The UM4 tuning indicator from Mullard has dual sensitivity, the 10M2 is directly equivalent. The grid voltage change can be 4.2 V or 12.5 V.
See also EM4.
The control element is clearly visible in the centre of the picture.
The wide glass tube envelope is 26 mm in diameter and, excluding the IO base pins, is 73 mm tall.
References: Datasheet, 3002 & 1040. Type UM4 was first introduced in 1940.
Absolute Maximum Operating Conditions¶
Updated November 18, 2013. shape:wide.glass.tube construction:pinch type:tuning.indicator age:1930.1940 base:io heater:100ma pins:8 pin:1.h pin:2.ic pin:3.a(2) pin:4.t pin:5.g1 pin:6.a(1) pin:7.k pin:8.h