EDIT: I posted some gut pics further below in the thread. Hi everyone, I built my first amp last year, a 5e3 (no kit, just sourced all parts myself), and just looking to get some opinions as to whether this is an actual problem or something I shouldn't worry about. So, with Normal 1 and Bright 2 bridged, and my guitar plugged into Bright 1, both volumes up around 9 or 10, everything sounds great as long as I keep the tone knob under about 5. Once I push the tone past 5 or 6, I get a very high pitched squealing. I'm wondering if this is due to the increased gain of bridging the channels, and therefore something to be expected since I'm using the amp outside of it's designed use? If I do not bridge the channels, there's no squealing whatsoever no matter the volume/tone settings (this works perfectly on both channels). I got out a chopstick and started pushing wires around thinking it might be a lead dress issue. When I moved one of the wires from the phase inverter, the squealing quickly got much quieter and I thought I was on to something, BUT, after some trial and error I found out simply placing my hand in that position had the same effect, even though I was not touching any wires. Just to be clear, I place my hand over the back of the chassis , around the middle, and I'm not touching or contacting anything, just hover my hand in the air, and this really attenuates the squealing a lot. Now, having the tone around 4 is plenty bright enough for me, so I can't see myself trying to play with the settings that cause the squeal, but it just bugs me that there might be some underlying problem in there. I'd love to hear from the members here who are more experienced than I am. Some details: Mostly stock 5e3 circuit following RobRob's layout, but I included his PPIMV mod (deleted Normal #2 input and placed the PPIMV pot there instead, and I used shielded cable grounded on only one end). Standby Switch in the "ground" hole on the chassis. Used a Hammond 1760H OT and have 4,8,16 ohm outputs wired to a DPDT On-On-On switch. I'm using a new EHX 12AY7 in V1, old-but-good RCA 12AX7, old-but-good matched Magnavox 6V6s, and an old RCA 5Y3GT. I have done a lot of tube swapping and the problem persists no matter what tubes I have installed. All voltages test within 10% of typical 5e3 voltage charts I see online Anybody have any ideas or input? Please let me know if I've left out any relevant details. Thanks everyone!