best options for a clean 12V DC filament supply for 2 x 12AX7s to retrofit my existing amp

[markr14850]

See last paragraph here:

http://www.valvewizard.co.uk/heater.html

I agree that he makes it clear that only one ground reference should be allowed, either before or after the rectifier. That's most important, else the diodes will give up their magic smoke. However, I think that the schematic he offers (ground reference on the center tap) would introduce buzz, as the potential between the heater and the cathode will be alternating.

[Helmholtz]

. However, I think that the schematic he offers (ground reference on the center tap) would introduce buzz, as the potential between the heater and the cathode will be alternating.

I tend to think that grounding the CT of heater winding takes care of common mode heater voltage.
Reason is that both ends of the heater winding are always connected to the DC output (2 diodes conducting) and that the smoothing cap makes sure there is no difference between the AC to ground potentials of the positive and negative outputs.

I will reconsider if you provide a scope shot showing residual common mode AC voltage.

[markr14850]

I tend to think that grounding the CT of heater winding takes care of common mode heater voltage.
Reason is that both ends of the heater winding are always connected to the DC output (2 diodes conducting) and that the smoothing cap makes sure there is no difference between the AC to ground potentials of the positive and negative outputs.

I will reconsider if you provide a scope shot showing residual common mode AC voltage.

Not a scope trace, but LT Spice...

[markr14850]

Not a scope trace, but LT Spice...

Actually, I re-did the simulation with a CT, grounded, and get essentially no AC reference on the DC. So, not sure what led me to believe what I believed - but now I don't.

[Helmholtz]

Actually, I re-did the simulation with a CT, grounded, and get essentially no AC reference on the DC. So, not sure what led me to believe what I believed - but now I don't.

That's exactly what I was going to suggest. Grounding the CT is essential to balance the common mode voltage.

Nevertheless, thanks for the sims.