Sylvania Brown Base 6SL7 WGT Audio Tube.

Tested STRONG at 120/120 min 55/55.

Tested on a recently calibrated B&K 747 Dyna Jet Tester.

1940, 40s, 1950, 50s, 1960, 60s, 1970, 70s. Tube(s) shown in pictures will be the exact tube(s) you will receive.