The Hoffman AA964 schematic looks like an earlier version "I-FD" near the top instead of "L-FD". Also, the FFG/Ampwares schematic says "A division of Columbia Records Distribution Corp", not just "Fender Electrical Instrument Company". Although the transformer part numbers are the same, the earlier version shows 325 VAC on the PT secondary instead of 340.
The really odd thing about the earlier one is that it includes the same shape symbols for the Mallory cap can as the later schematic (and shape symbols actually on the cap can of the PR on my bench right now). However, it looks like two sections of the cap can are tied together for a 40uf reservoir cap (plate node) in the earlier amp. The PI and preamp voltages of the earlier version are higher because of the "missing" 18K/20uf node on the power rail which is un-used in the later schematic. (Un-used in the sense of not being connected to anything. It adds filtering for the PI and preamp and drops voltages.)
My guess is that the earlier version has more clean headroom and more bass response with the 40uf filter on the plate node, but that's just a guess. It probably sounds different when pushed into overdrive. IOW maybe not as nice an overdrive sound - don't know though.
It's also interesting that the Princeton Reverb AA1164 schematics look like the later one with 340 VAC on the PT secondaries and 420 VDC coming off the rectifier. However, the AA1164 screen, PI & preamp voltages are all a bit lower. Must be due to current draw of the reverb section of the circuit. Also, the FFG shows an AA1164 schematic which shows the same PT voltages & power rail layout as your later AA964 - but with a 5U4GB rectifier:
http://www.thevintagesound.com/ffg/schem/princeton_reverb_aa1164_schem.gifThe "Stokes" mod on Princeton Reverbs is to connect the PI to the "un-used" filter node on the power rail, raising the plate & cathode voltages of the concertina splitter. The goal is to raise the clean headroom in the PI. Some weird things do happen in that PI when pushed into distortion. Look at
THIS THREAD for a recent discussion.
You might want to try moving the splitter's plate supply to the power rail node between the two 18K resistors just to listen for an overdrive difference.
Weak tremolo might be a leaky cathode bypass cap on the tremolo triode. Also, the power tube bias has a big effect on how much tremolo you hear. Too hot, and you can't hear the tremolo as well. Too cold and it sounds like crap (to use a technical term
).
Don't know if that answered your question at all...
Chip
Topic: Princeton Amp - AA964: Two schematics! (Read 7286 times)