[sdiy] OT: $5 Wards Airline AM/FM radio cum guitar (synth?) amp (most likely)

[anthony]

The tuning contraption is a basket-case, but it has a phono jack input and 
it uses a 6V6-GT. It even has a real power transformer and a 5Y3-GT 
rectifier.

I can't tell what tube is supposed to be the preamp tube for the phono, but 
it may be the 12AT7, becauseit's right next to the jack and the Heptode 
front-end tube. The if chain's all rinky-dink 7-pin tubes and the audio 
preamp - at least for the radio part - is a 6AV6. Now I can't complain about 
this type of tube too much. I used an octal sort-of counterpart: a 12SQ7 for 
a preamp in a guitar amp I made from a couple different All American 5 
radios that sounds super with a 50L6-GT. I imagine the 6V6-GT will sound 
very similar since they look almost identical. How would a Tung-Sol 50L6-GT 
compare against a Raytheon 6V6-GT? How do the old brands compare? The 5Y3-GT 
is a Tung-Sol. I doubt a direct-heated cathode fullwave rectifier wouldn't 
make much difference in tone in a single-ended amp, even compared to a 
single 1N4007 that I used in the 50L6-GT amp. If it gets me less hum then 
that would really be something, because I barely have any hum and that's 
probably coming from single-coil guitar anyways.

But I digress...

At first I thought of restoring it, because it really is a cool looking 
radio in its awfully large bakelite case with nary a crack and ornate grill 
openings for the decent-sized speaker. But the dial face is melted pretty 
badly and the string came off of the big tuner wheel and I can't imagine 
having the patience to really do it properly. So I think I'll just use it as 
a secondary guitar amp because I really want a stereo rig. Not restoring the 
radio might leave open the possibility for some mods, like trading out the 
heptode for another twin-triode, maybe for a better tone-stack (maybe that's 
what the 12AT7 is in there for - I don't have a schematic yet...) and a 
cathode follower stage. A reckon I could even actually fit a smallish reverb 
spring; the cabinet's wide enough. Hmmm... And what about tremolo? I've 
never seen a tremolo on a single-ended amp that didn't use a pentode for the 
preamp (the Vox AC-4 used an EF86 I think...). Reverb would be enough of a 
job. I could use a brass plate where the dial plate went for Input & Ouput 
(Headphone or Direct-in) jacks & extra controls. Maybe an electric eye for a 
VU meter...

And it's that I don't have a schematic and the wiring, though the beloved 
point-to-point, is pretty sloppy and the quality of some of the parts is 
really questionable - that's pushing me to have it be an amp project. Some 
of the film caps actually look pretty good though. Only one loose 
electrolytic besides the big twistlock can (which I will probably still 
use - which leads to the next question:

How do you rejuvenate old electrolytics that have been sitting unused, using 
a Variac? I have 4 different Variacs - OK, they're all Powerstats, and one 
is a loose panel-mount jobby waiting for a case, but I have 3 variable 
transformers of various sizes and ilks. So is the idea to pull all the 
tubes, but the rectifier, and crank the dial up slowly? What voltage should 
I start at? I can forsee the problem of using too low a voltage to let the 
rectifier's cathode to get hot enough do it's job, so not too low, but maybe 
it's less of a problem with direct-heated cathodes? Plus it's not like I'm 
trying to fire the ENIAC back up - it's just one 4 x 40 uF twistlock can 
cap. Or I could buy 3 new 40 uF, 350V caps and 1 new 40 uF, 20 V cap.

Doesn't 350V sound a little low for a 6V6 or is it just higher in push-pull 
Class A/B amps where it's around 450V?