Matched Pair RCA Black Plate 6AU7 Vacuum Tubes NOS-Testing

Matched Pair RCA Black Plate 6AU7 Vacuum Tubes NOS-TestingThis new old stock testing, perfectly matched pair of RCA black plate 6AU7 dual triodes was tested on our Hickok 800 for shorts, gas and transconductance. There were no shorts or gas. Transconductance measured 2600 2600 micromhos for both tubes. (New 6AU7s typically test within a standard deviation of 2400 micromhos). I am playing them in my Alan Eaton single ended triode amplifier (with adapters, not included) as I write and they sound great. These

(New 6679s typically test within 1

1 milliamps where new 6L6GCs typically test with plate current from the low 20s to mid 30s and transconductance from 2200 micromhos or so

These four US-made belll-plate number / type 77 tubes were tested on our Paul Hart-calibrated TV7/U for shorts

new in box CBS-Hytron 12BZ7 tube tested to spec on our TV7/U

They sound great in my Alan Eaton single-ended 45 amplifier (with an adapter

This pressing has light surface noise audible only in quiet passages

It drew 27

These eight Philco 7B8 tubes tested as follows on our Paul Hart-calibrated TV7/U where minimum (65%) is 29 and 100% is 45:

34 and 35 where striking range is between 30 and 40

These nine new old stock

Transconductance measured 1950 micromhos for both

new in box Sylvania 14A7 / 12B7 tubes in this lot