[AMC-List] stuff gets old!

[Tom Jennings <tomj@xxxxxxx>]

The AM radio in my 63 Rambler Classic died this past year. I
actually listen to AM in that car. The service manual for
this radio is excellent (though the radio itslef is el cheapo)
and I've got the tools so I went at it.

The final straw was -- silence. It just shut up. The final audio
transistor, the antiquated but long-lived 2N174, died. The
circuit used is crazy, they run the damned thing about 150
degrees, that one transistor consumes more power than the 10
million transistors in my laptop, it's surprising they last at
all, never mind 40 years! (And that laptop will last... ?)

2N174 has long since gone obsolete. $15 on eBay when you see
them. Found a couple at a local surplus store for $1. That
problem is solved.


It had developed a weird tuning problem a year or two ago, where
sometimes a station would get "wide" in the dial; rather than
requiring fine tuning, your could turn the knob two or three
turns and barely leave the station behind. But only sometimes.

Oddly, it did it on local trips in LA, but not much on long
trips, like 800 miles to Santa Fe.

I found the problem only with luck: the radio tunes stations
by mechanically pulling little powdered-iron slugs in and out
of coils inside the tuner. If you've ever taken a car radio
apart you've probably seen the arrangement, pretty much every
car radio ever made uses it (because it's immune to vibration).

The slugs have a long threaded neck for adjustment. It threads
into a plastic plug in the tuning bar that goes up and down.

There is a #1850 or something lamp that lives behind the dial,
to illuminate it. When tuned to 1050 AM or so, the lamp sits
right behind the center tuning slug's plastic plug.

Motorola wasn't stupid; the lamp can't melt the plug. But it
speeded up decomposition of the plug, and lo, 40 years later,
it disintegrated into goo and only gripped the threaded rod
of the tuning plunger when (1) not tuned near 1000 and (2)
the temperature situation was right (wrong).

Never would have found it if I was testing in Arizona. There,
I listen to KTNN (Navajo Nation News) which is around
500-something. In LA listening 1050 causes the goo to soften.


So why is it we drive these old things?!

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