Heathkit model TT-1 Gm tube tester.

excellent condition

comes with documentation.

I did test this machine by placing a 6L6 tube in the tester with a known Gm.

my calculations show this tester is within 6.6 percent of the correct reading.

It is a very nice laboratory grade tester 

Please note a scratch on the left side of the meter face.

Thanks for looking