When in doubt, use 33uF or so, @450V (22uF is OK for a start. If the
hum reduces but does not go away altogether, then go up). Otherwise,
200uF @20V or so for LV stuff.

Bridge: Voltage in X 1.4142 = voltage out.
Single diode: Voltage in .7071 = voltage out.

Keep that in mind.

Peter Wieck
Wyncote, PA