CMRR from parallel heaters?

[dsavitsk]

Does anyone know if one can supply noisy DC to each end of a heater with a grounded center tap (12au7, etc.) and obtain some level of common mode noise rejection? That is, can one use a DC supply that is noisier than one might use in this sort of arrangement?

 

[Geek]

That's what a traditional hum balance control does.

Hum is induced via h-k leakage. If both sides of the heater leak equally, they cancel each other out.

The CT sometimes works, but is rarely perfectly balanced to leakage currents.

Cheers!

 

[Gordy]

I do not know the actual answer, however I suggest that it would only work (in such as your 12au7 example) if the heaters were physically 100% anti-phase balanced within the unit. The few tubes that I have seen inside have clearly not had that structure, suggesting that you will simply get two dirty paths to ground, and most likely more noise.