Precision 10-12 "Tube Master" Tube Tester

This impressive Precision Model 10-12 "Tube Master" tube tester looks like new and works like it, too.

I bought it for $10 from a guy whose basement was crammed with tubes—thousands and thousands of tubes. Somewhere in his travels he had come across this tester, which he didn't want at the moment. He obviously didn't need it, either. Also stored in the basement were a couple of dozen other testers.

Housed in a blonde wooden cabinet, this tester has enough knobs, switches, buttons, levers and sockets to put Dr. Frankenstein on Cloud Nine. Visible through windows on the bottom are the paper rolls that tell you how to set up the tester for hundreds of tube types.

I use this tester once in a while because it can handle older tubes as well as more recent ones. At the top of the photo you can see an adapter which allows you to test additional types that were new at the time.

Calibration is the Achilles heel of vintage test equipment, but this one compares reasonably well against my newer Sencore tester.

All tester readings must be taken with a grain of salt, of course, particularly when the tester's as old as this one. There are some tube functions, such as oscillation, that no tester can evaluate accurately, and it's common for two testers of exactly the same model to give somewhat different results. I use testers to get a basic go/no-go reading on a tube. By far the best test of a tube is in a working circuit for which it was designed.

The schematic is included for any 10-12 owner who needs to service the tester.