572 B transmitter triode

This triode is very often used as a final stage in amateur stations. Because of its very high mu (amplification factor =160), it is ideally suited for grounded grid operation. 

It has a M-shaped filament (thoriated tungsten), rating is 6.3 V, 4 A, and a biplanar grid. The plate is made from graphite with external high-temperature getter (zirconium coating?), thus showing quite a light grey colour. At the base of the bulb, an additional small Barium flash getter is added. The tube is able to handle very high plate voltages, 3.500 V being the nominal value, but due to the big distance of the anode to all other electrodes, I suspect much higher voltages (up to 10 kV?) could easily be handled in special applications. Plate power dissipation may reach 160 Watts (some manufacturers only allowing 125 Watts). 

Svetlana has created from this type a whole series of tubes with graduated mutual conductances (SV 572-160, SV 572-30, -10, -3), especially designed for power stages in large HiFi-amplifiers. They also have their plate connection to the base, thus avoiding a top cap, but being limited to voltages up to about 1000 Volts. They also allow a maximum plate dissipation of 125 W only.