I added an adjustable bias, which I think this amp desperately needs, and I also copied Fred's amp's cathode bypass cap scheme: The standard 25 µF cap is changed to 4 µF, and paralleled with a 1 µF Tantalum capacitor. This is a gimmick used by Hi-Fi guys to improve the frequency response of the stage - basically the Tantalum cap is "fast", compared to the "slow" aluminum cap, and can take over when the "slow" cap bogs down due to its time constant.
You can see the adjustable bias pot on the bias supply board. You can't see the Tantalum/Aluminum parallel caps, because they are inside the Astron Minimite shells.
You can read about the PR tremolo Peculiarity on my blog, here:
I love Fred Shuman's 1967 Fender Princeton Reverb. The tone from this little amp is to die for. I suspect that the incredible tone is due to a combination of things, probably not the least of which is the PR's Cathode Follower Phase Inverter circuit design.
I built this amplifier around the rare and highly desirable 1966 Jensen C10PS, the "S" standing for "Special". As far I can tell from the research I have done, there is no real consensus on what "Special" means, although it seems to be a larger magnet/voice coil. The Speaker was only available in the Princeton Reverb in 1966 and 1967, and was rare - most PRs had the Jensen C10P.
I made reproduction capacitors, both blue tubulars and Astron Minimite electrolytics, so the circuit looks like it did in 1966.