Preamp nasty noise and hum

[hpeter]

fyi
output measured with grounded/floating filaments

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

yours 15khz is interesting

 

[TonyTecson]

lifting the heaters to positive or negative bias after floating helps all the time ime....

 

[MelB]

When I build an amp first thing I wire are the heaters. TIGHTLY twist the wires and run the twists as close as you can to the sockets and lay the wires right against the metal chassis.
Yes even if you have DC to the filaments.