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: Datasheet, 1040 & 1043. Type ML4 was first introduced in 1929.
Absolute Maximum Operating Conditions¶
Updated January 15, 2015. shape:balloon construction:pinch type:triode age:1920.1930 base:b5 heater:4.0v pins:5 pin:1.a pin:2.g1 pin:3.h pin:4.h pin:5.k