Question About Capacitor Upgrade in Tube Amp

Capacitors have their own technology, dynamics and very often audible characyeristics. Anybody who disagree most likely never replaced one in the audio path of their high-quality equipment piece.

As for capacitor used to shunt DC power supply, they are necessary to eliminate high-frequency noise present there, but never affect the sound quality as much as a different coupling (serial) capacitor used in the audio path.

I'm also a strong believer in using high quality film caps. I've had good luck with V-cap ODAMs (very neutral and clear) and Miflex KPCU (a bit warmer with a beautiful midrange tone). 

A couple things to keep in mind. These caps all take a few hundred hours of break-in to sound their best. And some will actually sound worse during the break-in period. 

And most important, these amps have LETHAL voltages inside. Capacitors can hold a lethal charge for a long time. Make sure you are thoroughly familiar with the safety procedures before playing around inside a tube amp. The OP mentioned doing DIY guitar amps so is probably already familiar, but anyone else contemplating doing this kind of upgrade should use extreme caution. 

As for capacitor used to shunt DC power supply, they are necessary to eliminate high-frequency noise present there, but never affect the sound quality as much as a different coupling (serial) capacitor used in the audio path.

@eworkflow Are you an engineer? Do you have a test lab? Verified the bypass capacitor values actually sink just the noise and haven't changed the DUT frequency / phase response?

'Noise' is not a constant and changing capacitor value / type may actually make things worse.

Changing type / value changes the power supply impedance and phase. Whether or not it is an improvement may be dependent on the DUT, the rest of the system AND the CBLF*.

Making willy-nilly recommendations is irresponsible.

*: the listener with all its inconsistencies.

@ieales I don’t know what social setting you acquired your accusatory tone from, but your ridiculous accusations of me being irresponsible have no merit. First, I wouldn’t suggest changing it to anything different nor ever stating that capacitors do not affect sound in the audio path. So, in short, I am "irresponsible" for saying that the primary role of low-capacitance capacitor shunting DC power supply is to filter HF noise. Secondly, please present a literature source to confirm your "power supply impedance and phase" being audibly affected by a low-capacitance shunt capacitor or just shut up. I am well aware of the fact that power supply quality will affect sound, but you are taking your holier-than-thou mission too far.

@eworkflow 

Agreed. 
Completely unnecessary obnoxious and immature forum behavior.

Charles