I've built my first ever homebrew radio using the 12AL8.

I started with Norm's 12K5 but decided I wanted to try my own hand and switched to a 12AL8, then added a 12EL6 audio preamp, all on 12VDC. The coils are wound on octal bases salvaged from dead tubes and the whole thing is mounted in a short CD case.

Schematic and pics are here http://s1243.photobucket.com/albums/gg546/flipperhome/12AL8%20Regen/



Band tuning is the right side small knob with the larger knob bandspread. That might seem backwards but the larger knob gives better control and bandspread is where one fine tunes. The left knob is regen. Antenna, 12VDC, and speaker/headphone connections are on the left side wall. Octal coil socket is on the rear.

Not shown is I also wound a shortwave coil and did my first ever 'shortwaving'. Since I don't speak Spanish, German, Japanese, or Chinese I'm not sure what all I heard but I did catch the station announcement for Radio Taiwan International on 5950 KHz. It works!!

Fine work there, Flipperhome! I've got the better part of a 12K5 regen built, but I have to make a custom bracket for a couple of the controls. I did mine somewhat the reverse of yours in that I made a chassis, for lack of a better word, out of a piece of copper clad PC board in the size and shape of a CD and am mounting everything on it except the speaker which will be at the top (tall CD case, in this instance.) The controls will be accessible through holes in the case and there will be knobs sticking out, but like I said, I have to get a bracket fabricated. I have this tendency to box myself in like this; otherwise I'd have had it done a long time ago.

Scott Todd

Thank you. The components cover up a multitude of sins as I basically hacked it together on the fly from spare parts using crude tools and the plastic was more trouble than I expected. I really spent most of my time on the circuit and learning about regens.

Like a carpenter eh?? Hide your mistakes...

I have to agree with Scott, at least in the picture it looks very nicely constructed...

Tom

You bet'cha The 'not round' holes are underneath 'good looking' stuff Even the blooming 9-pin hole punch didn't make a round hole. It 'snapped' out of round on one side.


I wasn't so sure before I mounted everything but even with me knowing where all the warts are they're hard to find now that it's all together.

The biggest surprise was I couldn't believe I actually found 'right size' mounting screws for the plastic 'transistor radio' caps in my junk screws bin. And four of them to boot!

I've uploaded a 36 second video showing my little regen playing through a speaker and tuning from BCB 740 to BCB 700 via the bandspread cap. Audio is a little bit better than the camera mic indicates, and these two are the 'loudest' stations in my area, but, remember, they're 12V tubes and max audio power is only about 25 mW. But that's enough to be quite loud in common 8 ohm headphones.

Time was about 7:00 PM and, what was interesting to me is, the 700 KHz station goes 'dim', almost as if someone threw a switch, about an hour or so later. I had noticed that before so I looked it up and turns out they do. Daytime power is 15kW down to 1kW at night.

Btw, Tom, per our previous conversation, notice the rising squeal frequency as it tunes off 740 KHz. It obviously does that in reverse when tuning onto 740 KHz, frequency drops as the station is approached, and on both sides of the station frequency, so finding a (weak) station is tuning for the beat frequency center null and then adjusting regen for best audio. However, the 700 KHz station was, at the time, strong enough to mask the heterodyne as it’s tuned in.

I've uploaded another video showing shortwave tuning from Radio Taiwan at 5950 KHz to another, unknown, station. That's a reworked SW coil with 14 total, 6 turns to tap, giving a tuning range, with a 47pF padder, of roughly 5.8 MHz to 7.6 Mhz. Given the discrepancy between calculated and measured, with my RF generator, frequency range, coil self capacitance must be about 24.5 pF.

All of these, btw, are with a 50 foot, or so, wire antenna tossed down the upstairs hallway, not exactly a 'premium' antenna layout.

Selectivity isn't so hot and my plain ole AA5 'with coils switch' Halicrafter's S-38E gets a ton more with an smaller wire antenna tossed on the downstairs floor and, of course, has more volume than you know what to do with. It doesn't fit in a CD case and run on 12 volts, though.

Hello Flipper,
Wow very cool