Keith G wrote:
(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),

Chance would be a fine thing. I never got your email Keith. Anyway....

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'...!!


Without knowing the circuit its a bit of a guess, but my first thought
would be to check if the coupling caps have become leaky. (assuming
there are any).

Check the voltage between the 300b grid and ground. I would expect
something like -70v. If the coupling cap is leaking it will be higher
than that.

Have you considered painting the valve bases and sockets so he may be
able to work out what goes where? Or faining that, strike hime on the
head with the nearest outout transformer and tell him to get a clue?

--
Nick