Charles Hawtrey wrote:
"author" pondered the futility of human existence in
an uncaring universe and yet found the courage to write:


The radio in question is a Radio Shack DX66 from around 1986.
It does not have the hum when operating on battery power.


Bingo, the AC supply.

I don't know anything about the radio in question. Does it use the
typical "wall wart" power supply? These often are poorly regulated so
it's not surprising if you get a hum when using it.

If you are using a wall wart there are various things you can do to
reduce hum. The simplest is to try connecting a Great Big Honking
Capacitor (tm) across the leads (being careful to observe proper
polarity). If the AC to DC conversion is internal to the radio,
things get a little more complicated.


--
hambu n hambu hodo

Besides AC hum from a poorly filtered power supply, an AC adapter can
bring in RFI from various noisy gizmos around the house - this is solved
by putting a ferrite bead on the power lead.