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MH41

Sensibly equivalent to:
41MH AC2/HL CV1505 HLA1
    
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The MH41 is a mains triode that has the 1930s UK standard 4 Volt 1 Amp heater. The cathode assembly is a flattened tube and the grid is wound on notched rods. The anode is a bright mesh.
The valve low impedance device and designed for audio frequencies.
The MH41 was a souped-up MH4 and was M-OV's answer to the Mullard Type 994V as a high-gain detector triode. Unfortunately, by the time the MH41 hit the market the real need (for modern superhets) was for double-diode-triodes (eg. the M-OV MHD4, etc.).
However, the MH41 saw service as an audio pre-amplifier and in professional applications. MH4s and early MH41s (such as illustrated) were inclined to be a bit hummy for high-gain use so a low-noise triode, the MH40, was also produced for professional users. Later MH41s were redesigned to reduce hum and noise and were used by the BBC and other professional organisations.
The reason for the mesh anode is that fairly large amounts of gas are evolved when the coated cathode surface is activated during manufacture. Very much smaller amounts may be evolved when a valve is first used after a prolonged period of disuse. Making the electrode structure porous to gases helps evolved gas to flow away from the active regions of the valve and towards the pump stem or the internal getter, as the case may be. Even some modern valves have openings in the anode structure for similar reasons.
The balloon envelope is 42 mm in diameter and, excluding the B5 base pins, is 100 mm tall.
References: Datasheet & 1040. Type MH41 was first introduced in 1933.

 

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
4.0
1.0
200
-1.5
5.2
13,300
6.0
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated December02, 2012.
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