The 37 is a low impedance low gain amplifier triode. One of its original intended applications was as an 'anode bend' signal detector. The 'anode bend' detector gives a reasonable audio gain with appreciably less audio distortion than the better-known 'grid-leak' triode detector. Use of the Type 37 as a detector became obsolete when superhets with AVC and double-diode-triode became the norm. However, the Type 37 lived on for another decade in its general-purpose role.
The General Electric name on the base cap.
A close-up view of the top of the triode. The grid winding extends outside the coated cathode tube.
The classic envelope is 38 mm in diameter and, excluding the UX5 base pins, is 88 mm tall.
References: Datasheet, 1040 & 1043. Type 37 was first introduced in 1936.