The 5670 is a rugged special quality double triode developed from the 2C51 the 5670W should indicate a special quality variant but there is little visual difference between them. It is possible that the suffix has less meaning when the original Type was a special quality type.
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 GE logo.
Thick mica sheets dampen out vibration and help make the valve rugged.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 36 mm tall.
Reference: Datasheet. Type 5670W was first introduced in 1952.