Made in G.Britain by GEC.
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. Loctal socket.
Vh = 50v....Ih = 100mA.................RMSin (max) = 250v....Irect (max) = 100mA
Nos in original box. Never been used. Matched pair are available.