Collins 20V-3 AM Broadcast Transmitter Restoration

A Story About The Restoration Of Collins 20V-3 sn#181

   For years now, operating earlier vintage radio equipment has continued to be a serious passion for many amateur operators around the world, including this author! For many hams; hollow state and vacuum tubes remain synonymous with the word “vintage”. “If it doesn’t have tubes and it doesn’t glow in the dark, it ain’t real radio!” The Collins 20V-3 broadcast transmitter glows in the dark.

   And even more serious “vintage” radio enthusiasts have a mad passion for the one and only, “Angel Music”, AM phone. For many of us in the hobby, we began back in the day with AM phone and even though we progressed with the times, our hearts have remained with amplitude modulation, “Angel Music”. Listen to a beautifully running Collins 20V-3 and you'll understand.

   Collecting, restoring and operating vintage gear is nothing short of; passion, obsession, even love for the beautifully crafted and engineered American made communications equipment from a different era. For many of us now, it’s a way to reminisce over simpler times, recapture our youth and now own what once we could only dream of having.

    For many amateur radio operators, owning a real AM broadcast transmitter and using it on the ham bands, is the ultimate expression of AM. Listen in on any of the popular AM frequencies and you’ll probably hear them. Today it’s become some what of a fad to own a broadcast transmitter.

   But long before it became a popular fad, back 15 or 20 years ago, only a handful of the elite vintage collectors and more specifically AM enthusiasts, had a handle on owning, restoring  and operating a real AM broadcast transmitter on the ham bands. These were the serious and well respected collectors of vintage equipment who operated AM.

  I have had at least one vintage AM station on air in my station for at least 30 years now. At times there were very few other enthusiasts to work on the bands. We were a close knit group and most were very experienced and knowledgeable on most every aspect of circuit design, restoration and operation.

   About 16 years ago I began studying, researching and collecting broadcast transmitters and all of the associated audio equipment to compliment their operation. Today I have only three remaining in my collection, a Collins 20V-3, a 21E and an RCA BTA-1MX.

   The Collins 20V-3 pictured here, I have very fond memories of. This one, serial number #181 was the first of a number of Collins 20V’s that I collected and restored. I acquired this piece, site unseen from a station in California in late 1993. It was supposedly in operational condition, I don’t think so!

   I had enough experience with collecting BC transmitters by then, so it was no surprise and I knew that I’d have to do a full ground up on it. You can probably see in the photos that this transmitter was in a dog house by the tower which had flooded! There was a water ring all the way around and about three feet up from the bottom of the transmitter and the interior was full of mud and a few dead rats, nothing out of the ordinary for an old BC transmitter project.

   Collins 20V’s are very simple basic transmitters and by the time that I finished a ground up resto on this transmitter, I was an expert on Collins 20V’s. I’m not one to just give my transmitters to someone else to restore. I expect to do all the work myself, teach myself what I need to know and to gain the personal accomplishment of knowing what I’ve achieved. To me personally, that’s what a real ham is all about.

    I was lucky to have the original manual and Collins build documentation for this transmitter. Checking the transmitter visually, I could see there had obviously been a HV short that wiped out some of the wiring. Not a good sign to start with and I had no idea if the iron was good.

   This was what we call a late box. You can tell by the very massive plate transformer, which was a Collins update in the final production runs including the oil filled mod transformer. The plate transformer is much larger than the iron in a V-2 or early V-3. This transmitter also had the full remote panel which was a Collins option as well as the motor driven power trimming option, nice. It was all original, albeit, in bad shape.

    I began the tear down in early January 1994. The iron appeared to show no shorts in the plate, mod, chokes and filament transformers. I’d go through the low level supplies later.

   The photos don’t fully show the extent of the disassembly, but I took it down to basically an empty cabinet. There was a hole in the lower side area that was not part of Collins design! I would have to metal finish this which I did in the garage in between working on the various chassis. I go through each chassis one by one on a resto like this. Unlike other collectors, I do not start tearing out all the original caps and replacing them. I’ve done more of this type restoration than many others and I prefer to keep everything as perfectly close to original as humanly possible without sacrificing original operating specs. Only a few components were too far out of spec or excessively leaky.

    I decided this transmitter would go on 160. Back then we hung out on one frequency, 1885. After I refinished the RF tank assembly and housing, I calculated tuning and resonance and reconfigured the tank to resonance. The low level tuned circuits in the 20V’s can be easily retuned. For 80 meters, I would remove the original plug-ins and build exact replacements from scratch. This, I feel, is the proper way to retain the original cans untouched. It's not required for 160 meter op.

    For 160 I knew from experience that I’d have enough drive to kick the transmitter and keep it stable after retuning the low level stages. I had a number of the latches and hardware re-cadmium plated as required and I refinished a number of smaller components to absolute original finish. For exterior or interior paint finish, I never just re-paint everything. I prefer to keep a piece as original as possible. On this transmitter, I would have to refinish the cabinet top, sides and the front doors. Everything else I kept original and only color polished. I do my own paint work and I had a professional painter friend of mine come over to polish the paint work after I let it cure out for 30 days.

    While the paint was curing, I began the re-assembly and re-wiring. I work from top down on these transmitters. When the exterior finish was completed, I completed assembly of the HV sections, including rewiring and re-lacing all of the HV wiring and calibrating the circuit breakers and time delays.

   The final week and it was time to light up the low level and see if she would come up to resonance and then check the audio low level. Everything as I recall was fine and now the most exciting point when you bring up the big supply. I found the first problem, the HV wouldn’t come up. Not good!

    I remember sitting there all night going through the schematics trying to figure out why! I enjoy this part as it challenges my thinking to research what’s wrong. I won’t ask for help until I’ve tried my best to do it alone. I saw something on the schematics that lead me to feel that I may have a bad ground connection somewhere, holding up the interconnects which left the control circuits latched out. Sure enough, that was the problem.

   On the second week in March 1994, I lit her up and put serial number #181 back on the air. That was exactly 30 years to the week that this transmitter had its final test check out at the Collins plant and sent on to delivery at its new station home.

   For an old vintage radio collector and restorer like me; self taught and working alone, it’s hard to put into words what it’s like when you try and when you succeed in accomplishing something special that you can be proud of, even if no one else ever knows.

   I hope you have accomplished or will achieve the same with your hobby. 

       

Author: Mr. Gary L. Goldsmith, W6UH
For: MyHamRadioSpace.com, 2008