W1239 Wavemeter (RAF code 10T/50)

 This looked slightly odd as it seemed to be upside down. The handle is underneath and the rubber feet on top. At first I thought it was mounted upside down in its wooden case but, as there are two copper lined compartments of different sizes, the chassis only fits one way round, so it must be arranged this way for operational reasons. After some consideration it's possible that because the box is so well screened provision needed to be made for some basic cooling of the valves and transformer. The ventilation hole is positioned so that fitting a carrying handle at the centre of gravity is compromised so the handle was located on the opposite side of the box. This means that in storage the handle would be uppermost and the box would rest upside down on its feet and when the box is initially set down it will rest on the 4 rubber feet seen below. It wouldn't appear odd as a lid would have been present.

There are an additional 4 rubber feet on the back of the box so its likely that the wavemeter is normally operated lying on its back.

 The instrument uses 4 valves.

A magic eye, a VR67, a 6X5G and a VR92 (an EA50 B3G-based diode). As the last valve must have been awkward to source, or if it failed frequently, whatever the reason, it has a spare mounted between the VR67 and 6X5G. The VR67 is a triode (L63 or 6J5 equivalent). The 6X5G is a full wave rectifier and the EA50 a diode capable of operating in the VHF band.

 A really high Q 3-turn tuning coil with a single turn input coupling coil adjacent. The outer plating doesn't look like silver, I've seen it before in WW2 equipments..what is it?

Rectifier diode, EA50.

 Thanks to Tony Waller for finding a reference to this upside down wavemeter, "listed as "RDF ancillary equipment and is described in AP2563".

I used to have an RDF receiver years ago when they were being sold to pick up ITV sound when Band III was first opened up for TV broadcasting.


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