tube question

There are several pages on the web that give you the prescice data for the tubes tolerances and what you can sub . As mentioned I always do a search on Audio Asylum especially their tube group, first to see if the "pin out" and voltage is very close to the tube I am going to try.

It's not the designation that's so important as long as you use a 5Y3. It's the brand. Different brands of rectifiers (which the 5Y3 is) sound different from each other and affect the sound just as much as different brands in the audio stages.