Quote Originally Posted by stevo58
Carbon comp resistors (which you’ll have in vintage Fenders) can produce a relatively high level of hiss. Nothing you can do about it.

It is possible to build a tube amp with no audible hiss or hum. I’ve done it more than once. But I used milspec MF resistors, high-quality filter caps, and paid neurotic attention to lead dress.
OP I’ve had to move on tube amps that drove me nuts from their idle hum. Not gain hiss, 50/60hz or pickup buzz, but a low hum whether the guitars were plugged in or not, in different rooms, buildings, speakers, guitars, pickups, leads etc etc. just Hum in the circuit design. Audible when not playing, but humming enough for others in the group to notice. Preamp tubes, tone stack recovery tubes, power tubes, rectifiers all swapped. The only thing I could not try were alternate power supply sections or transformers. I moved them because I have tube amps that do not hum. Ever. One of which is a tweed Harvard. I know it is possible to do right so I still on the lookout. Attention to grounding and lead dressing I believe makes the difference as do the quality of the PS hardware & design. On one occasion it was a tube based pedal amp with a strange behaviour that you could only play clean headroom with gain up at 12 and the class d section down at ‘3’ at most. Weird. The other ( normal to me at least) gave me glorious clean headroom volume if it wasn’t for the damn buzzing when I was ‘sitting out’ during others solos.

if only my tweed could get more volume. It has a 4 ohm 10” speaker that limits its potential.