The 6973 is an audio beam tetrode for use in Hi-Fi amplifiers and was designed by RCA in about 1957 - just as stereo amplification was taking off.
The 6973 as a push-pull pair operating in Class AB1 was rated at 20 Watts output at 1.5% THD with 350 Volts on the anodes. For a Class A single ended amplifier the anode voltage would be 250 Volts. The figures in the table below are for the Class A use.
Robert Coleman says that these were used as a pair driving two KT66s in a Leslie rotating speaker.
The RCA name.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 70 mm tall.
Reference: Datasheet. Type 6973 was first introduced in 1957.
Absolute Maximum Operating Conditions¶
Updated July 21, 2017. shape:thin.glass.tube construction:all.glass type:beam.tetrode age:1950.1960 base:b9a heater:6.3v pins:9 pin:1.g2 pin:2.- pin:3.g1 pin:4.h pin:5.h pin:6.g1 pin:7.k.bp pin:8.g2 pin:9.a