Snap crackle POP

Fez

And then ....Silence

It would appear that my JCM900 blew a power valve

http://i1277.photobucket.com/albums/y494/maashto2/070_zps3f2407c1.jpg

jpfamps

A correct assement.

The white in the valve on the left is (mainly) barium oxide and is indicative that the valve has lost vacuum.

Usually all that's required is a new HT fuse, new valves and a rebias, although if you use the same grade of GTs then (assuming that the amp was correctly biased when these valves were installed, a rebias won't be needed.

ICBM

More likely that the valve blew by itself .

(There is a difference!)

There's a crack in the glass somewhere. Pretty much the only way the amp could have caused that is a bias failure leading to the valve overheating.

Throw away the white valve, move the good one into the socket the white one was in, replace the blown fuse, and try the amp while watching the valve carefully. At the first sign of it overheating, turn off and get it to a tech. If it doesn't, chances are the amp is fine and you just need a pair of new valves. (Keep the old one as a spare.)

Fez

I have spare valve from last time they were changed (Physical damage that time, about six years ago) but I think it's overdue a service and may opt for cheaper valves as it's no longer my main amp. A trip to Henk it is then but not for a couple of weeks had some other domestic appliances fail recently leaving the credit card a bit battered. No rush though. Actually 3 sets of valves in twenty years isn't bad.

Fez

So Henk has the beast and has re-valved it but it also has a problem as yet undetermined with the Pre-amp. I may know more tomorrow.