Sensibly equivalent¶ to:
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.
Absolute Maximum Operating Conditions¶
Updated January 15, 2015.