The AC/OC4 is an octode frequency changer or mixer. It has a 4.0 Volt AC heater. The oscillator anode would be operated at 90 Volts. The Mullard FC4 is very similar in rating.
The reverse is plain zinc paint with a reference code near the base.
The classic envelope is 46 mm in diameter, and excluding the B7 base pins is 113 mm tall.
Absolute Maximum Operating Conditions¶
Updated March 19, 2014. shape:classic construction:pinch type:octode age:1930.1940 base:b7 heater:4.0v pins:7 pin:1.g2 pin:2.g1 pin:3.g3.g5 pin:4.h pin:5.h pin:6.m.k pin:7.a pin:tc.g4