The VP1321 is a variable μ pentode with external metallising. The 200 mA heater requirement was to allow the valve to be operated in a chain across the mains and thus be used in mains receivers without mains transformers. This both saved cost and allowed operation on DC mains as well as AC.
The classic envelope is 38 mm in diameter and, excluding the B7 base pins, is 104 mm tall.
References: Datasheet & 1043. Type VP1321 was first introduced in 1934.
Absolute Maximum Operating Conditions¶
Updated December13, 2012. shape:classic construction:pinch type:pentode age:1930.1940 base:b7 heater:200ma pins:7 pin:1.m pin:2.g1 pin:3.g3 pin:4.h pin:5.h pin:6.k pin:7.g2 pin:tc.a