JCM 900 Problems

[willshep]

Thanks for your reply.

Yep, good point - i'll know more this weekend - i don't think there's much i can do now without replacing that component out and see what happens - not being any good with a soldering iron, i'll leave it up to a friend of mine !

Thanks again,

Will.

[willshep]

Hi,

All fixed - replaced all of the caps that form the bias circuit and now works fine - turns out that bias was dropping way down to -15 - valves weren't happy about that obviously - now all fine - so thanks again for all your help.

Regards

Will

[Alex R]

Great, I'm glad it's sorted.

- it's easy to get distracted by apparent myriad possibilities inside an amp, and indeed expert recommendations outside it, but most of that is electronic hypochondria and there's a real need for rationality. Everything in an amp happens for a reason, and there are always chains of logic to follow. Red plates - overheating valves - bias problem - check bias supply. Generally when troubleshooting you find a place where the problem is happening (in this case, inside the valve), and trace it back along the circuit until the problem disappears (in this case, at the unfiltered 'raw' end of the bias supply).