The 6X8A is a triode pentode for use as oscillator and mixer in receivers using an IF of up to 40 MHz. The 6X8A can be used for AM/FM receivers as well as television receivers.
The A suffic denotes a variant to the basic 6X8. In this case the variation is to the heater thermal characteristics.
Types 19X8 and 5X8 differ only in heater rating. Type 6X8 was introduced in 1951.
Looking into the U shaped anode of the triode.
The image is taken at 90 degrees to the electron flow. The central cathode is a rectangular box with the triode to the right and the pentode to the left. Both anodes are U shaped with a flat face towards the cathode. The getter holder is fixed to the top of the beam plate.
The central structure. The pentode is at the top. Note the space between the cathode and the control grids.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 48 mm tall.
Reference: Datasheet. Type 6X8A was first introduced in 1952.