I'm putting power scaling in this amp next week, so not only will I be able to get phase inverter distortion at bedroom volumes - but power tube distortion too! Power scaling reduces the plate voltage going into the power tubes but maintains the bias current. Apparently power tubes last just as long as preamp tubes when using power scaling! :o
I really need to get hold of a Les Paul and reinstall the extra tube so I can demonstrate some clips of the Caswell mod in this amp...
If you think the amp sounds good right now, you should hear it when I get power scaling in. I've got a grounding issue that I haven't got round to fixing yet, and because the PPIMV renders the NFB loop less effective, extraneous noise gets through the lower you turn it down - that's why the high end in the clip sounds really wierd and unpleasant. I managed to dial most of it out, but you can still hear it if you listen closely. It tends to make the amp sortof sterile sounding. Once I rewire the ground and/or use power scaling, that problem will disappear completely though.