Question About Capacitor Upgrade in Tube Amp

@ieales   Absolutely. Total agreement here. LC - LC forever!

In a break-out box, I have compared V-caps with Solen teflon f&f  and Relcap teflon f&f. The latter are good and quite similar IMO, and the V-caps are bright. To my ears, in my system, in my comparison. YMMV.

And for really low values, less than a couple of ohms, nichrome wire just can't be beat.

ANY cap upgrade is useful, power supplies included.

In general, the type of capacitor is more important than brand. From cheapest (and least good) to best: metallized insulator, film and foil, air gap, vacuum. There is a good discussion of this in 'Art of Electronics.

Next most important are the materials: polypropylene, styrene, teflon (insulators); aluminum, tin, copper, silver (conductors).

Polypropylene is not as clear, teflon can be a little harsh. To my ears, styrene is just right. Conductors are not as important, although there are differences. Aluminum is prone to corrosion and can be a little harsh. Copper is expensive. I find tin to be a good compromise.

I mainly use air gap and vacuum caps for the most important components, such as RIAA compensation. For amps, I usually use styrene.

For brand, I use MIT or Relcap for signal path, Solen for power supply. Phono stage uses Solen teflon for the final power supply filter. Good luck!

YMMV

Resistors make a difference too. I tested half a dozen candidates with a rotary switch in my preamp. Nude Vishay resistors were the best, no-name metal films from Taiwan second, aerospace hyper-expensive last.

You ask, "Does anyone know how the power supply bypass capacitor effects high end frequency response?"

Maybe. The component may sound smoother, with a less etched treble if the power is cleaned up with such a capacitor. This etched treble is distortion which has been removed. Some who are used to digital may not like the effect.

I would also suggest that Dielectric Absorption (DA) is the most important measure for modding, because the other measures should have been considered in the design phase. The properties you list are critical when using electrolytics, which are not (should not) be under consideration here.

@ieales

Agreed that those properties have not been mentioned. But which of them do you consider more important than DA? You seem to have left that thought unfinished.

You say, "OH, yes they should." But my reading of the OP is that the question concerns coupling and bypass caps. Are you seriously suggesting bypassing with electrolytics?

Of course modern electrolytics are better, but that is not the question as I read it.