My First Homebrewed Amplifier          

(Darth Vader builds his first light saber...)


As any hopelessly addicted radio geek knows, a big part of the CB experience involves experimenting with your radio(s) to see what you can get them to do (usually things they're not supposed to do), experimenting with antennas, and building radio-related projects.  My Off-The-Wall project page is full of examples of such endeavors.  The Poor Man's BFO, Poor Man's VFO, and Poor Man's Reverb were typical of my mid 1970's era projects, back when I was a teenaged kid learning the ropes of radio and R.F. theory.  But while they were all fun and educational projects in their own right, none of those compares to my first homebrewed R.F. amplifier.  My 1st amp was both more complicated and potentially more dangerous than any of my other projects up to that point.  But while the odds may have been against me,  somehow I pulled it off.  God must have been smiling on me, or maybe Mr. Murphy took pity on me, and decided to bother someone else.  In either case, I managed to learn a bunch of important stuff and had some fun in the process. I'll start this story by first getting the disclaimers out of the way. The CB radio service was never intended to be a hobby-use band for chit-chatting and experimenting. The FCC specifically promotes ham radio for that.  CB radios are designed to be low powered and relatively short range units.  You are not permitted to transmit with more than 4 watts of output power.  But be that as it may, the CB band did evolve toward quasi-ham, hobby type behavior.  Many people experimented with their radios, and quite a few juiced up their power by running external amplifiers, which greatly increased their power beyond the legal 4 watt limit.  Higher power enabled the operator to increase his usable range, and to be able to "get over" weaker stations who attempt to jam channel groups for whatever reason.  Also, the status of being a "Big Gun" on the block was an enormous ego boost, and there were a few who defined their very existence on the radio by their signal status.  There was also a "Keep up with the Joneses" rationale at work too.  If one or two people got amplifiers, then many of the others desired them as well.  With such an open atmosphere, many of us learned our first lessons in R.F. and radio on the CB band.  So while we were stroking our egos, we were also learning valuable theory.  However, children should not try this at home. 

For many of the aforementioned reasons, I obtained my first amplifier in 1975, a Contex 6706 in a trade for my "Bikemobile". This was a relatively small 2 tube amplifier which put out somewhere in the neighborhood of 75 watts of carrier power.  75 watts was good for about 2 "S" units of signal boost over stock power, which could make a significant difference when trying to reach that distant station, or when trying to be heard above the skip or jammers.  I became hopelessly addicted to the extra power very quickly and, most of the time, the amp was sitting with the filaments on hot standby, ready to be brought on-line with a quick flip of the switch, if the need arose.  Having that extra boost on the side tended to make me all that more willing to jump into on-air battles with both barrels, and it increased my overall arrogance (What's that saying about power corrupting?) and intolerance toward interlopers, which probably caused even more disputes in the process.  In essence, I had nearly become the very type of person we despised and fought against, the flip side of the same coin if you will.  Fortunately, I was only like that when trouble brewed, so there was still hope for me to be rescued from the dark side.  However, that wouldn't come until some years later....  

All went well for several weeks and as I continued to grow more dependant on my higher power capability, I became seduced by the power of the dark side. It was payback time to Uncle Albert for all the times he stepped on me when I ran my home made antennas, and for all the times he would play music while I was trying to have a conversation. I also enjoyed my first tastes of skip talking, working pretty much all the states east of the Mississippi (except for those too close to "skip"), and a few beyond.  Life was good, and I was enjoying my boost in station status.  Then one day, the worst thing imaginable happened.  Right in the middle of a small skirmish, the amp blew, with a quick snap and a wisp of smoke.  In the blink of an eye, I found myself stripped of my extra strength, much like Superman when he became "mortal".  The sudden cold turkey withdrawal from my extra power felt almost as bad as the time when I had blown the final in my Pace 223 and was forced to run 100 mW again, a year prior.  When I pulled the amp apart to troubleshoot it, with much relief, I found that the problem turned out to be an easy to replace R.F. choke and, after a quick trip to Radio Shack, I was back to my supersized signal once again.  But the whole event left me troubled.  It was an easy fix this time, but what if the next time it's something not-so-easy (or cheap)? I didn't want to be without the power (Where's that 12 step plan when you need it?), and feel somehow "demoted" in radio status.  So I started thinking that I wanted a backup amplifier, in case the worst did happen. This was a bit ironic in retrospect, since I didn't even have a backup for my one and only CB radio at that time, and yet I was more concerned about my amp smoking than my radio.  However, since I was just a 15 year old kid who did not have plentiful financial resources, I could not afford to buy another amp.  I had horse traded for the amp I had, and I was out of things to barter with.  So since I couldn't buy or trade for my backup amp, that left me but one other choice.  I had to build it.  A task which seemed much easier said than done at the time.  But I was more than willing to give it a try.

I started off on the daunting task which I had signed myself up for, by looking at the schematic of the Contex amp.  I figured I'd just copy that design, since it seemed simple enough.  It was a basic 2 tube (6JG6) single stage grounded grid configuration along with a single 6BQ5 tube for the R.F. keying circuit.  During this timeframe, I was a sophomore in High School and a first year student at the local Vocational Technical school.  In my electronics class, there was a virtual goldmine of parts, some new and some recycled from old television and radio chassis.  Back in the mid 70's, there were still many tube-type TV sets, which were a great source for power transformers, tubes, filter caps, and higher voltage parts.  I was able to scrape up a pair of 6JG6 tubes, 450V filter caps,  rectifier diodes, and a small 9 pin tube socket for the R.F. sense tube.  I also bought 3 bat handle toggle switches, 2 R.F. chokes,  and indicator lamps at Radio Shack (back when they had a good selection of parts). It didn't take too long to amass the majority of the parts that I needed.  But I still needed a power transformer and the variable caps for the plate tune and antenna load, and of course, a chassis to mount it all in.  But without these key components, my project was little more than a box full of parts.  So I was pretty much stalled.  But then I got a lucky break.  One of our locals, Steve, radio wiz and uber-packrat, bestowed on me the missing pieces of the puzzle.  I don't think Steve thought I had enough experience to actually complete this project.  Rather, I think he was just humoring me, or maybe he was challenging me.  In any case, what he gave me appeared to have been originally a Heathkit VFO.  At least that's what the front panel stated.  But it was now a practically empty chassis with 2 large 9 pin tube sockets, a power transformer, 2 SO-239 chassis mount coax connectors, and 2 tuning caps.   It was obvious that someone (Steve?) at one time tried to build an amplifier out of this chassis.  I don't know if it had been completed at one time and later stripped for parts, or it had been a project that never got past the stage it was in when I got it.  Whichever the case, it didn't really matter.  What mattered was that I was now well on my way to taking my project from the planning stage to the building stage.  

The first thing I did when I got my project chassis home was to wire up a power-on switch to the transformer primary in order to test the transformer. After all, if that didn't work, or it had the wrong voltages, it wouldn't do me much good.  The Contex amp's high voltage power supply put out about 850 D.C. volts with no load, so I was hoping for something close to that.  The chassis included a power cord, and a fuse socket.  So I installed one of the switches I had bought from Radio Shack and wired up the primary connection.  Once that was done, I made sure I had a proper amperage fuse, and I gingerly plugged it in and flipped on the power switch. The fuse didn't pop, there was no smoke, and I could feel the transformer humming ever so slightly.  So I grabbed my VOM and proceeded to measure the voltages out of the secondaries. There was 6.3 volts for the filaments, and about 700 volts with a center tap for the high voltage.  So far so good.  I then proceeded to wire up the tube sockets for filament voltage and grounded all of the grid pins and return side pins for the filaments. Then came the psychological moment of truth. I put my two fresh 6JG6 tubes in the sockets and flipped on the power switch.  I never saw a more rewarding sight as the tubes lit up for the first time.  I knew there was still a ton of work to do.  But seeing the tubes actually light up, made it seem all that much closer to reality.  Once I got over my initial euphoria, I got back to work.  One thing the chassis didn't include was the small 9 pin socket for the keying tube.  Fortunately there was a convenient hole to mount it in, so I installed the keying tube socket, and wired filament voltage to it as well. The hole was a little large for the socket, but I kludged it in there relatively securely with oversized washers.

Over the course of the next couple of days, I added the rest of the parts.  I mounted the HV rectifier diodes on two terminal strips. I added the high voltage filter caps and bleeder resistors.  When that was done, I was pleased to see close to 800 V D.C.  when I tested it.  At this point, I decided to deviate from the Contex schematic a bit and add in a Hi/LO power switch.  I made use of the center tap from the H.V. winding, to make the supply run at either 400 or 800 Volts.  I figured that half the voltage would result in half the power output in the low power position.  I wound a tank coil out of some stiff 8 gauge solid copper wire, the same diameter and number of turns as on my Contex. I also added a power on indicator light, a tuning light, and the standby switch.  I bought a suiable key up relay at Radio Shack, and connected the SO-239 input and output connectors to the relay with short lengths of RG-58 coaxial cable.  I completed the rest of the wiring and in less than a month's time of gathering and assembling parts, I realized that I had done it.  I had built an amplifier.  But putting all the parts together and getting it to actually work were two totally different things.  And most of my projects were never quite that easy............

Well the moment of truth had arrived, it was time to see if my homebrewed Frankenstein project actually worked.   I felt a surge of pride as well as excitement.  This had to be the most substantial homebrewed project that I had undertaken to date, and I couldn't wait to debut it for the world (or at least my neighborhood) to see.  But now that I was actually finished, I found myself with a case of cold feet.  I had visions of sparks, fire, and a ton of smoke erupting when I flipped on the switch.  So I checked and rechecked all of my wiring and parts placement to make sure there wouldn't be a large explosion when I finally put power to it.  Everything checked out and I couldn't put it off any longer, so I connected it in line with my radio.  A bold move considering that I could very well have blown the radio if the amp somehow took off in a parasitic oscillation, or fed high voltage back into the radio.  But I really didn't have any other choice, if I wanted to see if it would truly work.  Having connected the radio and plugged in the amp, I flipped on the power switch and crossed my fingers.  Like before, the tubes all lit up and it actually seemed like it was itching to make its papa proud.  Naturally, I opted to try it out on LOW power first, when I tuned it up for the first time.  So I held my breath, said a quick prayer as I flipped up the standby switch, and nervously keyed the microphone.  Since I didn't own a wattmeter which read past 7 watts, I borrowed one from Steve so that I could measure the power of the amp.  When I keyed the mic, the amp's relay clicked in, which was a good sign.  However the output power actually dropped.  Not good......  But I quickly tuned the plate and load capacitors and managed to get about 10 watts of power.  Wow! 10 whole watts out with 5 watts in.  Not hardly the bone crushing power that I had hoped for.  But I noticed that my plate tuning cap was fully open, so I started playing with the tank coil.  After manipulating the number of turns, I was able to get the power up to about 30 watts with the Plate and Load controls at a more reasonable 2/3 of their respective ranges.  I figured this was not bad considering I was still on LOW power.  So now I flipped the switch to HIGH power and keyed up.  A slight bit of retuning and I was hitting the meter with a little over 60 watts of power!  A little shy of what the Contex put out, but not bad for a homebrew amp.  I had just gotten through mentally patting myself on the back, when Murphy threw me a curve ball.  All of a sudden, out of nowhere, the amp started arcing. The loud, rapid-fire POP-POP-POP, sounded like a string of firecrackers going off in my room.  I was not prepared for this and it scared the bejesus out of me.  I panicked, and rather than do the simple thing and just shut off the power switch, I ran out to the kitchen and pulled the circuit fuse for my room.  I returned to my now quiet room and unplugged the amp and then restored power.  I could see where the amp had been arcing, and it seemed a little strange that 800V could jump a nearly 1/4 inch gap.  But it evidently could.  So I redressed the connections and coated the whole area with red "corona dope", which is supposed to prevent arcing in TV high voltage areas.  After letting the stuff dry for a day, I fired the amp up again and this time it worked flawlessly.   On the air tests with other stations showed clear modulation and no one could tell the difference between my home made amp and the commercially made Contex.  Not bad for my first homebrewed amplifier.

I was clearly quite proud of my accomplishment and not only did I make a big "to-do" about it on the air, I wanted to show it to Ralph at our next Explorer post meeting to get his feedback.  Ralph was my first real "Elmer", and he taught me a great deal about R.F. theory at our weekly meetings, so I had a great respect for his insight.  He was always giving me a hard time about being so fixated on (illegally) high power, but he also wanted me to learn the in's and out's of R.F. theory.  So I presented my pride and joy to him and stood back and waited for his critique.  Ralph pulled no punches and while he reluctantly gave me kudos for actually making this thing and getting it to work at all, he was critical of the neatness of my wiring (I think he used the term "Rat's nest").  Looking back, I think Ralph was secretly proud that I had built this thing and made it work, but he just didn't approve of illegal CB operation, and I'm sure he would have been far more complementary if I had build a one tube novice C.W. transmitter instead.  Ralph did offer up some constructive corrective suggestions on how to properly dress R.F. point to point wiring and H.V. leads and I promised that I'd clean it up, which I did.  

After all the work and time I spent building the amp, and my plan of using it as a "backup", it was not destined to be.  At the Explorer post meeting, while Ralph may not have been outwardly impressed with my amp, Dead Soldier (John) was, and he expressed an interest in acquiring it.  At first, I was not interested in giving it up (after all, I had just built it.)  But he offered that, if I implemented Ralph's suggestions to clean up the lead dress of the amp, he would trade me a new SBE Cortez for it.  Knowing that I would be of driving age in a few short months, and wanting both a spare radio for the base and a radio I could use for my eventual mobile (which as it turned out, would also come from John),  I couldn't pass up this trade opportunity.  So easy come easy go.  So we made the trade.  Luckily, as it turned out, I didn't need a back up amp after all.  John used that amp for a while, until he was forced to move to an apartment where he couldn't operate a CB station, and I lost track of him not long after.  So consequently, I don't know what ever became of my old amp.  I'd love to find it again, for nostalgic sentimental reasons.   It's also a shame that I didn't have the forethought (and a good camera) to take any pictures of it (so I could put them on a milk carton... "HAVE YOU SEEN THIS AMP?").  I'm guessing that my amp has left this world, having probably hit the trash bin sometime during the last 30 years, or it's buried in some dark damp corner in someone's basement somewhere slowly rusting away.......  I'll probably never find out. 

I would build 2 more tube amps in the coming years, one for LIM which, because of my slow progress on it,  probably cost me his friendship. The other I made for Jimmy (Streamer) from the Channel 13 group in the late 70's.  Jimmy's amp used bigger 6LQ6 tubes and put out close to 100 watts.  Combined with his elevation and Avanti Astro Beam antenna, his was the big signal in the King of Prussia area for the duration of the group.  Each time I built an amp, I got bolder with features, and the quality of my workmanship improved.   But it was that very first one which will always mean the most to me, as it was my very first.