Vintage Fender Champ 12 Red Knob Repair

[philbraden]

Hi - My Champ just buzzes like crazy after the main tube heats up - no signal throughput at all. Checked all tubes for continuity; heaters fine (I don't have a valve tester, but the amp was never used much). I can't find A+, but odd readings on B+ (417VDC as opposed to 496VDC) and c+ (297VDC as opposed to 242VDC). All diodes seem ok. I'm guessing one or more of the electrolytics may be duff, but if anyone has advice, I'd be grateful. Phil

[Chuck H]

Back story? Was it working and it broke? Has it been sitting unused for a long time and didn't work when you plugged it in? If so, did it work before it was stored? flash of light, puff of smoke, dropped from a moving car?

And please access and post a schematic that we can all reference for ease of communication.

[philbraden]

Hi - thanks for replying. Last time I used it (and was working) was probably 15 years ago. It has been sitting in a decent environment for 10 or so years, but no heating (in the UK). I fired it up a while back and it simply just started buzzing (no *puff* or anything). One of the input jacks was a bit knackered, so I removed IP1 completely just to be sure that there wasn't a short. There has not been any mechanical damage of which I am aware (never been gigged, case OK etc.). I'm using this (http://ampwares.com/schematics/champ_12.pdf) for the schematic.. Thanks for your time!! Phil

[Pedro Vecino]

Try with another 6L6.

[philbraden]

Ta. Have just bought a couple.. Fingers crossed.

[Dave H]

Here's the schematic. It does have quite a bit of single ended hum even when working correctly.

champ_12.pdf

[philbraden]

Here's the schematic. It does have quite a bit of single ended hum even when working correctly.

[ATTACH=CONFIG]50765[/ATTACH]

Thanks!

[yann]

I would test with another 6L6 as Pedro said.
But in the meantime you can remove the 6L6, and then measure B+ again. You should see something pretty close to schematic value, probably even more.
You can also mesure B+ with your meter in AC true rms mode. If you find several volts here that could mean you have bad filter caps in the power supply section.

[Randall]

A red knob Fender is vintage now? Good lord, I'm old.

[Enzo]

Yeah, sigh...

To me 1950s is vintage, but if you are 25 years old, a 30 year old amp is from before you were born. And that is what, 1988?

[The Dude]

Yeah, I remember doing warranty work on the red knobs.

[nosaj]

Yeah, I remember doing warranty work on the red knobs.

Ha , then would that make you vintage?

nosaj

[Randall]

Would it have killed them to include what type tubes are in there?