Matched Pair National Union NU Number / Type 76 #76 Vacuum Tubes Valves 7AH7 Sylvania

Matched Pair National Union NU Number / Type 76 #76 Vacuum Tubes Valves 7AH7 SylvaniaThis matched pair of National Union type 76 triodes was tested on our Paul Hart calibrated TV7 U for shorts, gas and transconductance. There were no shorts or gas. Transconductance measured 49 for Tube One and 52 for Tube Two where minimum (65%) is 36 and 100% is 55. These tubes have shiny, dark gray, rounded plates; crenelated, top, rectangular mica and smooth rectangular bottom spacers and excellent flashing. I have played them in my Radio Craftsmen

gas and transconductance

6 milliamps

but most should work in most circuits

Source material is The Beatles "Yellow Submarine Songbook" and they sound terrific

This new old stock-testing lot of six Tung-Sol black glass 6K6GT tubes were tested on our Maxi Matcher 2 with 325 volts on the plates and a bias of --36 volts for shorts

Transconductance was 1900 for Tube One and 1800 for Tube Two where new/nominal is within one standard deviation of 1900

new in box Sylvania 25Z5 tubes tested to spec on our Paul Hart-calibrated TV7/U

They measured (from left to right) 27/26

noise or gas and it tested as follows:

These three 6G6G tubes were tested on our Paul Hart-calibrated TV7 for shorts gas and transconductance

I am playing them in my Sound Craftsmen RC-2 monoblocks at 6

new in box 6SR7 tubes tested to spec on our Paul Hart-calibrated TV7/U