Rare Philips ECG Sylvania made 7581A power output tubes. These are highly recommended for Dumble type circuits Two-Rock amplifiers, Bludotone, Glaswerks and any other guitar amplifier where you want a super beefy 6L6GC type tube. uprated mil-spec construction these tubes are built to last. Screened and tested, matched for current draw on our Amplitrex AT-1000 and maxi-matcher. Only one piece remaining. NOS in original box.