M-OV's first indirectly-heated HT rectifiers were the MU12 and MU14. These were in fact the same valve but only a minority of each production batch were good enough to withstand the full rating when tested. These few were labelled MU14.
Initial production was the balloon shape but later production moved to this classic style.
The anodes are ribbed for dimensional stability of the thin nickel sheet.
The Osram brand label.
This side is clear and the construction can be seen. The rectangular cathode tube is threaded by the insulated heater folded into four.
With a little enhancement.
The classic envelope is 44 mm in diameter and excluding the B4 base pins, is 103 mm tall.
References: Data-sheet & 1043. Type MU14 was first introduced in 1933. See also1933 adverts.
