This is more for the shortwave listeners or ham radio operators using vintage equipment, bit it's still radio related. This is a crystal tester built using a 6AH6 tube, and has a meter to display "crystal activity" and an output jack to feed a radio or counter. It pretty much will test any crystal you throw at it, usually it runs at the crystal's fundamental freq. My father built this back in the day, back in the 50's or 60's.
