Marshall JCM600 Blows Fuse intermittently

[Tech. Tom]

Hello: I found F101, Slo-blo 6.3A blown in this amp. I couldn't find anything that would have caused
it so I replaced it and it worked for a few weeks then it blew again.

I was thinking maybe one of the tubes were shorting out intermittently.
Any suggestions would be appreciated.

Thank you.
Tom

[Enzo]

That is a good place to start, yes. Pull the power tubes and shake them, do any rattle inside, and with the pins pointing up, do any have loose stuff rolling around in the glass at the other end? Look at the power tubes, is ther any discoloration of the label paint? Does one tube look different?

[Tech. Tom]

Good Idea Enzo. Too bad I can't use my Sencore crt restorer on the tubes.

[g1]

F101 is the heater fuse. If your line voltage is a bit high the fuse may be a little bit undersized.
A check of the heater voltage will tell you if this is likely. It should be about 6.3VAC, if it's much higher, your line voltage is probably on the high side.
http://music-electronics-forum.com/t31904/