Filament DC offset for hum

[Chuck H]

Suppressing hum by doing [whatever] to heaters only works to the extent that the heaters were where the hum was coming from.

I had a Norton 850 Commando once. No matter what I did to the heaters, the mufflers were where the noise came from.

Is there a secondary joke hiding in this post or did that bike actually have a heater of some kind???

[Chuck H]

A little off topic and just thinking out loud now...

Regarding elevated heaters: If the filament is biased positive WRT the cathode why doesn't it act like a plate? Where electrons are drawn to the filament. Is there any reduction in voltage gain efficiency by positive biasing the filaments?

[Enzo]

Um, the question was 120Hz hum. That comes from power supply ripple and associated ground currents. Elevating heaters or not will have no effect. heater related hum will be 60Hz. If you rearranged some grounds, it was probably that rather than heater elevation per se.

[trobbins]

The link collates details relating to hum in valve amps, including how elevation changes heater-cathode resistance. It may be of assistance.

http://dalmura.com.au/projects/Hum%20article.pdf

[catalin gramada]

The link collates details relating to hum in valve amps, including how elevation changes heater-cathode resistance. It may be of assistance.

http://dalmura.com.au/projects/Hum%20article.pdf

Great article.Thanks for You work

[dcoyle]

Thank you very much for sharing that paper.

Dan

[trem]

Yes, Thanks for that.....looks very good (to me).
You have increased my reading back-log by another day.....so it is now up to 10 Years, plus one day.