The 5670 is a rugged special quality double triode developed from the 2C51. Applications include: mixers, oscillators and amplifiers operating to VHF. Also for use in multivibrators, synchronising amplifiers and industrial control. For airborne use it was certified up to 80,000 feet. It additionally had low microphany. The latter attribute brought it to the attention of audio amplifier builders.
The twin triode sections with screen between.
The ridge in the anode confirs rigidity. The flattened oval cathode tube and grid are easily visible.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 37 mm tall.
Reference: Datasheet. Type 5670 was first introduced in 1952.