The W101 is a variable μ amplifier pentode on a Loctal (B8B) base. Use would be at RF or IF frequencies in AC/DC receiver equipment. The W81 is the same valve but fitted with a 6.3 Volt heater for AC mains sets.
The Loctal base pins.
Thanks to Mark Mallison for sending the images.
The wide glass tube envelope is 32 mm in diameter, and excluding the B8B base pins is 59 mm tall.
Reference: 1040. Type W101 was first introduced in 1947.
Absolute Maximum Operating Conditions¶
Updated March 04, 2020. shape:wide.glass.tube construction:all.glass type:pentode age:1940.1950 base:b8b heater:6.3v pins:8 pin:1.h pin:2.a pin:3.g2 pin:4.g3 pin:5.s pin:6.g1 pin:7.k pin:8.h