TWO Amperex 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Tubes test at 10770 and 10600 where 6630 micromhos is pass/fail grade. +100% gm test results / matched within 2%.
ONE RCA 7591A vacuum tube. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). CE date code = October 1968. +100% plate current test results. Tube 1: 11520 micromhos @ 76.2mA plate current emissions.
TWO Amperex 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Matched 78-13 date codes = 1978 week 13. Tubes test at 10800 and 10940 where 6630 micromhos is pass/fail grade.
TWO The Fisher 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Tubes test at 6950 and 8070 where 6630 micromhos is pass/fail grade. This is not great matched pair, but two good singles.