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ML4

Sensibly equivalent to:
AC/P CV1179 NR57
    
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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.

 

Pin Connections
B5
1
2
3
4
5
a
g1
h
h
k

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
Pout
4.0
1.0
200
-13.5
17
3,700
2.7
0.65W
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated January 15, 2015.
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