Tremolux Amp repair FINISHED

[xtian]

Does this mean you're bypassing the preamps and still getting the problem?

It means I'm inserting the sine wave right at the PI grid. Do I understand you correctly?

[Firestorm]

Yes. And it still fizzes?

[xtian]

I can't answer that. When using a guitar to test, that's when I can perceive the fizz. But when using the sine generator to test, I'm using my eyes instead, and I can see distortion, but I don't know what it sounds like, and also I can't perceive whether it's quick-onset (the bad fizz is quick onset) or slow and natural.

I'll post some photos of my o-scope in action if it would help. What would you like to see?


Is there any possibility the OT is bad in a way that causes this ugly distortion any a given volume above a threshold, but sounds OK when played at low volume?

[Milkmansound]

Plate stoppers?

[xtian]

Plate stoppers?

I love it! Never heard of that before. I put in 100R, 2W plate stoppers, connected directly to pins 3. Sadly, no change.

[Firestorm]

I don't suppose you have separate preamp you could use inject a guitar signal into the PI to isolate the problem to pre or PA? I've typically found this noise to be preamp related, but you have it equally on both channels.

[Milkmansound]

I find it easier to go the other way. Grab signal from the output of the PI and put it into a mixer or powered speaker

Bummer about the plate stoppers. Thought that was going to be more helpful

[Firestorm]

I'm pretty sure it's preamps. This is clearly parasitic.

[xtian]

I find it easier to go the other way. Grab signal from the output of the PI and put it into a mixer or powered speaker

How? The PI has only half the wave on either plate.

[xtian]

OK, I'm determined.

I disconnected the preamps from the PI. Now nothing is attached to the two 220K mixer resistors going into the PI. I put a 1KHz sine on one of the 220K mixer resistors. As soon as I turn the sine up past 8 or 9v p-p, I get this ugly, ugly distortion. First image, below, is post output transformer, second image is post PI.

As a final test, I pulled the power tubes. So now the only tubes installed are the rectifier and the PI. See third photo, below. The wave is clipped, but doesn't look ugly. Does that look like OK distortion?

What do you guys think? Where is the bad distortion coming from?

[Firestorm]

Looks like normal clipping. I said it before: original Fender wiring works on half of these. You've gone all shield everything. And I also said shield the tone stack wiring. You've got nothing close to a stock Fender there.

[xtian]

Looks like normal clipping. I said it before: original Fender wiring works on half of these. You've gone all shield everything. And I also said shield the tone stack wiring. You've got nothing close to a stock Fender there.

Not sure what to make of your comment about shielding the tone stack... the tone stack is not involved now, nor any of the preamp stages, nor tremolo, but I'm still getting a horrifying nasty wave at the output.

[Firestorm]

Doesn't look too horrifying and nasty. It's clipped and there's a crossover sign, after clipping it looks. So i think the problem is pres.

[JazzGuitarGimp]

I think you've got a problem in the PI. Notice how the negative peak bulges down out of what the waveform looks like on the positive peak (second photo)? I've seen this in Merlin's preamp book. It's an unwanted distortion, if I recall correctly.

[JazzGuitarGimp]

It also looks like you've got a bit of crossover distortion in the output stage (first photo), which might indicate cold bias. But I think I'd concentrate on the PI issue first.