[Station X]

I had a look in the second edition of "The Radio Amateur Handbook". This was originally published in July 1940, but my version is an August 1944 reprint.

I also looked at RSGB Bulls from 1939.

Common receiver valves used in home buit transmitters were the 6L6G and 6VG. Unsurprisingly published designs for transmitters dried up after the outbreak of WW2 and the Bulls got smaller due to paper shortages/rationing.

The adaptors used by the Germans could be used in receivers having AL4, AL5, EL2, EL12, 6L6 and 6V6 output valves. Annike could have modified a receiver using one of the valves without the use of an adaptor.

Let me know what further info you need. Presumably the construction of the kit is to be described in the novel, but it's difficult to know what would actually fit in with the plot.

As for the Royal Signals transmitter/receiver this would presumably have been relatively high powered, rather than the low power sets such as the 19 set used in tanks etc?