2x TESLA ECC83 / 12AX7. of original 1961-2 TESLA ECC83 tubes. Close date codes: 3/1961 ; 1/1962. One tube has a military 'crossed swords' marking!where a new/unused tube should have around S/gm = 1.60 mA/V, "good" value for transconductance starts at 1.2 mA/V.
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