doubler.
Low Voltage = Internal jumper selectable, +350VDC or +275VDC, 100ma output generated by a half-wave voltage double.
Fixed Bias Voltage = -130VDC, 20ma generated by a half-wave rectifier.
Adjustable Bias Voltage = Adjustable, via Bias Control, up to -130VDC.
External Switching = Power to HP-23A can be controlled by an external Heathkit SB and HW series HF amateur transceivers or other Heathkit ham radio equipment.
Single Connection = All output power is transferred to external Heathkit SB and HW series HF amateur transceivers via a multiwire "Umbilical Cord" with 11 pin connectors at each end.
Step 1 Bottom Cover Removal
Four screws hold the bottom cover of the HP-23A Power Supply in place. See areas circled in the picture below:
Below is a picture of the inside of the HP-23A Power Supply.
The HP-23A incorporates two glass cartridge fuses in the AC plug. See picture below:
Step 2 Initial Testing
The next step is to perform initial testing in order to determine any issues. You will need to jumper pins 9 and 10 on the output socket in order to energize the power supply. I have done so with a yellow alligator test lead. I use my Volt-Ohm-Meter to measure and record each no-load output voltage. I will compare these voltages with the voltages measured after the restoration has been completed. Be careful as you can contact potentially life threatening voltages with the bottom cover removed!
Step 3 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 HP-23A Power Supply!
The High Voltage output section uses a full-wave voltage doubler while the Low Voltage output section uses a half-wave voltage doubler. These power supplies employ four 125uF 450Volt Electrolytic Capacitors circled below:
Make a note of where the Phenolic and metal capacitor mounting wafers are placed. See areas circled in the picture below. It is important that they are installed in the same location otherwise the High Voltage and Low Voltage sections of the power supply will not work correctly!
Pictured below are the 125uF 450Volt capacitors from the High Voltage and Low Voltage section removed from the HP-23A chassis. We will need to salvage the Phenolic and metal capacitor mounting wafers to install on the replacement capacitors.
With the capacitors removes, it is now a good time to clean the top of the HP-23A chassis. I use Q-tips moistened with Windex to get into hard to reach spots. See picture below:
It is easier to replace the Low Voltage and Fixed Bias capacitors, labeled C5, C6, and C7, in the schematic, with the external 125uF 450Volt electrolytic capacitors removed. That will be the next course of action.
You will need to remove the Bias Control potentiometer and the terminal strip next to it in order to replace the internal chassis capacitors used that are part of the Low Voltage and Fixed Bias power supply. See area circled in the picture below:
I replaced the 40uF 450Volt (C5) and the two 20uF 150Volt (C6, C7) electrolytic capacitors with modern 47uF 450Volt and 22uF 150Volt electrolytic capacitors, but did not mount them back into the chassis until the external 125uF 450Volt electrolytic capacitors were replaced. See picture below:
I replaced the 125uF 450Volt electrolytic capacitors (C1, C2, C3, and C4 in the schematic) with Cornell-Dubilier 150uF 450Volt (Manufacturer Part No: 381LX151M450K022) electrolytic capacitors. These Cornell-Dubilier capacitors are typically used in switching power supplies. These capacitors are much smaller than the originals. See picture below:
Below is how I prepared the metal capacitor mounting wafers to accept the new Cornell-Dubilier 150uF 450Volt electrolytic capacitors. I soldered a lug to the mounting wafer that will connect to the negative terminal for the capacitor. See below picture:
Below is a picture of the new Cornell-Dubilier 150uF 450Volt electrolytic capacitors installed on their capacitor mounting wafers. Several dabs of hot glue keep them in place on the wafers.
Two of the replacement 150uF 450Volt capacitors, labeled C1 and C2 in the schematic, require parallel 100K 2Watt Resistors across their leads. In addition, C1 needs a jumper wire over to the rectifier diodes located on the terminal strip. It is easier to solder these in place before install the capacitors in the chassis. Please see picture below:
Time to mount C1 and C2 back into the chassis and wire in place, pictured below:
And now mount C3 and C4, circled in red below, then wire in place, as pictured below:
At this point the adjustable Bias Control potentiometer and the terminal strip that connects electrolytic capacitors C5, C6, and C7 is still not mounted into the HP-23A chassis. It is easier to wire the AC cord with these components not mounted to the chassis.
Step 4 AC Cord Wiring
I will be replacing the original two conductor AC cord, and non-polarized plug, with a three conductor AC cord and polarized plug that includes a ground pin. The original non-polarized plug had two 4 Amp fuses contained in the housing, see picture below:
I relocated the fuse holder inside the chassis, only one 4 Amp fuse is required, connected to the "Hot" side of the AC cord. See area circled in the picture below:
Time to finish up the wiring! I use two zip ties to act as a strain relief in order to prevent the AC cord from being pulled out of the chassis. The green wire from the AC cord connects directly to the chassis by solder lug. The black wire from the AC cord connects to one terminal of the fuse holder and a jumper wire connects to the other terminal of the fuse holder to the power switch. The AC cord white wire connects to the end terminal strip where the black wire of the transformer is terminated.
Finally, we can mount the Bias Control potentiometer and the terminal strip with C5, C6, and C7 back into the chassis. One lead of C5, C6, and C7 connect to the chassis by solder lug. See areas circled in the picture below:
Step 5 Final Testing
The next step is to perform final testing in order to determine any issues. You will need to jumper pins 9 and 10 on the output socket in order to energize the power supply. I have done so with a yellow alligator test lead. I use my Volt-Ohm-Meter to measure and record each no-load voltage, I will compare these voltages with the voltages measured before the restoration has been completed. You will notice that the High Voltage, Low Voltage, and Fixed Bias Voltage will be slightly higher than before the restoration, this is because the new capacitors are doing a better job of filtering the pulsating DC voltage from the rectifiers. Be careful as you can contact potentially life threatening voltages with the bottom cover removed!
Step 6 Detailing
Once the bottom cover is in place, I like to treat the chassis to a coat of wax so that it shines like the day it was built. I use Meguiar's Motorcycle Liquid Wax as I have it around for use on my motorcycles. Actually, any liquid car or motorcycle wax will do. First I unplug the HP-23A power supply, then I carefully apply two coats to the chassis, top cover (if equipped), external capacitors and transformer shells, carefully wiping all components with chamois in between each coat to remove any white residue. This really brings out the luster in the paint, see pictures below:
Step 7 Final step of putting the HP-23A Power Supply back into production!
My newly restored HP-23A is ready to be put back into production once the top mesh cover is installed. I use my HP-23A to power a vintage Heathkit HW-101 SSB Transceiver. See picture below:
Knowing my new interest in Amateur Radio, my father-in-law, or the "Old Man from California" as he likes to call himself, offered me his old ham radio equipment that he no longer used. I readily agreed. In the next couple months, my father-in-law shipped me the following from his collection:
- Kenwood TS-520 SSB Tranceiver
- Azden PCS-3000 2M FM Transceiver
- Ten-Tec Century 21 CW Transceiver
- Yaesu FRG-7700 All Mode Transceiver
- MFJ 949C Antenna Tuner
This encouraged me to obtain my Amateur Radio Technician license. As soon as I passed I immediately started fiddling with the Azden PCS-3000 2M Transceiver. I installed a J-Pole antenna, made by Arrow Antenna, in the attic and routed the coax transmission line through the closet on the first floor and to my Radio Shack in the basement. I knew that the J-Pole antenna was closely impedance matched to the RF output of the Azden PCS-3000 so that no Antenna Tuner was required. I set the frequency offset and enabled the PL Tone switch on the top of the transceiver and was ready to make contacts!
Despite repeated attempts I was unable to trigger the local repeater. I then decided to put my MFJ 949C Antenna Tuner in series with the PCS-3000 and the J-Pole antenna. I set the Antenna Tuner to direct mode bypassing the internal LC circuit. The issue became evident. Keying the microphone produced no RF output to the antenna! The cross needle meter on the Antenna Tuner did not indicated any forward or reflected power. Time to take apart to the PCS-3000 to determine the issue!
Disassembly - Loosen Control Unit Knobs
Time to figure out what's "broke", first you must remove the detachable control unit. This is done by loosening the knobs on each side of the radio.
Disassembly Tip - Organization is important!
When disassembling a radio, I carefully place the parts into two bins, one bin for the larger parts and a smaller bin for the screws.
Disassembly - Remove the control unit
Pull the control unit strait forward, the control unit attaches electrically to the body of the radio by an edge connector.
Dissaembly - Remove the mounting rails
There are two mounting rails, one on each side of the radio. Two counter sunk Philips screws hold them in place. Remove the screws then pull the rails off.
Disassembly - Top cover Removal
The bottom cover is held in place with four screws, one at each corner of the cover. Remove the four screws and pull the cover off. The speaker is attached to the bottom cover, you will need to disconnect the speaker from the printer circuit board.
The RF Amplifier Module
The Taiyo VP-15E13LF RF Module is circled in red, I believe that this is the failed component but need to do some checks first.
Voltage and Signal Checks
All voltage and signal measurements are taken with reference to the metal chassis. I attached the negative lead of my Multimeter and ground lead of my Oscilloscope to the internal metal chassis when making measurements. Signal measurement is in Volts Peak to Peak.
PA Board Input Checks
Measurements taken on connector circled in red. PIN5 12 Volts DC, PIN9 9 Volts DC, PIN4 9 Volts DC when MIC keyed. PIN1 9 Volts DC when MIC NOT keyed.
PA Board Input Checks (Continued)
You should see a small FM signal (under 1 Volt) on the IN pin circled in red when the MIC is keyed.
RF Amplifier Module Checks
IN, VC, VD, OUT are marked on the PA printed circuit board. IN should be a small FM (under 1 Volt) signal when MIC is keyed. VD should be around 9 Volts DC, VC should be 12 Volts DC. OUT should be an FM signal of several volts when MIC is keyed.
My Troubleshooting Results
I have determined that all the proper voltages and signals were present going into the PA Circuit Board. I have also determined that the proper voltages where present on the pins of the Taiyo VP-15E13LF RF Amplifier and the proper FM signal was present on the IN pin of the RF Amplifier Module but that no signal was present on the OUT pin of the RF Amplifier Module. This leads me to believe that the RF Amplifier Module is defective.
The RF Module is made of Unobtainium
The Taiyo VP-15E13LF RF Amplifier Module part has been discontinued. I like to say is that it is now made of "Un-obtainium". I cracked the RF Module open to see if there was any serviceable parts. The RF transistors that are in the Taiyo VP-15E13LF RF Amplifier Module are available but our expensive as they have been discontinued as well. The RF transistors were too expensive to justify the repair of this aged 2M Transceiver that is worth under $100 in working conditions. Time to look for alternatives.
Inside the Taiyo RF Amplifier Module
What's inside the Taiyo VP-15E13LF RF Amplifier Module
The M57737 RF Amplifier Module
Pinout and package dimentions of the Mitsubishi M57737 RF Amplifier Module
Source for replacement Mitsubishi M57737 RF Amplifier Module
As mentioned, the pin layout of the the M57737 is slightly different. The M57737 does not have any ground pins but instead the metal base of the module is ground.
Make sure you apply heat sink compound to the back of the RF Amplifier Module before mounting.
Here are the connections of the M57737 to the PA Board:
M57737 Pin | PA Board Connection
Pin1 ============ IN
Pin2 ============ VD
PIN3 ============ VC
PIN4 ============ Anode of D30 which is connected directly to OUT
Metal Case ======= Any connection designated as G
The Transplanted M57737 RF Amplifier Module
The M57737 mounted and soldered in place. Notice the ground connection between the M57737 metal case and G on the PA printed circuit board.
A Leap of Faith
I had no idea if the replacement Mitsubishi M57737 RF Module was going to work. It was a $50 gamble! That was the cost of the replacement part. I could easily power it on an smoke the new RF Amplifier module.
I moved the Azden PCS-3000, with the newly installed RF Amplifier module, over to the desk in my Radio Shack, connected power and attached the antenna output to my MFC 949C Antenna Tuner. I then set the Antenna Tuner to use the built in dummy load.
Upon power up there was no smoke....whew....the PCS-3000 was working correctly in receive mode. I checked voltages at VC and VD points on the PA printed circuit board, they look correct.
Time to key up the MIC and transmit into the Dummy Load. Success! I was reading about 100 Watts Peak to Peak as forward Wattage on the cross-hair meter on my Antenna Tuner.
Once connected to my J-Pole antenna, I was able to trigger our local repeater and establish contact with a fellow Ham on the 2 Meter band.
Bench testing my Azden PCS-3000 after the RF Amplifier module implant.
The Down Side
As part of my testing, I decided to try low power mode which is accomplished by pulling the Squelch control out. Low power mode effectively cuts the RF output power in half. I heard a "pop" as soon as I keyed the MIC in low power mode. It blew the inline fuse in the power cable. I immediately turned off my 12 Volt bench power supply. My first concern was, did it blow the newly installed RF Power Amplifier module? I replaced the inline fuse with a suitable size, pushed the Squelch control back in, putting the PCS-3000 back into high power mode, and turned the 12 Volt bench power supply back on. The PCS-3000 sprang back to life and when I keyed the MIC I was still able to contact our local repeater.....whew.
My solution to this problem was to not use the low power mode and to place a sticker on the top of the rig warning to not use this function.
Back in Service
My Azden PCS-3000 back in service in my Radio Shack!
My transplant of a similar Mitsubishi RF Amplifier module into my vintage Azden PCS-3000 2M Transceiver was a success! I am hoping that this Hub will help you in diagnosing and fixing a "no RF output" problem with your PCS-3000 was well.
In the early days of electronics, vacuum tube devices were powered by batteries as many homes had not been wired for electricity. The batteries used for powering these early electronic vacuum tube devices were classified as "A", "B", and "C" batteries.
The "A" battery was used to provide power to the filament of a vacuum tubes in the device. Typically this battery was low voltage (usually between 2 to 7.5 volts) but required a high amperage to power the vacuum tube filaments. Lead-acid types, like classic car batteries, were used initially until better high amp-hour Zinc-Carbon batteries were developed.
The "B" battery was used to provide the plate voltage of a vacuum tube. These were typically of Zinc-Carbon variety with many cells wired in series to provide the low amperage and high voltage (usually 22.5, 45 or 90 Volts) required.
The "C" battery was used to provide bias to the control grid of a vacuum tubes. This was typically a low voltage and low amperage (9 Volts with several 1.5 Volt taps) Zinc-Carbon battery. The C battery was largely done away with as it was soon discovered that the needed voltage/current bias could be derived from the "A" battery using a grid leak resistor or voltage divider biasing.
Pictured about are examples of an "A" and "B" battery I just pulled out of a 1947 TRAV-LER Model 5020 portable vacuum tube radio that I am in the process of restoring. Two "A" batteries were connected in series to provide the required 9 Volts for the tube filaments. In addition, two "B" batteries are connected in series to provide the required 90 Volt plate voltage. No "C" battery is required as the Model 5020 uses grid leak resistors to provide required voltage.
I plan on gutting these vintage "A" and "B" batteries, then installing modern batteries wired in the proper fashion to achieve the proper voltage/current required.
The writing was on the wall that vacuum tubes were becoming obsolete while solid state components, such as transistors and diodes, were taking place of many vacuum tube applications.
In 1961, for one last fanfare, General Electric introduced the Compactron, a vacuum tube family to compete with solid state diodes and transistors. The idea with the Compactron was to integrate several vacuum tube components (Diodes, Triodes and Pentodes, oh my!) into a single glass envelope with all components sharing the same filament, thereby, lowering power consumption and the amount of heat generated. Two identifying characteristics of a Compactrons are a 12-pin footprint and evacuation glass tip located at the center bottom instead of the top of the vacuum tube.
While the Compactron never fully stopped the onslaught of the transition to solid state diodes and transistors in the electronic industry, it did carve out a niche market being used in many low cost hybrid (using both solid state and vacuum tube components) portable color televisions of the 1960s until mid-1970s. The Compactron was used in high voltage, or high current circuits applications where early solid state diodes and transistors were not suitable.
Eventually solid state diodes and transistors technology became more mature and new lines of these solid state components were designed for high voltage/current applications taking the place of Compactrons. Compactrons were completely phased out of new electronics by 1986 but had a good run of 25 years!
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
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