[Bloody Sam Roberts]

Even before Radio Shack about every hardware store had a tester and tubes.

For certain musicians and audiophiles, those things go for big bux. They use tubes in their amplifiers and are constantly on the look out for NOS (New Old Stock) tubes and reliable testers.

[nascarnation]

“The same sort of vacuum tubes that make a Stratocaster sound the way it does through a Fender Twin Reverb amplifier worked to automatically drop the high beams until the approaching car passed.”
https://www.hagerty.com/media/archived/photonic-technology/

I know a guy here in Indiana who repairs/rebuilds these for old Caddys and Buicks.

[Openurmind]

Sure are!