Problem with Bassman Build

[Structo]

If those numbers are correct, I think you may be a little low on the bias.

(W * .7) / V = I

W= wattage of 1 tube

V= power tube plate voltage

I = bias current

The 5881 tube seems to vary on the specs.
But most of the data I have seen rates it as a 23 w tube.

So 23 * .7/ 440 = 36ma

So that would be the high range.

You can usually go down to 50% easily.

23* .7 / 440 = 26ma

Some amps sound better biased colder, while some sound better a bit hotter.

Also be aware that the bias setting can change the plate voltage.
When you pull more current with the output tubes the voltage can go down a bit.
So it's a bit of a back and forth routine.
Set bias, measure plate voltage, adjust as necessary.

[philster]

Thanks Gents - been playing her for an hour this afternoon to bed her in. Seems to be holding up nicely and I'll double check the biasing tomorrow - thanks for the info!
Funny how Fender amps sound great with Fender guitars - plug in a Gibson and all of a sudden the "perfect sound" you had dialled in sounds rubbish. I see a period of learning is ahead of me (again!).
Cheers
Phil