Good memory Cab!

It is likely that 1964 Plymouth radio still has psome Tubes inside.

from

https://www.caranddriver.com/features/a15128476/the-history-of-car-radios/

1963: First All-Transistor Radio

A number of manufacturers introduced transistors to their aftermarket car radios in the early 1960s,
but (German manufacturer) Becker’s Monte Carlo model was the first to be fully “solid state”—no vacuum tubes.

I guess that also means finding an antique radio repair shop, and the chance that replacement tubes may not be available.

but Wikipedia says:

In April 1955, the Chrysler Corporation announced that it was offering a Mopar model 914HR branded Philco all transistor car radio,[11] as a $150 option for its 1956 Chrysler and Imperial car models. Chrysler Corporation had decided to discontinue its all transistor car radio option at the end of 1956, due to it being too expensive, and replaced it with a cheaper hybrid (transistors and low voltage vacuum tubes) car radio for its new 1957 car models.[12]
In 1963, Becker introduced the Monte Carlo, a tubeless solid state radio with no vacuum tubes.[10]

https://en.wikipedia.org/wiki/Vehicle_audio