wrote in message
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wrote:
My wife and son are both E.E.'s and their explanation is that IC's
begin to degrade slowly as a result of impurituies in the wafer.
Simple components like capacitors dry out and resistors begin to open
up. Wish I knew more, but I can hear what they tell me in the radios
I've owned. I owned one of the comparison radios, the Panasonic
RF5000b. Big beast of a 24 pound radio with four antennas. It was
pretty insensitive by any measure. Sure it would catch the big
nighttime SW's but that was about it. Other radios, such as a Radio
Shack DX150b were still pretty sensitive (and still raspy sounding)
after 25 years, so the rate of degradation isn't a constant.
I'm not an EE, but I do fix electronics as a hobby. In my experience,
degraded (but not totally dead) ICs or transistors are among the least
likely failures and failed semiconductors are almost always caused by
exposure to excess voltage such as static discharge or funky power supplies,
reversed voltage or drawing excess current through them. Spilled liquids
can be a menace.
Bigger problems are poor solder joints, dried up electrolytics, cracked
circuit boards, drifted carbon composition resistors and home handyman
alignments.
If you're looking for esoteric failure modes, don't forget tin whiskers.
Tin plated conductors, such as the leads on most IC packs, can grow fine
whiskers from the tin plated leads which might short out adjacent pins.
The most likely parts to fail on tube radios are paper capacitors,
electrolytic capacitors and carbon comp resistors. Tubes age as well, but
they're usually OK.
Frank Dresser