This morning I had a brain wave!
The tubes I have in the amp are cruddy ones I had laying around that I put in for the initial test but never took out. So I swapped my power tubes for a set of Groove tubes from my other amp, rectifier with a NOS raytheon 12at7 and my pre-amp with a Telefunken 12ax7 (as well a on the octal pre-amp socket with a NOS sylvania 6SL7WGT) and the squeal went down significantly until I got to higher volume.
When I flick the switch to pull the ground on the tone stack however I get a really bad oscillating squeal as well. The volume jumps a HUGE amount as well so i figure that is part of the problem.
Also I was thinking about the rectifier tube. I have a old 5U4 in there right now, but I have a bunch of nice old NOS 5Y3's and a 5V4 at my disposal. I didn't want to just swap them in though because I couldn't find any definitive cross reference on these tubes. If anyone has ideas on that I would be grateful. As a side note, the voltage across my filter caps seems really low. I am using a recycled power transformer, could this be my problem.
I'm going to change the bias setup right now. I'll be back:)