The 6BX7GT double triode was designed for use in 525 line television receivers as frame oscillator and amplifier. Consequently it is built to withstand high peak voltages and also a high cathode current.
Haltron were resellers not the original maker.
Although not imagined at the time of original manufacture, the 6BX7GT has been used as an audio amplifier.
The twin triode sections with substantial anodes and copper supports for the grids.
Side view of the anode - the flange is located in the centre of the working face where maximum heat is generated.