This has me stumped... I built an amp inspired by SLO: https://www.tdpri.com/threads/slo-inspired.1057751/ The amp works fine. I recently hooked up the tube driven FX loop and I was taking voltages to determine if I was going to change any power supply dropping resistors when I noticed a huge differences in the V2 voltages depending on if the channel was engaged or not. This is with volume and master volumes at zero. Specifically: see preamp schematic below. S3 is the OD channel switch and it services both ends of V2. For instance, the V2A plate pin 1 voltage reading is 235V with the OD channel engaged and 180V with the OD channel switched out. Any idea how and why that would happen? Up to now I never payed any attention to what channel was engaged when taking idle voltage readings. I am stumped!!!