Matched Pair Ken-Rad 6K6 6K6GT Vacuum Tubes Valves Black Glass 4th Quarter BW52 These four US-made 6SF7 tubes

These four US-made 6SF7 tubes were tested on our Paul Hart-calibrated TV7/U for shorts

They are microphonic and are fine in the preamp stage of my MP-301 and other gentle environments

This pair of GE black plate 6CG7 / 6FQ7 dual triodes was tested on our Paul Hart-calibrated TV7/U for shorts

Delco-BRANDED 6SK7 tested as good on our Paul Hart-calibrated TV7/U

36/37 and 40/38where minimum (65%) is 40/40

Matched Pair Ken-Rad 6K6 6K6GT Vacuum Tubes Valves Black Glass 4th Quarter BW52 These four US-made 6SF7 tubesThis matched pair of Ken Rad black glass 6K6GT tubes was tested on our Maxi Matcher tube tester with 325 volts on the plates and a bias of 36 volts. Tube One drew 20. 4 milliamps' plate current while Tube Two drew 21. 8. Transconductance was 1670 for Tube One and 1570 for Tube Two where new nominal is within one standard deviation of 1900. As I write, I am playing them in my Mini Mite 2013 and they sound great. WE HAVE SCORES OF THOUSANDS OF VACUUM