Power supply upgrades

I'm not familiar with the Nichicon electrolytics, but assuming they are of at least decent quality I don't think you'll gain anything by replacing them. You might realize some small benefits by paralleling ("bypassing") them with good quality film caps, of lower value, although I agree with Elizabeth that capacitors in the signal path are much more critical.

Electrolytics provide filtering of ac ripple, and energy storage. They almost invariably provide poor performance at high frequencies, so bypassing them with a polypropylene or other good film capacitor will potentially help filter out noise or other garbage before it reaches the components that are in the signal path (where power supply decoupling/bypass capacitors are presumably incorporated as well, but cleaning up the dc voltages as much as possible before they enter those areas can't hurt and might help).

The capacitance values you listed for the electrolytics strike me as adequate for the relatively low and fairly constant current draw of a 3 x 12AX7 phono stage, so I don't think there is anything to be gained by increasing their values. Adding the film bypass capacitors will, of course, provide a bit of added capacitance as an incidental benefit.

Regards,
-- Al

What value bypass caps should those electrolytics be bypassed with?

I don't think it's particularly critical, as long as the bypass caps are of good quality. Anything from 0.1 to several uf strikes me as reasonable. If you find indications of particular values that worked well for people, in the forums you spoke of, go with those, but quality is probably more important than value.

Rodman -- As I think you indicated towards the end of your post, I'm not sure that the improvements you cited, which were mostly with power amps, would be relevant to a phono stage's power supply, where the current load is much more stable as well as much lower.

Regards,
-- Al

What do you think about the 160v rating on 22uf caps, enough?

I don't know what voltage the power supply is outputting to the plate circuits of the 12AX7's, but I suspect you should go with a considerably higher rating on the caps than 160V. Perhaps the 12AX7's are being run somewhat lower than 160, but probably not much if anything below 120 or 130V. And the 12AX7 and 12AX7A have rated plate voltage maximum's of 330V, so in the absence of further information it could very well be that they are even being run a bit above 160V.

Good derating practice in my experience as an electronics design engineer (although it was in defense avionics, not audio!) was considered to be a factor of 2 or more. Meaning use capacitors with voltage ratings of 2 or more times the actual voltages that are likely to be encountered; otherwise long-term reliability is degraded.

And, finally, the 450V rating of the existing electrolytics was probably chosen for a reason!

Regards,
-- Al