JCM 900 4100 Dual Reverb head very low volume

[navdave]

A buddy of mind brought me his JCM 900 4100 Dual Reverb complaining of very low volume and fading in and out. This amp is for the most part solid state so I'm not totally lost
but this is uncharted water for me. I have checked all the tubes in the amp in another all tube amp and they are good. Three things I noticed right off the bat was that the clean channel is louder than the dirty channel, the bias when being read with my meter fluctuated while playing the amp from 30mA all the way up to 50mA but negative voltage to the power tube grids was constant. Third thing I noticed I don't know if they are supposed to or not is that the 4 LED's on the dirty channel do not glow when the high gain channel is engaged.  

[tubenit]

This may not be helpful to you, but when my good friend brought me his JCM900,  I gutted it and turned it into a Plexi 50.

He did not tell his band mates that he was having this done & from the get go (after the conversion) they all commented that he was getting the best tone that he has ever gotten.  He is a good player and his band once opened for Derek Trucks and also Dave Matthews.

I heard him play that amp prior to a conversion at a club and it sounded muffled.  After the conversion, the transparency & sustain was MUCH improved, IMO.

We even ended up keeping the original pots to keep cost low.  Total conversion in cost was around $115 from what I remember.

With respect, Tubenit