2x TESLA ECC803S (CV4004 7025) Long Plate lk Siemens E83CC 1960 Prototype Series
2x TESLA ECC803S (CV4004 7025 ~5751), 4/1960+8/1960 Prototype Series, 100%/Matched, 123+126.where a new/unused tube should have S/gm = ~1.60 mA/V, good value for transconductance starts at 1.2 mA/V.