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The DLS1 is not a valve but a thermal delay switch. The warm-up time would match that of a mercury vapour rectifier so that the mercury could be properly ionised before the HT was applied to the anode. Early application of the HT would ruin the rectifier.
The heater is placed close to a bi-metallic strip that bends when hot due to the difference in coefficients of expansion of the two metals forming the strip. At a critical temperature the bending is sufficient for the contact to be made.
The heater ran at 3.0 Volts and 0.6 Amps. The delay time was around 30 seconds and not more than a minute. The current carrying capability of the switch was under 200 mA and the voltage across the connections had to be less than 2,000 Volts.
The heater is on the left and is in the form of a length of coiled wire. The contacts are formed by the two wires seen at the top.
The wide glass tube envelope is 33 mm in diameter and, excluding the base pins, is 108 mm tall.
References: data-sheet & 3002. Type DLS1 was first introduced in 1933. See also 1933 adverts.


Absolute Maximum Operating Conditions
PDF scanned from an original document held by the museum
Updated September 08, 2021.
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