tony sayer wrote:
which leads you
to directly heated triodes, then you have to consider the fillament
supply, DC hums less, but AC sounds better.


Do they still make directly heated valves and surely AC would hum like
no ones bizz, or was this some wind up?....

Yes, it can do depends on design, no it wasn't

For eample of current production...

http://www.westernelectric.com/300B/specs300Bindex.html

--
Nick