Hello GBC, I’ve still got some issues with my tube amplifier ( Carvin X100B ) and am in need of a bit more advice. I think I got rid of the motor-boating problem by returning the stock pre-amp circuitry to its original configuration. It turned out that when I had modified it previously, I was using the wrong version of the schematic and it was over-driving the op-amps that affect the tone controls. When I say “I think…” I mean that the new problem prevents me from actually being able to tell whether it’s there or not, but the limited time it worked, I didn’t hear the boat.

The newest issue now is that there are very noticeable volume fluctuations. This was happening to a much smaller degree before while I had the motor-boating issue but now it’s more prominent. While playing, it will initially sound good but then the volume will drop and it loses all of its high-end. The best way for me to describe it is if you were to take a pillow, and hold it over the speakers. You can still hear the guitar, but you hear mostly lows and mids. Very little treble came through even after I cranked the treble knob, which usually gets very shrill if turned up too high.

Now, I did a lot of research this morning and I’m well aware that it is most likely a tube issue. Tonight I will be doing some tube swapping, focusing on power tubes (pulling one from each side and swapping them around) and the phase inverter preamp tube. What I need is for any other ideas and most likely culprits aside from tubes. I’ll be getting some parts to fix this soon and would prefer one order with any and all possible parts than several different orders. Here’s what I’ve done so far:

- replaced power filter caps
- replaced all op-amps
- replaced all input/output jacks and isolated them all from the chassis
- replaced every component in the +15v supply for the op-amps
- replaced every component in the bias circuit
- replaced tube sockets with gold-plated ceramics
Dean Vendetta 3 - Dave Mustaine Livewires

Carvin X100B - Bias Mod - Tungsol 12AX7's - JJ KT77's

I have built the most badass 212 that puts all others to shame