[maxhifi]

As per title... the ever popular AA5 power supply has a half wave rectifier, and a small input filter cap. The result is audible hum, under all circumstances.

Can't increase value of the filter cap without exceeding the peak current capability of the 35W4, and shortening its life. Good thing about a half wave rectifier though, is the ripple frequency is 60Hz, which is well below what the output transformer and speaker of a typical AA5 are capable of reproducing. During the day, this is no problem, but for night time listening at very low levels, there's residual hum audible in all of my radios.

A long time ago, I made a massive DC power supply, using four 6AX4 TV damper diodes in parallel, into a 1500uf capacitor. Plug the AA5 into DC, and the hum is gone - it's very cool. But now the 50C5 isn't getting the voltage it needs for full output power. Probably not a big deal.

In a few old designs I've seen ripple voltage added in reverse phase to the input of an audio amp, at just the right amplitude to achieve hum cancellation. I'm thinking this may be the easiest strategy to try. This how my RCA theatre amplifiers get away with having only a 14uF filter capacitor and inaudible him, but it requires periodic adjustment.

Aside from the two ideas above, or using a hum bucking winding on the output transformer, is anyone aware of any clever hum mitigating circuits from days gone by? I have a little silvertone clock radio by my bed which I listen to ever night, and due to the clock it can't be used on DC.