#1
Hey guys, I just got my old JCM 800 50 watt dual channel head rebiased with JJ EL34s and new preamp tubes. Before the tube change, (I had 6550s) this amp was headsplittingly loud and there was not much of a clean channel to speak of. After the swap, i noticed that the amp was significantly quieter, and I though that was just because of the different tubes, but then I noticed that on the lead channel, no matter what I do to the volume and preamp knobs, the sound is the same.

Do you guys have any idea whats going on here? I just do not have any sort of saturation/sustain coming from the amp. There's definitely gain, just not nearly as much as before, and I can't get the gain channel's volume and preamp knobs to work.

Any input?

Thanks
GEAR

Epiphone Elitist Les Paul Standard Plus
Marshall JCM 800 half stack
#3
I'd just take it back to the tech and "look man!" He shouldn't have let it out the door in that condition.
AL
#4
Take it back the the tech, the tubes could be lemons.

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drone/doom/post-metal: http://theygrieve.bandcamp.com
#5
What kind of preamp tubes did you use? 12ax7s, spax7, ecc83s?
If you start a reply with: I have never played one but I have heard good things about it! Your opinion is invalid.
#6
Its not the tubes, I replaced them with different tubes and it was the same. Actually none of the controls for the Lead channel work. I think this is a circuit board issue. Also the LED light that turns on when the lead channel is selected doesn't turn on anymore either. This leads me to think that the board is wired in series and there must be some misconnection early in the circuit so all the knobs and the LED are not working because of this.
GEAR

Epiphone Elitist Les Paul Standard Plus
Marshall JCM 800 half stack