The Amp Garage

Lots of different champs throughout the years and I think the B+ was creeping up higher in the CBS era. Same power transformer was used for princetons, so maybe they were going for a compromise between the two, maybe they were trying to sell tubes so they didn't bother to rebias to compensate for th...

6v6 running at 14w isn't unusual for a champ, cathode biased amps are usually close to 100% at idle, somewhere around 90-95% is a good place to shoot for if you are being conservative. I often see stock champs that have been used for years in the 115+% range without issues. This isn't ideal, but som...

I would suspect a damaged pot and/or a bad solder joint. You shouldn't lose the ground reference at max volume if everything is wired as it should. Easy enough to measure, with the amp off, what resistance you get at max volume. Could be an oscillation, but my guess would be a bad connection. You co...

It is a ratio, not a fixed value.

But according to the tube charts, the output impedance of the various tubes I'm interested in (6L6, 6V6, 6K6, EL34 and KT88) vary substantially. So I don't see how one OT, whether it's primary is 5K or 7K ohms, can satisfy all of those different tubes. Is it just the case that either primary value ...

xtian wrote: ↑Fri Apr 12, 2024 6:41 pm some of their photos are clearly off-the-shelf fuses with colorful stickers wrapped around them.

By "sticker", I think you mean "UEF technology treatment".

does graphene treated surface mean they rubbed a pencil on it?

Plate looks like a plate, grid looks like a grid, cathode doesn't really look like a cat but they do hang out in the warm part of the tube. I suggest you redraw the schematic in a way that makes sense to you. You might want to draw different versions for each switching arrangement.

I got on here hoping I could get someone to say, “replace R-this, R-that and C-the other” so I would be going in with a set plan. Pretty sure that's what happened? No one can tell you exactly what is wrong without looking and measuring things, but you got your list of suspect r's and c's... R's: pl...

I don’t think you need to know the basics of how amps work to fix the thing, but if you haven’t spent some time reworking poorly designed single sided PCBs with too many thermal cycles, you aren’t going to have a good time. Pretty sure I have my 10k hours or whatever but still end up lifting a trace...

If it were a solder connection on the tube sockets wouldn’t it just effect the tube in that socket? All of the power tubes went dark and came back on together. They are in series. Bad plate resistor can cause static, bad solder joint can sometimes sound similar. Might as well change the plate resis...

Seems like nothing I am saying is getting through, but I will try one more time. The way the boards in that amp are arranged make testing very difficult, probably near impossible to do safely if you aren't experienced, so don't bother, just open it and start soldering. Even chopsticking might be a w...

Here is something new, before I went to try swapping out the preamp tubes one at a time with an extra I have, I turned the amp on to play a little. The crackle started immediately, then it went totally silent and passed no signal. I looked in back and the power tubes were all dark. After less than ...

Stephen1966 wrote: ↑Fri Apr 05, 2024 9:33 pm Do these boards become conductive?

Only the charred bits, as far as I'm aware.

Those hammond enclosures are relatively thin aluminum, so machining isn't too bad. More of a pain than predrilled, but you can knock something out with a stepper bit and a file pretty quick if you don't need to cut too many square holes. Nibblers or jewelers saws are nice for squares, but not necess...