TWO Amperex 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Tubes test at 9550 and 9800 where 6630 micromhos is pass/fail grade. No rattle / tight base / no loose parts.
TWO Amperex 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Tubes test at 10010 and 10350 where 6630 micromhos is pass/fail grade. Gm matched to within 3.5% difference. No rattle / tight base / no loose parts.
This tester also is used in conjunction with a variac to maintain test results accuracy and consistency. This tube tested at- 68. Average new tube value - 56. I will always list original photos of actual item you are receiving.
TWO Amperex 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). Tubes test at 11650 and 9690 where 6630 micromhos is pass/fail grade. 133% / 101.6% mA plate current. 114.2% / 95% gm mutual conductance.
TWO McIntosh 7591A vacuum tubes. Tested on Amplitrex AT-1000 tube tester (fixed bias mode). 85.6% / 86.8% gm mutual conductance. Tubes test at 8740 and 8860 where 6630 micromhos is pass/fail grade. Tube 1: 8740 micromhos @ 60.6mA plate current emissions.