HELP fixing an old 100W Plexi clone

[w437776]

So, I got this amp 2 years ago, traded a ProCo Rat clone and 6000 dinars (about 70$) for it. Great plexi tone and very loud. I think it was made somewhere in Yugoslavia, probably in the '70s. It has some weird tubes in it - 3xECC83, 2xEL503 and one ECL82. Had no problems until now... Turned it on the other day and there was no guitar sound, just a moderate hum that got a bit louder by turning the volume knob. I tried changing the preamp tubes but no good. Any ideas?

Pics:
http://i43.tinypic.com/n6rl8o.jpg
http://i39.tinypic.com/10oegrn.jpg
http://i44.tinypic.com/m79yls.jpg

[Reeltarded]

Ideas? Bad electrolytics. Corrosion in tube sockets. Bad ground. Delaminating transformers.

Humm? What does the hum sound like? Is it all low hum, without any "eeeeeeeeeee" along with it?

The good news is that it's not filthy, or hideous!

[martin manning]

Do you know what circuit it is? Have a schematic? Usually a good place to start is measuring the voltage on all the tube pins and the power supply nodes. Shooting-from-the-hip guess is a rectifier or filter cap failure.

[Structo]

Whoa!

That is strange looking!

Is this a Soviet Union built amp?

[Cliff Schecht]

Those transformers need to be checked. They look in rough shape, as does the rest of the chassis and circuit really. This amp is a prime candidate for a complete rebuild :-/.

[Lynxtrap]

I agree with the transformers.
But the amp worked and now it suddently doesn't. Something happened, and that doesn't mean you should start rebuilding the whole amp.
To me it looks like it could be made in the 60's, but who knows. The thing might be rare. And they didn't spare any expenses when it came to wires

If you know what you're doing, measure voltages like Martin says. Otherwise you should leave to a tech.

Those EL503's are obviously rare, but they can be found. At least TAD have some of them for sale. For more money than you paid for the amp, of course .

[Phil_S]

Those EL503's are obviously rare, but they can be found. At least TAD have some of them for sale. For more money than you paid for the amp, of course .

Hmmm...consider where he is, Dinar = Iraq. Tubes available are likely to be Russian or Chinese. My thinking, if possible, is to drill out the magnoval holes and put in octal sockets. Chinese EL34B sound OK and should be among the more affordable tubes. First things, first, though. Maybe the EL503's are still good and the problem is elsewhere. Don't solve a problem that doesn't exist.

[w437776]

Dinar = Serbia. It would be really strange if it had gotten to Iraq all the way from here. I'll try cleaning the inputs and tube sockets first and then measure the voltages.

[Phil_S]

Dinar = Serbia.

Opps! That's what I get for believing the internet. See: https://www.dinarbanker.com/

[Lynxtrap]

The way the problem occured, I'd look for faulty components. But you never know, and cleaning never hurts.

I didn't mean you should buy new output tubes. But it's bound to happen, sooner or later.