spitfire problem

[thomasdj]

hi,

I have a problem with my spitfire clone. When the Master is turned higher than 1 or 2 (out of 10 ) volume ca. 4 and tone 6, one of the EL84 is overheating (glowing more than normal) and the amp fails; volume drops dramatic and the amp starts to hish (sounds a kind of overdrive to my ears).

Please help me.. what is wrong?

Thanks,

Thomas

btw: I run my guitar into an JMP-1 and then to the amp

[Mars Amp Repair]

well,
not familiar with the amp, but it would be really weird for the power tube/tubes to red plate as a result of the volume control position. Is the 'glow' on the gray outer metal part of the tube (inside the glass)?

It could possibly be a shorted power tube...but usually that results in sparks inside the tube & blown fuses.

Perhaps the first way to get some indication of what's going on is to swap the power tubes & see if the 'glowing' moves with the tube or stays with the same tube socket. Even then not too conclusive.

Are you coming out of the jcm-800 send to the input of the clone? glen

[Bruce / Mission Amps]

It could do this to the power tubes if, when turned up, it breaks into an ultrasonic oscillation...
The volume could drop because the tubes are being beat to death at a frequency the speaker can not reproduce.
You don't hear anything going on except the music audio dropping due to the power tubes being clapped out.
The tubes could be drasticly over driven in ultra sonic frequencies and they simply can not make any real audio anymore.

[thomasdj]

Hi,

thanks for your reply

I run my guitar through the input of the JMP-1 Preamp and its output to the clone input (...using the preamp as a pedal)..

I reversed the two wires from the OT to pin 7 of the two EL84 tubes and this actually solved the problem so far:S ..i had the amp going on for 4 hours at very high level whitout failure..and whitout the preamp at home! I am in the studio right now and the amp is placed in a very compact room due recording and so on.. After one hour the amp started to fail again (loud squealing).. I am wondering if this could be a heating or a dress problem?

best regards Thomas