Hello good folks of TDPRI who have so lovingly embraced all of my insane questions I use to drop all over FenderForum. I just picked up a 69' Princeton Reverb and I'm slowly tidying up out of. spec resistors and capacitors, replacing the rectifier tube (5U4GB), which has basically melted the PT and other minimally invasive procedures to improve safety and soundness (screen and grid resistors [done]). Basically, if it's on the Rob Robinette suggested mods diagram, I am likely going to do it eventually. Haven't decided on Negative Feedback Loop. Won't be doing Stokes or anything that changes power. Most of the bypass caps have drifted considerably (original Mallory white and blue small). The same is true for the coupling caps (big red dudes) and the bias filter cap. Right now there are two NOS RCA 6V6GT tubes that have likely been assailed by that 5U4GB rectifier for a while along with a mix bag of what appear to be NOS preamp 12AX tubes in V1-V4. For measuring bias, I used the Rob Robinette method to measure my bias. I'm concerned that I'm either doing it incorrectly or something is WAY off with this amp (or my meter). NOS RCA 5Y3GT tube results V5 plate (pin 3) voltage = 424VDC but the measurements kept jumping around 418-416 V5 pin 3 to cathode = -420 VDC V6 plate (pin 3) voltage = 422 VDC but the measurement kept jumping around from 417-415 V6 plat 3 to cathode = -419 VDC OT Voltage Center tap was 428 VDC V5 voltage drop = 8 VDC v6 voltage drop = 9 VDC V5 OT resistance = 151.9 V6 OT resistance = 151.8 V5 measurement: 8 / 151.9 = .052 or 52 milliamps V6 measurement: 9 / 151.8 = .059 or 59 milliamps SMOKING HOT? The amp is also quiet as hell. To get any form of reasonable output I have to dime the volume control. NOS Raytheon 5V4GT tube results V5 plate (pin 3) voltage = 444VDC V5 pin 3 to cathode = -440 VDC V6 plate (pin 3) voltage = 444 VDC V6 plat 3 to cathode = -440 VDC OT Voltage Center tap was 428 VDC V5 voltage drop = 16 VDC v6 voltage drop = 16 VDC V5 OT resistance = 151.9 V6 OT resistance = 151.8 V5 measurement: 16 / 151.9 = .105 or 105 milliamps V6 measurement: 16 / 151.8 = .105 or 105 milliamps SMOKING HOT? The amp is quiet but not as quiet as the 5Y3GT. It sounds better overall. It's been about 10 years since I've had my probs and meters inside a chassis so I am coming back up to speed and I hope I am heading in the right direction. I'm looking forward to your assistance in gut checking me. I have a GZ34 heading toward me that I am also going to try in there.