Silverface Champ Shriek/hum, overheating issue?

[edenexter]

Hi all! I'm new to the forums and I hope I can get some help here.

I have this nice little silverface fender champ with some issues that I'd like to repair.
It sounds great but some component seems to fail under a little too much heat. If placed near a wall, the amp is bound to overheat within 30 minutes making it very unreliable.

I also hear popping sounds every 5 to 10 minutes which eventually totally rips loose and becomes a loud hum at volume 0 or a hum with a nasty shriek when the volume is turned up.

My guess is the amp is arcing somewhere, but if anyone has any tips on where to look first I would appreciate it.

I have switched the 6v6GT tube for a new one but it still fails.

Thanks!
E

[Amp Kat]

Did you change the rectifier tube ? and check the Cathode resistor & Cap and make sure they are ok. That's where all the problems with these occur.

[edenexter]

I haven't replaced the rectifier, but I'll look into that. I'll also give the cathode resistor and cap on the 6v6 (you mean these rigth?) a check. Thanks!

[MWJB]

What do you mean, "placed near a wall", you should allow ample space around the rear of the amp to allow cooling air to circulate around the 6V6 tube. To reduce heat, bias the 6V6 cooler, SF champs often dissipate over 20W at the 6V6, an 800ohm cathode resistor will get you nearer to 14-15W. Your amp still has the original filter caps, change them, use discrete caps rated for 500vdc at the main B+ & screen supplies.

Your noise issues could just as easily be the 12AX7, you don't mention changing this?

[edenexter]

I'm sorry if I seem unclear. What I meant was that I found out for myself that heat was the issue because the amp would fail quicker when limiting the air circulation. It was an observation.

The amp still has the original 20/20/40 Mallory can wired up. I can replace it with discrete caps like you specify. I'll leave the can attached for looks and to cover the hole. Any recommendations on getting the new caps neatly into the chassis? I'm thinking about a small set of terminal strips that I'll bolt to the chassis (will need to drill holes though).

I'm taking it easy with replacing parts because I want to keep the amp as original as possible and I don't want to spend too much money just guessing which component it might be faulty. That's why I ask here

Thanks again!

[MWJB]

If the amp is failing due to excess heat, then reduce the heat...quickest & most effective way to do this is via the 6V6 cathode resistor.

Snip the "spades" off the can cap, then you can lie the new main (47uf minimum) & screen filter caps over the still in situ can, solder grounded terminals direct to tag on PT mounting bolt. Secure cap bodies to chassis with silicon, flying wires to board. Mount preamp filter at the other end of the chassis ground to input jack ground tag.


"I'm taking it easy with replacing parts because I want to keep the amp as original as possible and I don't want to spend too much money just guessing which component it might be faulty" fair enough, but you may also be keeping the faults as "original" as possible! You won't get anywhere with troubleshooting if the caps are failing...even if they are not causing the current issues, they are still not letting the amp work to its full potential.

[MWJB]

Also...don't use a 25v cap for the 6V6 cathode bypass, min 50v, preferably 100v.

[Gtr_tech]

That amp doesn't look too original to me.....I wouldn't be concerned with it. Do you want it to work or do you want it original?
Also, certain output tubes will cause problems in those. Never use a sov-wreck 6V6. Use old stock if you can get one, or JJ 6V will take what those dish out easily.