In article ,
Michael A. Terrell wrote:
Delco used a very thin double sided PC board at the input as a "Spark
plate", followed by a large filter choke. Anything over the voltage
rating of the gap arced over from the input lead, directly to the
radio's case.

And this was used to protect against voltages of 50 or so? I really can't
see that being a reliable method in the hostile environment of a car.

BTW, the first transistor car radio I had was a hybrid kit where only the
AF was handled by transistors. Early '60s. No sign of anything like that
on it. Perhaps Lucas electrics couldn't produce much over 14 volts. ;-)

--
*On the other hand, you have different fingers*

Dave Plowman London SW
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