The 25Z6GT is a pair of rectifiers in a single envelope with a common heater connection. This construction offers a flexibility in circuit design. The 25Z6GT can be used as a half wave rectifier with both sections in parallel. A full wave rectifier by joining the cathodes or as a voltage doubler.
Electrically the 25Z6GT is identical to the 25Z6 and 25Z5.
The glass has both printed and etched identification.
The two sections can be seen. Each anode has a wing attached to a support rod to maximise heat transfer. The heater construction is also revealed. The thin tungsten heater wire is slip coated and folded so that the heater has six strands within the cathode tube.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 71 mm tall.
References: Datasheet & 1040. Type 25Z6GT was first introduced in 1938.