This lot of three Sylvania tall base, coated glass 50L6GT tubes was tested on our Paul Hart-calibrated TV7/U for shorts, gas and transconductance. There were no shorts or gas.
They measured 59, 72 and 76 where minimum (65%) is 45.
This new old stock, new in box matched pair of GE 6FQ7 / 6CG7 dual triodes was tested on our Paul Hart-calibrated TV7/U for shorts, gas and transconductance. There were no shorts or gas.
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Tube One measured 80/80 while Tube Two measured 82/84 where minimum (65%) is 50/50 and 100% is 77/77.
These tubes have copper support rods; top O getters, gray ladder plates; excellent flashing and three horizontal holes underneath and parallel to the plates' short axes.
I have played them in my Sound Craftsmen RC-2 monoblock amplifiers with adapters (not included) and they sounded outstanding. They were dead quiet when the preamp was muted and had excellent frequency response, sound-staging, and dynamics.