The 25Z6G contains a a pair of rectifiers. This rectifier was designed for AC/DC receivers using a 110 to 120 V mains input. The rectifiers can be used to build full wave, half wave and voltage doubler circuits. In the half wave mode both sections may be used in parallel.
Electrically the 25Z6G is identical to the 25Z6, 25Z6GT and 25Z5.
The rectifiers have a small central cathode and the anode has side wings to dissipate heat. Wires passing through the top mica press against the envelope to hold the electrodes steady.
The insulated heater passes four times through the cathode tube.
The classic envelope is 38 mm in diameter, and excluding the IO base pins is 92 mm tall.
References: Datasheet & 1040. Type 25Z6G was first introduced in 1936.