Multiple filament windings and virtual center tap(s)

[lord preset]

I am using an Antek toroidal PT with two non-center tapped 6.3v 3A windings. I plan to use one for the power tubes and one for the preamp tubes. I read elsewhere that an artificial center tap wasn't really necessary/useful for power tubes. Does that sound true? Or will I need to plan for two artificial center taps?

[pdf64]

I suspect that any benefit from a balanced 0V reference on the power tube heaters may be negligible, especially if both heaters are wired in the same polarity, so as to cancel out any hum introduced to the cathodes.
It should have a 0V reference / connection to one of the legs though.
On the other hand, an artificial CT is only 2 resistors, and even a negligible benefit is still a benefit.

[catalin gramada]

Hi
That's the best way I found to keep the filament noise to absolutely none: sparate heater windings: one for PI & power tubes and one for the rest of preamp circuit. You need a dc reference for both 2 x 100 ohm resistors for each section and separate leads from each mid junction to main star. Don't bother with balance pot aka humdinger it not do any diference in this case. It's absolut quiet. Cheers

[tubeswell]

I suspect that any benefit from a balanced 0V reference on the power tube heaters may be negligible, especially if both heaters are wired in the same polarity, so as to cancel out any hum introduced to the cathodes...

Just pondering this.

A centre-tap (or artificial centre-tap) on the winding ensures that both sides of the winding will see equal voltage swings on either side of a neutral reference point.

If you don't have this neutral reference point in your P-P amp, then won't one side of the OT primary see a higher VAC ripple than the other side (in terms of what might be riding on the output stage signal)?

[catalin gramada]

Just pondering this.

A centre-tap (or artificial centre-tap) on the winding ensures that both sides of the winding will see equal voltage swings on either side of a neutral reference point.

If you don't have this neutral reference point in your P-P amp, then won't one side of the OT primary see a higher VAC ripple than the other side (in terms of what might be riding on the output stage signal)?

Actually there are a lot of circuits which used just one side of power stage heater winding to ground for reference. of course will ride the ac ripple on output stage but even so snr it was considered good enough in this point. pretty simple to improve it, two resistors cost almost nothing

[tubeswell]

Actually there are a lot of circuits which used just one side of power stage heater winding to ground for reference. ...

true