Precision 10-12 "Tube Master" Tube Tester (1947)
This handsome 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 roll charts that tell you how to set
up the tester for hundreds of different tube types.
Stowed in a little compartment in the top you can see a Precision G-140 adapter,
which allowed you to test tube types that were novel at the time: nuvistors, novars, and
Here is the operating manual for the Precision 10-12 and 10-15 testers:
I use this tester once in a while because it can handle older
tubes as well as more recent ones. The next photos show the tester in action,
checking an 807 tube, a five-pin type used in my 1947 DuMont RA-102 television/radio.
If a given tube type doesn't appear in the built-in roll charts, you can look it up
in a separate chart of obsolete and oddball tubes. The following links let you download
PDF versions of both charts, which were compiled by Wayne Hertel:
Precision 10-12 roll chart tube data
Precision 10-12 obsolete tube data
Calibration is the Achilles heel of vintage test equipment,
but this one compares reasonably well against my newer
All tester results must be taken with a grain of salt, of course. It's common for two testers
of the same model to give slightly different results, and certain tube functions, such as oscillation, can't be
accurately evaluated by any tester. I mainly use tube testers to get a basic go/no-go reading. The
best tester of all is a working circuit for which the tube was designed.
If you don't own a tester, or you have a tube type not covered by your tester,
you can make a basic dud/not-dud test by checking the
tube's filament with an ohmmeter. See First
Steps in Restoration for details.
This schematic is provided for any 10-12 owner who needs to
service the tester:
To download it to your computer, right-click on the icon and choose Save Target As.