65 Princeton Reverb Reissue (PRRI) - Hum after heater mod

GoKart Mozart

Aug 30, 2012
Killen, AL
I ran across a couple of Lyle Caldwell's (Psionic Audio) Youtube videos regarding how it's good preventative maintenance to get the high current and heat-generating components off the boards of the Fender Reissue amps in order to prevent damage. Having owned a few older Peavey amps that burned up the factory heater quick connectors, I thought this would be a good idea. I followed along but now I've run into a snag; all tubes are lighting up and guitar signal is passing through the amp, it's just got a REALLY gross hum. Doesn't really sound like either 60 or 120 cycle to me.


Psionic YT vid:

In stock config, the filament secondaries connect to the board at P10/P9 using quick connects. There are two separate wires (WJ12, WJ11) that come from the board that carry the 6.3v to pins 2 & 7 of V6 (the second 6V6); there are also two 100k heater balance resistors (R1, R3) on the board right before wires WJ12 & WJ11 leave the board.


Here's what I did:
1) Snipped off the quick connectors from the filament secondaries, twisted them, and wired them direct to pins 2 & 7 of V6; left the pilot light & filament wires going to the rest of the tubes that were already on pins 2 & 7 of V6. The P10/P9 standoffs are now empty.
2) Removed wires WJ12/WJ11 completely as they are longer needed to carry the 6.3v for the filaments.
3) Wired two new heater balance 100k resistors together with the outside legs connecting directly to pins 2 & 7 of V6.
4) Wired the center lead where the new heater balance resistors are joined to pin 8 of V6. There is a yellow wire already on pin 8 labeled "8(V6)" on the schematic. If I'm reading the schematic correctly, the "8(V6)" yellow wire and the junction of the hum balance resistors both terminate at chassis ground (GND_420V):


Here's a closeup of V6 after the modification; it looks rough right now because I've de-soldered it a couple of times trying to swap around the filament wires to see if that made a difference. Light green twisted wires go to the pilot light, dark green twisted wires are the filament secondaries from the PT, black & white wire twisted together are the filament wires downstream feeding the other tubes, and the two new 100k hum balance resistors are tied together with the outside legs on pins 2 & 7 and common leg tied to pin 8.


Zoomed out:


For comparison, here's a screen cap of V6 from one of the PRRI modification vids from Psionic Audio:


Video of the hum, post mod:

All tubes are lighting up and guitar signal is passing through the amp, it's just got the REALLY gross hum. Appreciate any suggestions on how to run this one down or what I might've missed!
Last edited:

2L man

Friend of Leo's
Nov 23, 2020
I think that mod did not change anything because the pin 8 voltage is only about 0.023V. You should make a two series resistor voltage divider from HV and connect wire there. About +60V elevation is good.

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