PY 81 as power rectifiers?

[ppppenguin]

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.