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

[Grant Richter]

>
> 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.
>

I have always started at zero and increased the Variac by 10% each  
minute until I reach 50%. Then I soak it at 50% for about 5 minutes,  
if nothing smells overheated, then increase 10% each minute up to  
full voltage.

Keep your nose over it and see if something starts to smell "hot" at  
any point and investigate. A "really hot" smell means power down  
immediately and check the electrolytics with a DVM.

I use a Variac to bring up anything slowly, if it has been sitting  
unpowered for more than 2-3 years. Even ARP 2600s and later solid  
state devices. Also amps like Phase Linears.

I do know that electrolytics don't like to be hit with full voltage  
after sitting unpowered for a few years.

I just restarted a free Polymoog which had been siting idle for more  
than 10 years by that method. We also cleaned and reseated every  
socketed chip and every single connector (with power off, of course).  
Result = completely dead to start with, about 80% of keys working  
after 3 hours of cleaning. There is some kind of velocity circuit  
that still seems funky, I didn't even start to look at the service  
manual until after hours of basic cleaning and deoxidizing were  
finished. There is an insane amount of stuff inside a Polymoog, but  
it came up in tune, after being completely dead.

The Polypedals really make that instrument cool though. Hit the pitch  
footswitch, give it two forearms on the keyboard and run the pitch  
pedal up and down. Yikes!!!