PY 81 as power rectifiers?

[Amie]

Keeping the heater supply separate from the HT is a good idea. At 50mA HT there should be no problems with halfwave. Do you know what sort of resevoir cap you'll use? Or alternatively how much ripple you can tolerate. To a fair approximation CV=It. C is the cap, V is the ripple voltage, I is the DC current and t is the cycle period. 20ms for fullwave, 40ms for halfwave.

For 50uF and 50mA that's about 40V of ripple unless I've made a magnitude error. For most purposes you'll need a smoother cap with resistor or choke to get that down to something respectable.

Bear with me here,

One idea (not mine), I have some 6w mains transformers that when loaded with a 16 ohm speaker will give a not to bad a match for the pentode section of a PCL 83 or similar, across half the primary.

So, what I intended trying is to feed the rectified HT via a 47uF (reservoir) cap to the center of the two primary windings in series, one primary to go to the anode of the output pentode, the other to power the rest of the set via another 47uF (smoothing) capacitor.

Why? Well if you look at the output stage of the Grundig 80U that I repaired, it uses a similar system. Now I thought it was a way to provide the rest of the set with nice flat DC without the expensive choke. But, the transformer in that set is very small, and the core is interleaved, not gapped, (I Think that it's original), why Grundig did it that way I think is to balance the standing SE current in the output valve with the current in the rest of the set, (I measured it, they're similar), by that means they were able to use a smaller component for the transformer, AND, provide "lossless" smoothing.

If I'm right, then that's a pretty cool piece of design work.

I can't fathom how well that idea will work with the random parts I have to hand, but it may be fun to cut and try.

If anyone has any insights, then please chime in.

Thanks ,
Amie.