"Peter"

Yes, all agreed, and of course the reason that the early stages *do* have
to
have a smooth anode supply is that they are single ended, unlike the
output
stage.

Arfa

Yes that is part of it, as well as the fact that there is
amplification of the early stage hum.


** Yep - that is why there are several stages of filtering between the
raw DC ( at the first filter electro ) and the input triode.

Having a choke ( ie inductor) after the first electro does amazing job
reducing ripple by a factor of a hundred or more with no loss of DC voltage.
Then two or more resistor & electro stages are used.

The supply to the input triode need to have less than 50uV of 100Hz ripple
to ensure no audible hum.

Makes the overall ripple reduction in the order of 100,000 to 1.



..... Phil