VI507 / REL21 / CV86 spark gap switch.

This device measures 50x15mm overall.

There are two variants of this device. The REL21 has tungsten tipped electrodes with a gap of 0.4mm. The electrodes are surrounded by a glass bead and ceramic sleeves. The earlier CV86 was the Mk.I type and has electrodes surrounded by a short piece of glass tubing to confine the glow discharge.

This device is gas filled with argon, plus a small amount of mercury, and in Mk.II form can handle 120kW peak. These were used in the CHL (Chain Home Low) coastal defence system in WWII, as well as the naval Type 291 air/surface warning radar.

Above: REL21. Below: CV86