In article ,
Ron Hardin wrote:

One problem with rectifiers is that they ground and unground the
RF path 120 times a second (60 Hz) and unless bypassed will add a hum
to a received station that has nothing to do with ripple. Many supplies
have this fault.

Snip

Wrong theory on the hum but the right solution. I've giver the reason
for this a number of times and I'm not doing it again. Anyone that has
build linear and switching power supplies knows the reason.

--
Telamon
Ventura, California