The output EL84 (the last of my NOS Mullards from when I bought a bunch ten years ago) in my Rat Electronics Valve Special has been hard to dial in of late and I was thinking of replacing it. While fiddling around for the nth time I switched the preamp to the louder (hotter?) bias option and the overdrive tightened up, really lost the horrible flubby mud which had taken over.
Is this a sign that the valve has seen better days? It actually sounds pretty good in this setting which I was never a fan of before, but I seem to remember the amp sounding better in the past. It's difficult to compare with the assortment of tubes that have been in there over the years.
Comments
What is the 'bias' switch doing? If it's in the preamp it has no bearing on the power valve anyway.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
8. Three Position Preamp Valve ‘Bias’ Switch - Switches the Preamp ‘Bias’ between - ‘Negative Feedback’ -or- ‘Sharp+Clean’ -or- ‘Medium/High Gain’. Exclusive toRAT and fitted on All Amp
The amp sounds awful (on sharp&clean setting) when the power section is pushed hard, not so bad when the input gain is cranked instead. It also sounds bad when the power scaling is applied to the output valve, that's why I'd assumed that the output was the problem.
Using the more aggressive preamp bias is producing more output in the preamp section so the output is having an easier job for a given volume level. That fits in with the idea that the EL84 has had it.
Update:
Got an new JJ EL84 today and chucked it in: success. Cleans sound better, overdrive sounds better in all preamp bias settings, power scaling working extremely well.
I had been thinking of replacing this amp, but now that it's sounding good again I may think about getting it a proper cab instead of throttling it with the little 8" combo speaker.