Need help. Tone problem...

[Nigel]

I've got a zinky Mofo amp, and I love the thing, and it sounds like the voice of god with mullard long plate 12AX7's (ANOS) and JJ KT77's.

Problem is, I have to bias the tubes up to 100% to get them sounding right.

The amp has 550V of plate voltage and probably 500 on the screen, as it has two 1K5W screen resistors.

Do I need to put a variac on it and get the plate voltage down? I hear the high B+ will cause an amp to make tubes run real hot to get out of crossover distortion.

Thanks y'all.

 

[glpg80]

whats the incoming voltage? have you looked to see if the PT was wired for a 10V lower difference primary tap that is not being used?

 

[Nigel]

120 at the wall. I'll check. There's a switch in the back from 110/220 or 120/240. Not sure what it says.

JJ 6L6, E34L, KT-77, and Sovtek 5881WGC have to be at or above 80% dissipation at idle to be of any use. Otherwise, icepick city.

Edit: After re-reading, not sure what you mean. Please explain!

 

[glpg80]

sometimes transformers are designed around 120AC but offer a 110V primary tap for hot outlets, and the same goes for 220/30/40 taps.

you could variac the PT but keep an eye on its temperature when doing so. by decreasing the primary you decrease the PT's internal effieciency rating for current supply on the secondaries. i would not go below 15V at first and check the PT - it should be luke warm at most, but never hot water warm or so hot you cannot touch it.