Deluxe Reverb: slight distortion at low volume

[Pedro Vecino]

EDIT: Went back to the preamp tubes and it looks like V1 AND V2 could be the culprit.
I put all the stock GT tubes back in and it wasn't doing it. So then I went back to my new tubes one by one and noticed the noise come back with V2 and V1.
What would cause both of these to go at the same time?

I assumed that changing the preamp tubes was a step already given (!). Does not have to fail both. In the second triode their cathodes are connected together and the effect can be transferred from one to another channel.

[Jonny toetags]

They're just bad tubes. If they're "pulls" there's a reason they were pulled. If they still have gain and aren't grossly microphonic many people would sell them as useful. If they're NOS I could only speculate that they were part of a bad run. Which might explain why they were never sold when they were made, but not how they ended up being sold as NOS. If they're Russian tubes all I can say is that I've had many bad ones right out of the box.

The only tube I've had do what you describe was a Telefunken smooth plate pulled from an old stereo amp. That tube also made it so I still had the low distorted signal with my guitar volume turned to zero!

I had Tung Sols in there.
I had some spare JJ's I put in for now.

[Chuck H]

Russian tubes then.

The thing to check for is DC on the grid pins of those four triodes with the Tung Sols installed. DC on the grid pins would indicate a leaky tube or a leaky coupling cap. It they are leaky tubes you'll just have to toss 'em. This is likely since different tubes fixed the problem. Be certain that it's both tubes that are actually leaking before just tossing them though.

[Jonny toetags]

What pins are the grid pins on the preamps?

Russian tubes then.

The thing to check for is DC on the grid pins of those four triodes with the Tung Sols installed. DC on the grid pins would indicate a leaky tube or a leaky coupling cap. It they are leaky tubes you'll just have to toss 'em. This is likely since different tubes fixed the problem. Be certain that it's both tubes that are actually leaking before just tossing them though.

[Jonny toetags]

Yeah I know this amp.
The plate resistors in the preamp should be replaced.
If it were mine, I would replace all the resistors in the audio path w/ good ones.
This is what makes it sound fuzzy and buzzy...cheap resistors.
It's not really the tubes at all.

Also, the output should be biased on the hot side, that helps a bit.

Recommend F&T caps for the power supply filters. Dump the Illinois Capacitors, they make it sound awful.

You play a note on the guitar and at first it sounds normal, but as the note decays...and the volume drops...
You hear a "bzzzzzzzzz" (if you listen closely) kind of distortion, at the end of the note decay.

That's really what it's been, resistors in preamp for sure. I've had several w/ the same symptoms.

Once again, this is not verifiable with a sine wave and O scope. You won't see this in a standard bench test.
ONLY testing with a GUITAR, will you actually detect this problem. LISTEN very closely, with a GUITAR.

I put in the F&T's. I couldn't find a 100V 220uF, so I put a 300V one instead. It's sort of big and the cap cover touches, but it works

Which are the preamp plate resistors?

[Chuck H]

The preamp tube grids are pins 2 and 7 of the preamp tube sockets. The plate resistors are those connected directly to pins 1 or 6 of any preamp tube. The Fender reissue Bassman did have some trouble with these resistors. IIRC the first year or two for that amp used 1/4 watt plate resistors and they would get crackly/noisy or sometimes just fail. I haven't heard of any issues with later reissue Fenders. I agree that the F&T caps are likely better than the IC brand. I've never used them but I've replaced a disproportionate amount of IC brand caps. They're cheap caps and you get what you pay for I suppose.