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AC/HL

Sensibly equivalent to:
354V 41MHL A30D AR17 CV399 CV1037 CV2811 D4 HL4 MH4 MHL4 NR31 VR37
See also:
Shortpath Construction - 1929 Advert
    
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The AC/HL indirectly heated amplifier triode makes use of the 'Shortpath' technique construction.
This valve type, manufactured in the early 1930s and sold under the Mazda label, is the direct successor of the Landmark Cosmos AC/G of 1927/28.
The AC/HL was a very long-lived valve. Many originals survive in working order and during the late 1960s it was claimed that a specimen removed from obsolete BBC studio equipment still met the original specification for a new valve after over 250,000 hours in service! Note that the Type No. AC/HL was also used by other brands of valve, including Lissen.
The oblique stroke is sometimes omitted in listings (ACHL instead of AC/HL).
The zinc paint has broken away at the top of the valve to reveal the etched lettering and the top of the electrodes.
The balloon envelope is 56 mm in diameter and, excluding the B5 base pins, is 109 mm tall.
References: Private communication, datasheet & 1043. Type AC/HL 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
4.0
1.0
200
-2.75
6
10,000
3.5
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated January 15, 2015.
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