jcm800 4010 issue

[nico56]

Hello, i recently buy a 4010 combo from 1984 withe the vertical inputs .
Since i got it i had some volume loss and weird sounds, i chopsticked the amp and discovered that when i moved the grid stopper of the first EL34, the volume increased a lot ... I reflow the grid stopper resistor, retensioned the socket without success ..
Then i replaced the tube socket and the resistor and the problem remains .
This morning i cut the wire a little because there where a loop and it seems to be good know, nice tone and a lot of power !!

Did someone experiment the same issue on olds amp ? what do i have to check then ? The filter caps and bias cap were replaced with few resistor already .

(Sorry for my English, i'm French )

20191108_112641.jpg

20191108_112641.jpg

[martin manning]

The only thing I can come up with is that the extra loop of wire was causing an oscillation, which can be ultrasonic (inaudible), but significantly reduce the output. It could be that the wiring around the power tubes was moved around during servicing. Are the output tubes in good shape and reasonably well matched?

[nico56]

Hi Martin, yes it's quite unclear for me... but cutting a little bit of this wire in order not to have a sharp turn seems to solve the problem . My tubes are the Mullard EL 34 reissue, biased at 34 ma and 36 ma .

[nico56]

My power tube are new and i tried a pair of new JJ EL34 and the problem was still there

[M Fowler]

Broken wire perhaps?

[nico56]

Yes that's what i think, it might be broken because of the Sharp turn and the vibration

[pdf64]

No I think that a break in the wire would cause different symptoms. eg the tube would redplate.

[nico56]

When i moved the wire the sound increase to it's normal level, instead of beeing very weak and buzzy . The first time i played withe the amp, i was amazed by how hot the tubes gets, i could smell it from a distance so maybe they were redplating, ...???