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*I strongly suspect that a lot of the "improvement" peeps claim to hear from replacing 34's and especially '84's with L6's or V6's is due to the fact that the rest of the amplifier has to work about twice as hard for the same subjective loudness.
I just replace all the valves in the amp, and was getting a reading of 93mV, which I thought was way too hot, So I brought it down to 63mV which might be too cold, as the amp now has a lot of background noise when I play certain notes ( notably the A note, sounds like someone whispering a loud "R" behind the note)
I used a matched set of Harma retro cryo EL34's in the power stage.
As for the noise can't really help you., miccy new valve? It is certainly nothing to do with biasing.
*Except the HT-20 which is set for 11.5 volts across one of the 220Ohm "cement" cathode resistors.
That does sound suspiciously like a microphonic power valve. Put the old ones back one at a time and see if it goes away when either (or both) of the new ones are out of the amp - don't worry about biasing just for this test.
"Just because I don't care doesn't mean I don't understand" - Homer Simpson
I have now adjusted the bias to 50mV.....but the background noise is as bad as ever. I will try to replace the output valves one at a time and see if this helps.
If it is a case of a microphonic valve, will Watford valves replace it? The valves are new, only bought them in september.
I swapped out the power valves....one at a time. After the first one swapped, the background noise was still there but not half as bad. After I swapped the second, it disappeared altogether.... So it would appear that both EL34's were microphonic. I will have to send them back and just bias the old ones again until the new ones arrive.
Thanks for your help ICBM and ecc83!
and sorry for hijacking this thread.