PY 81 as power rectifiers?

[Amie]

Hum cancelling....So...What if anything, went wrong ?:

https://www.radiomuseum.org/forum/grundi...guage_id=4

Lawrence.

Thanks for that link Lawrence, in the first instance the little Grundig sets audio output stage reminded me that I had read Bernhardt Kainkas article (http://www.b-kainka.de/roehren/gegentakt.htm ) on self split and balanced class A circuits, that allowed the use of interleaved mains transformers.

Nothing really went wrong, I was trying to balance out the standing current in the mains transformer, to stop saturation, that worked OK, then I tried a half wave rectified supply rather than the bench PS to deliberately introduce ripple to test the hum cancelation theory, and that worked too, but not at the same "balance" setting. 

When I tried a proper gapped transformer, that had been kindly donated  the circuit was improved regards efficiency, and  sound quality.

With the mains transformer I used with its equal windings the current in the balance side had to be around 25% (4mA) of the anode current for it to work, not what I was expecting. The hum cancelation needed only about 500uA, increasing above that made the hum worse....

As others have said, the ratios of the windings have to be in proportion to the ripple on the supply AND the respective currents.... It work well if you get it right, but, makes things worse if you get it wrong. Also I don't think both effects could be reconciled without resorting to push pull output....

Or at least I'm not clever enough to do it

Amie.