Sensibly equivalent¶ to:
The ML4 was quite widely used as an RF oscillator, as a single-valve phase splitter, and as a driver for larger valves.
Although sometimes listed as a triode output valve, the ML4 was the definitive descendent of the famous (or infamous) Type KL1 of 1926 and was primarily a professional and military type, little used in domestic radios.
The other side of the envelope is also opaque but it does have the Osram label.
See also ML4
The classic envelope is 38 mm in diameter and, excluding the B5 base pins, is 95 mm tall.
References: Datasheet, 1040 & 1043. Type ML4 was first introduced in 1929.
Absolute Maximum Operating Conditions¶
Updated February 17, 2015.