Sensibly equivalent¶ to:
This ML4 looks to be an early example as it is enclosed in a balloon envelope. We have another ML4 in the later classic envelope.
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 ML4 was quite widely used as an RF oscillator, as a single-valve phase splitter, and as a driver for larger valves.
As close a view as is possible with the Olympus E20 plus 4 dioptre lenses.
The mesh anode, grid, cathode tube and heater are all visible.
The Marconi Valve logo is etched into the envelope as is the BVA logo.
This close-up was taken with a new Nikon D80 camera. The electrodes are fully revealed.
The balloon envelope is 50 mm in diameter and, excluding the B5 base pins, is 105 mm tall.
References: Data-sheet, 1040 & 1043. Type ML4 was first introduced in 1929. See also 1929 adverts.
Absolute Maximum Operating Conditions¶
Updated November 13, 2021.