TESTED WITH ROETEST V10 LONG PLATES. Rebranded Zaerix, they look exact like MULLARD. Tubes NOS/NIB, never used, Tubes and boxes look impeccable. ECC803S is the best option, the highest quality tube available to upgrade from any ECC83 series tubes. Zaerix was the brand name of a company called Z and I Aero Services, an important suppliers to government and military contracts.
They did not make valves themselves but they did source high quality valves from manufacturers around the world and ensured they met their high standards. Tested with Roetest V10, "the Rolls Royce of tube testers" [emissionlab quote], a wonderful german professional system for testing tubes, it shows everything about a tube. We removed tubes close to inferior and superior limits. In photos you can see example of data.
For tubes matched by curves or by Ip and Gm please see our other listings. The tubes passed all quality checks - vacuum, shorts, leakage, heater current etc. The tubes passed all quality tests vacuum, leaks, shorts etc.
, measured with Roetest, curves analyzed. Those who use tubes are more familiar with terms like bias, gain (µ), plate current, slope/transconductance, and maybe someone is wondering what the term "D of plate" in the measured data means. Its value in itself is not so important but it is useful to calculate the other parameters taking into account.S x D x Ri = 1 (slope penetration internal resistance=1), where D is -dUg/dUa at Ia=const. Barkhausen vas a german physicist. He was "the guru" of tubes, his theory and formulas guided the entire period of electronic tubes. If you have any objections please contact me for a specific quotation.