My 68 Super Bass (converted to superlead specs) squeals when the volume gets to about 7 or so. Here is what I've done to debug, but i think I need some expert advice. The amp squealed when there was NO MV. Changed out PI tube. Still squeal. I put in a MV (Rich-mod) and it still squealed, even when the master was close to 0. That tells me the problem is before the PI coupling caps, not in power stage. It seems to be sensitive to the EQ settings. For example, if I turn up the treble or mids, the squeal comes sooner on the volume dial. That now tells me the problem is post-EQ. I tried moving some of the wires around that are connected to the pots to see if that made a difference. While I was never able to get rid of the squeel, it was obvious that the position of the wires altered when the squeal came on. I'm not sure what this told me, but maybe it says that position of the wires is what is causing it. However, there was no manipulation of the wires that got the squeal to go away. So, it seems the squeal might be one of the following things: arrangement of wires from EQ, the cabs / resistors that form the PI circuit, of the PI coupling caps. HELP!!!