From a Vacuum Tube Valley Bendix Shootout:
The base is some kind of ceramic material. The construction is luxurious with all-ceramic spacers and a heater block. The pinout is the same as the obscure Tung-Sol 6AR6, a very similar tube to the 5881 physically but not quite the same electrically. Still, the 6AR6 or 6384 can be easily substituted into a 6L6 socket with rewiring or an adapter, and are rated closely enough to work well, though the 6384 makes the 6AR6 look pathetic. The plate rating is 750 volts at 30 watts, which is outrageous for a 6L6 type and more typical of the infamous Mullard EL37. Simply rewire your amp's sockets, and you can use this "Beastatron".
Tests showed that it is indeed a beast. At 300v 50 mA, distortion was 0.77%, lower than that of a typical Tung-Sol 5881. Peak output was 9.8 volts, far more than most 6L6 types and even better than a KT66. It's a shame that so few modern hi-f amps use 6L6s, as the 6384 is a hot little number. When 500v 75 mA was briefly put into the tube, it continued to work without showing red spots on the plate.
All of our stock are military pulls and are tested and guaranteed to function as new.Price is for a Single Tube