"Arny Krueger" said:

Do tell us Arny, about the hum that accompanies vacuum
tubes.

Something about the fact that a lot of tubed equipment doesn't put DC on all
the heaters.

With indirectly heated tubes, there's no need for using DC on the
heaters, except for sensitive stages like a phono preamp.
The hum of my power amps is -80 dB with AC on the heaters.

DHT amps *must* use DC on all heaters, as is the case for over 40
years now.

--
Sander deWaal
Vacuum Audio Consultancy