Refurbishing a Heathkit HW-101



My first transceiver back in 1982 was a Heathkit HW-101. It was not a high quality radio, but it was good enough for most operators. The filters were wide as barn doors, there was no RIT nor XIT, and for a serious DXer the lack of a second VFO was a bummer. On the other hand, it's basic construction was ok, it's documentation was excellent, and it was easy to modify it and to add the lacking functionalities oneself, and there was a built-in place for a CW filter. And most importantly, as the radio was sold as a kit it was affordable. It is no wonder that it was a very popular radio during 1970's. I was a school boy having only little money and I paid something close to 1800 markkas for a used HW-101. According to Band of Finland that is about 720 euros in 2015 money. That was about all the money I had.

As far as I remember, my Heathkit had only one modification. The antenna connector had been changed to UHF type. The first modification I did was to change the original microphone connector that was difficult to get to something more common. And then to the bands. CW filter was needed, so I added one. That was easy. No RIT nor XIT, right, so trying to get DX in pileups was difficult. That's why I added RIT and XIT. Well, it was ok for some time, but clearly it was not as good as a second VFO. So I added one. The dial was not quite accurate, so I built a digital frequency counter. At some point of time I bought an audio speech processor, too. So far so good, all my modifications were useful. And then I painted the dial to red so that it woud look cooler. That was a mistake, it looked awful.

I was young and enthusiastic DXer and I needed a better radio. I bought one and to finance it I sold my Heathkit. One day I also sold a box full of spare tubes which I regret still today. Well, perhaps I needed the money for some other radio related stuff.

The years passed quickly and I got more weight and more DX. Sometime in late 2016 I saw an add, that there would be an auction at the Helsinki Radio Club OH2AA. Among loads of other stuff there was a lone Heathkit HW-101 for sale. I went to the auction and came out of it with the radio and it's home made power supply. Did I remember to say that to save money these gadgets were sold as kits, and to save even more money many radio owners did not buy the original Heathkit power supply but they built one themselves.

My bid had been almost ridiculously low, so rightfully I could not expect much. In fact, when going to the auction I only wanted something that would remind me of my past. Something I could store on a bookshelf to see. I did not expect it to work. Opening the lid back home revealed that the radio was dirty, but basically everything seemed to be there. The only striking observation was that the drive belts had been replaced with rather strange looking ropes. As they turned the capacitors just fine, I would later leave them as they were. VFO knob turned smoothly which was a good sign so that perhaps the radio might be in a reasonable condition otherwise, too. My appetite grew, and I changed my plans to making the radio functional again.

A superficial inspection revealed the power supply having so many defects, that to build a new power supply was clearly a priority before anything else could be done. The schematic diagram of the new power supply is below.



The only old power supply parts that I reused were the power cable and the power connector to the radio. I resoldered all the leads and protected the outside of the connector using heat shrink tubing. I did consider if I should change the power connectors to better MIL connectors. Technically that would have been better, no doubt, but I did not want to change the appearence of the radio unnecessarily. Anode voltage for the finals is a bit low 650V due to the transformer I had in hand so somewhat reduced output power was to be expected.


The first thing to do with the radio was to clean the boards using a vacuum cleaner and a paint brush. I changed C2, C12, C212, and C304 of the electrolytic capacitors. I did not change C906 as it apparently had been changed before. I cleaned the switches, tube sockets, and potentiometers using CRC and by rubbing the switch wafers that I could access without disassembly. Later I found that I had done this part poorly.

I measured all resistors. A few seemed to be completely out of specs, but analysis of the schematic diagram revealed that it was not really so. The measured values seemed odd only due to interactions with other resistors. In fact only one of the power resistors of the audio board actually had some 20% lower value than the original one. I did not change that one, as I thought that it would not affect the functionality of the receiver too much. Later that was proven to be the case.

The meter panel light bulbs should be 6,3V 150mA and they should have bayonette connectors. The light bulbs were 300mA models and one of them had an Edison connector. This would unbalance tube filaments and might cause unexpected failures, so I installed new light bulbs having correct ratings. A fellow at the club had offered to test the tubes with his tube tester. Due to travel reasons this was not to happen, so I set myself to buy some spare tubes. This became quite costly an affair. A few tubes I got for free. The rest I ordered from different places, and that's why postage costs became excessively high. I should have kept the tubes I had in early eighties.

I had decided that I would repair my new antique radio, but what does that really mean? There are different schools on thought about this. If you want a real restoration then you must not change the appearance and functionality of the radio at all. For example, if you change electrolytic capacitors to modern ones you should hide the new ones inside of the shells of the original ones. Only changes allowed are the ones you absolutely must do for safety reasons. I was not willing to go this far, though I did keep the shells of the original electrolytic capacitors in storage. Just in case I'd change my mind some day. And definetely, for heavens sake, you must not do any modifications to your radio. As my radio was practically unmodified, I kind of wanted to keep it that way. So I stumbled to the very same problem I had had with my earlier Heathkit, i.e. the 80-MC2M microphone plug is hard to get and it costs a fortune. I was not going to pay more than 30 euros for some microphone connector (including postage and taxes). I was going to build one myself. It turned out to be a fairly simple affair. I just soldered small pieces of 2,0 mm brass rod to an ordinary three pin microphone connector, and that was it.


OK, I had an old SSB transceiver but I did not have a proper microphone for it. I did have a bunch of electret microphones, but using them in a vintage radio somehow felt a bit wrong. I needed a vintage dynamic microphone. Luckily, a colleague was selling loads of old stuff, and among the items to sell were two vocal microphones built by AKG in seventies. Unfortunately their impedance was way too low for my radio. That's why I had to build a microphone amplifier. The schematic diagram is shown below.


Well, then came the moment of truth. Time to switch on the radio. I had bought a variac just for this purpose. The first test was with only the final tubes installed. I increased the voltage slowly, very slowly. Nothing happened. No bangs. No smoke. Just some glow of the tubes. OK. Looks promising. At least there were no shortcuts.

Then I added the other tubes and again slowly switched on the power. To my surprise not much happened, except that there was noise in the loudspeaker. Good. Let's try if the calibrator works. It did. Hey, the receiver works. Let's try it with an antenna. I heard signals. I begun to believe that I really will repair this radio.

It was time to test the transmitter. I got about 10 watts out on 15 meters on tune position. I also tested a few other bands and I got roughly the same result. Good. However, the mode switch felt unreliable. Sometimes I got some power out and sometimes I did not. Sending CW worked on PTT control, when it happened to work, but VOX did not work at all. I tried changing V12, V15, and V17 tubes. A new V17 improved the situation just a little bit, i.e. transmit relays made small movements that were not enough to switch the transmitter side on. Measuring voltages over D201 diode showed 13,3V when keying the transmitter and 2mV when not keying. The problem had to be somewhere after the beat tone oscillator. At the connection of D202 diode and R219 resistor I saw 14,8V when not keying and 0V when keying. The voltages were the same when using PTT which worked ok, so apparently the relay amplifier was ok but still the transmitter was not keying properly.

This was getting weird. The mute functionality of the radio did not seem to be working properly, and recovery was slow. Removing the anti-trip circuit from the equation by unsoldering a wire did not change anything. The lead to the solution came by coincidence. When I touched the microphone pin on USB suddenly VOX worked. So the problem manifested itself only on CW. A few other attempts later I saw different output powers, and CW sidetone became chirpy. This had to be some mechanical disconnection. When I cleaned all relay contacts using small paper strips and cleaning spray, VOX begun to work both on SSB and on CW. That was it. VOX was still quite slow, though. The all knowing internet suggested that R328 resistor should be changed to a smaller one. I changed the original 470k resistor to 100k, and VOX became fast. Good, one problem was finally solved.

But then output power was far too low, it was only 5W. How come, it had been 10W earlier. I changed the driver tube V7 of 6CL6 type. No change of output power. Besides, when I listened my transmission using another radio it was apparent that CW was really chirpy. Where did I still have contact problems? Occasionally switching mode changed output power, so apparently I had not cleaned all mode switch wafers properly. Well, that was no wonder, as to clean all the surfaces one has to detach the switch and the front panel. But then came the final solution. I noticed that rotating carrier null potentiometer caused massive rasping sound to the transmission. I had forgotten to clean that one. So, some more cleaning I did. First I sprayed some CRC to the carrier null potentiometer, and then I removed the mode switch and cleaned all the wafers using a small screwdriver and cleaning spray, not only those wafers that are easy to reach.

I assembled all things back to where they were supposed to be, and voila, rotating the carrier null potentiometer did not cause any unneeded noises to the transmission. Besides, minimizing carrier leakage by rotating the carrier capacitor and the carrier null potentiometer increased output power to 40 watts. Hip hurrah. I declared the project a success regardless of other developments or any lack of those. I tried to change some other tubes in search of the reason for only 40 watts rather than 70 or 80 watts that I thought I should get, considering my somewhat low anode voltage. The only thing found with these experiments was that a 6AU6 spare tube built by National is bad. The radio gave the very same output power when this tube was in V3 position, but there was a strong 50 Hz hum using this particular tube. Go figure. I changed V3 back to the original one, and the hum disappeared. I also replaced R202 with a wire to increase drive, but this did not improve anything. The plate current was about 150 mA, so I would assume somewhat more power. I then retuned coil T1 according to the instructions, as the coil slug was very close to CCW position instead of 14 turns CW direction as instructed. Checking through all the bands i got about 70W on 80, on higher bands I got less, at the edge on 10 I got only 5W. Apparently the final tubes were not too good any more. A new set of final tubes produced 80W on all bands except something like 35W on 10. I have one more set of 6146A tubes but as this radio is now good enough for demonstrations I let it be the way it is for the time being.


Just to note that when the radio showed signs of working, I somehow lost control of the project. If I have any type of a vintage microphone shouldn't I also have an original vintage microphone connector, even if that might be overpriced. Yeah, I did buy one after all. Remember that I had built a plug myself? But it's orginal now, you see. Having soldered a used Amphenol 80-MC2M microphone plug I can conclude with confidence that it has been a great fortune to the humankind that this particular connector type has never become popular. The very same time I also ordered a CW filter. And then I really, really wanted to get a good looking microphone. That's how Astatic 10-D with G stand came to the family. Yes, it was expensive. But it just looks so gorgeous. The final touches were to make 4mm diameter threads for European screws to the bottom panel as I didn't have any American size screws, to buy some 3mm stainless steel screws for the back panel, to clean the exteriors using computer screen cleaning liquid, and to make a test QSO.

The transceiver itself cost next to nothing, but I spent more than 600 euros to required components, spare parts, and other gadgets. You can buy a fairly good Japanese solid state radio built in late 80's or early 90's with that money. In terms of quality and performance there is no contest. The Japanese radio wins hands down. However, I was not only buying and repairing a radio. I was cherishing memories. In that context my Heathkit refurbishing project fulfilled it's purpose. Some day after many years I will sit in a rocking chair and look at the glow of the tubes recalling the good old times when I had thick hair and the bands were full of new ones. DX IS.