Sunvic hot-wire vacuum switch type 603

This valve measures 142x25mm overall

This is a Sunvic hot-wire vacuum switch, type 603, style 137727. The label reads: Control current must not exceed 42mA. Control circuit resistance 1800 ohms approx. Unless one lead is common to the control circuit, the series resistance must be in 2 parts, 1 in each lead and neither part must be less that 500 ohms. Patent No. 354020 & others. It is marked CC 23.0 / 23.5mA, and dated 12 June 1979. See also 602