RJT> MR> IIRC before the advent of digital synthesized tuners in car radios,
RJT> MR> tuning was done using inductive coils into which a ferrite piston
RJT> MR> would be inserted or extracted, instead of the usual tuning
RJT> MR> capacitor.

RJT>I've only ever seen that in car radios,  myself.

I am thinking the same thing. BUT far back i nthe Fuzzy brain I think I
ran across a Tavble radio that used it. IT woudlc have been only in a
Higher priced model though as it was more expensive to produce.
The reason morotols used it in teir Car Radios is bacuse they came up
with a clever way to change stations with One button. There was a 6 volt
solenoid and a ratcheting mechinism that gave you six positions for hte
Coil slugs.
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 þ SLMR 2.1a þ This note from El Cajon California USA