Replica of my first Receiver kit in 1955
What's this among the piles of paper at an estate ? .....there, in my hands, was an original instruction manual for a "One-Tube Radio Kit", the AC-100 made by Air Champ, the first receiver kit I ever built when I was a mere lad of 11. The manual also contained a carefully cut out board component layout, complete with punch pricks to locate the screw holes on the 7" by 7" plywood base. I'll bet many of you had the same experience with this radio. This was also the radio kit Sears and Roebuck sold in the Cub Scout / Boy Scout department of their store. That's where mine was purchased. Took a long time to find the 22-1/2V battery but it was finally located in the hearing aid section.
Air Champ AC-100 manual
Naturally, the next step was scrounge a few vintage parts, heat up the soldering iron, and go for it. Most of the parts were located in my junkbox, even some vintage plywood from an old shelf unit which now has one cheesy particle board shelf.
Two unique things about this radio are that the components came with all their leads soldered, so no additional soldering was required. It used 19 Fanestock clips for all the interconnections (that used most of the box you had, thanks, Bill). The other unique thing was the minimal component count by controlling the feedback via tickler coil coupling. This requires some getting used to as you move the inner coil to control the regeneration. I used some electrical tape to make coil movement smooth. It uses a 3Q4 miniature tube, two 500pf fixed value capacitors (not critical), a 360pf variable capacitor, a switch, and one 1M resistor (not critical).
The original radio came in two versions. The "One-Tube Radio Kit" covered the Broadcast band only and there was a "Short Wave Adapter Kit" which had a frequency range from 1500Kc to 18,000Kc, using two separate coils. Was it a pluggable coil ? Air Champ also offered a "One-Stage Amplifier and Speaker Kit", the AC-300, which "gives loud speaker performance equal to any standard manufactured portable radio set".
Mine has been wound to cover the top end of the BCB up to 80m. Found a 8:1 vernier 360pf variable capacitor in the junk box, so I used that. The 22-1/2V battery is replaced by two 9V batteries which works just fine. "High" impedance headphones vary quite a bit and you NEED a set which measures 2000 ohms DC resistance or higher, anything less works poorly. The headphones ARE the plate load and the military H-32/U headset, at 3000 ohms, works well. In fact, "poor headphones" was the only problem I had with my receiver back in 1955 until a neighbor (Dan Weiser ...worked for GE?) came over with a higher impedance set.
Here are the details of the BC coil from an original AC-100:
Fun little receiver to build but it does point out some deficiencies. Mmmmm, I feel another Regen coming on ....with higher Q ceramic coils and tube sockets, and ...
Closeup of the receiver board
Component layout of the receiver board
Schematic of the AC-100 "One-Tube Radio Kit"
And what do you know, at the August 7th, 2004 Summerfest in Austin, in an old bucket
on a trailer in the outdoor swapmeet area,
an ORIGINAL AC-100 for the outstanding price of $.25. I doubt if anyone else knew what it was. This one is complete down to the untrimmed leads on the original components. The only thing I've added was a knob on the tuning capacitor and a 3Q4 tube. I'll just leave this "as-is" and put it on the shelf.
An Original AC-100