V90 Ch1 Tweed mode hiss

[philosopher]

So, tbh I initally didn't found the Tweed mode to be any interesting, so it was left alone.

Thought yday to give it another try, only to find out there's a serious constant hiss coming out the speakers, when engaged.

Switched to clean, hiss gone. Switched to tweed, hiss is back.
Took the cable out, gone. Put back, hiss again.

Increase volume/gain/treble, all result to louder hiss.
FX on/off/bypass makes no diff.

Sounds a lot like pink noise, not like tube noise.
In any case, I swapped all tubes one by one.
Unless two of them failed at the same time, tubes is not the problem.

Afaik all other channels/modes are unaffected, only ch1 Tweed mode has the issue.

Could be a resistor somewhere along the tube gain path?

Any similar experience?

 

[rarebitusa]

So, tbh I initally didn't found the Tweed mode to be any interesting, so it was left alone.

Thought yday to give it another try, only to find out there's a serious constant hiss coming out the speakers, when engaged.

Switched to clean, hiss gone. Switched to tweed, hiss is back.
Took the cable out, gone. Put back, hiss again.

Increase volume/gain/treble, all result to louder hiss.
FX on/off/bypass makes no diff.

Sounds a lot like pink noise, not like tube noise.
In any case, I swapped all tubes one by one.
Unless two of them failed at the same time, tubes is not the problem.

Afaik all other channels/modes are unaffected, only ch1 Tweed mode has the issue.

Could be a resistor somewhere along the tube gain path?

Any similar experience?

FWIW... from what I can tell briefly looking at the schems is M3, mode 3 relay for "Tweed mode" brings in C7 and R216. The tube voltages don't change for Tweed mode so there's probably not much else going on with it circuit wise. It may be one of the component areas to look at. In my V:90 Tweed is significantly louder then FAT or Clean and there is more hiss in comparison.