Can bias affect overall volume?

[Mindseyes]

My buddy recently picked up a Marshall JVM and it doesn't seem to have the volume that a 100watt tube amp should have.

I have read that these amps can come from the factory with the bias set very cold, can this have any effect on the over all "loudness" of a amp.....what else should we be looking for?

[murkat]

Bias, no.

tube output, yes.

http://www.mesaboogie.com/US/Smith/biasadjust.html

[seeker]

Yes it does, but not a whole bunch (such as twice as a loud). That's assuming it's biased in the acceptable range, but cold. What you really need to look at is a) tube type plate voltage and then c) cathode current

a) tube types have a max dissipation; for EL-34s its 25W per. 70% of that for an A/B amp (marshall) is a safe range.

Plate voltage changes as you change the bias and is part of the dissipation equation

c) cathode current is what most rule of thumb folks state. But, without the plate voltage, you could be waaay off.

Look at here and here

The problem is measuring both can be a hassle. I got one of the AMPHEAD bias probes, and they're just the best.

[Roshark]

Great read MurKat . Thanks for posting that link.

[FrankieIII]

Worn power tubes, worn filter caps, impedance mismatched, inefficient speaker(s), wall voltage fluctuation, etc....

[Armitage]

Bias, no.

tube output, yes.

http://www.mesaboogi...biasadjust.html

Beauty.