Putting vintage tubes in the power supply of pre

Some of the greatest sonic benefits in this hobby are achieved via power supply mods. ie: (http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1238465914&read&keyw&zzmullard+5ar4) That refers to the improvements in a power amp, in which the output stage's gain is realized as current(read the post following his rectifier replacement). Your pre's gain stages are all voltage, but the voltage that's modulated(YES- that IS the correct word) by the signal, and conveyed to the next stage, all comes from the wall outlet, via the power supply. The tubes you choose to use in your PS can have a dramatic effect on your presentation.

Power supply tubes do not affect the sound IMO

May I ask on how you formed this opinion?

The voltage in the power supply is what makes the "sound" that you hear, technically speaking. Any change there affects everything because it dictates how the circuit operates.

What am I missing?

Dan001,

If you disclose the brand and model of your preamp, someone at Audiogon may have direct experience or at least can look up the circuit and tubes used and make an educated guess.