The VLS631 is a thermal delay tube.

The heater will take a defined time to heat the bi-metallic strip to the point that the contacts will make. Such switches were used to delay the HT voltages until the heaters of the valves were at the correct temperatures. Mercury vapour rectifiers and travelling wave tubes are examples of devices that are protected by thermal delay switches.

The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 44 mm tall.

 
Absolute Maximum Operating Conditions

Delay	Vh	Ah	Va	mAa
	6.3	0.5	220	1,000

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 01 February 2008 {find valves by name}