The U101 is a very late (1970s or possibly 1980s) specimen of an indirectly heated half wave rectifier of a type introduced in the 1940s. We also have what appears to be the prototype of the U101, M-OVs E1795.
Interestingly, although it was made at a time when most brands were buying and relabelling foreign valves, this exhibit seems to bear all the hallmarks of a genuine British-made product.
The shiny black plastic spigot is essentially an M-OV feature (Mullard, Continental and US equivalents were all fitted with metal spigots). Note also the characteristic M-OV style of marking and date code, although the GEC label suggests that the valve was made after the Hammersmith and Chelmsford factories had been amalgamated.
The rectifier is designed for use in universal equipment with a series heater chain.
The maximum reservoir capacitor is 32 µF and the minimum series resistance has to be 100 Ohms.
The wide glass tube envelope is 30 mm in diameter and, excluding the B8B base pins, is 56 mm tall.
References: Private communication & 1040.
Absolute Maximum Operating Conditions¶
Updated November 20, 2016.