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Thanks JohnDNJ - I think you are probably right...the manual only talks about the outer sockets, but I thought I'd give it a try. I'll call them Monday - egdon

Hi - I have a MkIVa from 1991. I know I can put EL34s in the outer sockets and run it in ClassA to get more of a Marshall-style output section, and I'm doing that now. I have EL34s in the outer sockets, and 5881s in the middle sockets, which seem (?) to have a slightly less powerful, more...

Last night, it happened again, and I was just lucky enough to notice that it was the silent record switch - you hit the nail on the head. Thanks Restless Rocks

So, I brought it in. Turns out there was a blown trace on the board that burned a resistor. They jumpered it, replaced the resistors, and it worked. Also turned out that the guy who had repaired it years ago had put in a bias trimpot, and they removed it and put it back to stock. New power...

I tried all different modes, tweed/full, classA/simul, triode/pentode...I think I have a bigger problem as you said. Today I contacted the tech and I am going to bring it to them and get it done right. I like to troubleshoot and such, but I don't want to take any more chances with this amp...

I have definitely had that problem today - putting the JJs in V2 or V3 would reduce the volume, but would cut the distortion too, and with a JJ in V3 my lead channel was clean. Swapping the old ones into those sockets has helped, but the amp still is very low volume.

thanks guys! That does make sense, and removes one more variable from my troubleshooting. Kinda explains why I couldn't find it in the manual...the manual with the pictures is for the B, which has a different loop/satellite sections. My manual is the typewritten one Really appreciate the...

Hmm. I just looked closer at the jack...it has two wires, brown and red, and they terminate on the circuit board in the corner, marked "BN" and "RD". So maybe it is stock. Weird - I have no idea what this jack is for

Thanks Kiff. I think my best bet is to call the tech tomorrow. Just was hoping someone might have had the same issue and fixed it [not wishing repair costs on anyone, hehe] So I guess that means the jack is definitely not stock, right?

Hi I'm having some trouble with my Mark IV - hoping someone can help point me in the right direction. A long time back, it crapped out on stage...some smoke came out of the transformer and the sound went to dirt. Had it repaired/retubed at the time, and it worked, but it never quite sounded...

Hi - I have a Mark IV A, 1991, and I've been having problems with it. In the course of changing tubes around I noticed a 1/4" phone jack just under the loop select switch, on the underside of the chassis. I cannot find this jack on any manuals or schematics I have been able to find. Anyone...