The BT89 is a small Xenon Thyratron that would have been designed as a pulse modulator. Around the type designation on the envelope is some lettering. At the top it says Thyratron and at the bottom it reads AEI Ltd Lincoln.
The anode can swing to -1,500 Volts and the grid can reach -100 Volts. The mean anode current is given but the peak current is 2 Amps. That is a 2 kW pulse switching ability.
The wide glass tube envelope is 36 mm in diameter, and excluding the B4 base pins is 99 mm tall.
Absolute Maximum Operating Conditions¶
Updated February 21, 2014. shape:wide.glass.tube construction:glass.foot type:thyratron age:1950.1960 base:b4 heater:2.5v pins:4 pin:1.- pin:2.g1 pin:3.f pin:4.f pin:tc.a