This matched pair of RCA black plate 6SN7GTB dual triodes was tested on our Paul Hart-calibrated TV7/U for shorts, gas and transconductance. There were no shorts or gas.
Tube One measured 66/72while Tube Two measured 66/77 where minimum (65%) is 50/50.
These tubes have black plates; smooth, rectangular mica spacers; steel support rods; standard, side-D getters; short bases and LA and KJ date codes, respectively.
I am playing them now in my Radio Craftsman RC-2 mono blocks with Pink Floyd's "Obscured By Clouds" and they sound terrific. They are dead quiet when the preamp is muted and have excellent frequency response, sound-staging, and dynamics.
R.