Keith G wrote:
"Keith G" wrote in message
...

(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday), so perhaps you could rummage your 'valve
savvy' and assist me with a problem?

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in
90 degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad
distortion kicks in I'm told. Any immediate ideas where to look as to
cause? I have both amps here and can make comparison measurements -
I'm told all the passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!

:-)



Actually, it's even worse than that - I would like to rip all the 'bias
meter' palaver out of 'em and change them to cathode bias.

(No idea how to do that, needless to say!! :-)


Again, depends on the circuit, you may not have enough B+ to do that.

--
Nick