This item was sold by Truvox in 1958 for £2-10-0 (plus £1-2-0 purchase tax!) to plug into their tape recorder. This enabled 2 stations on the medium waveband to be recorded. As can be seen from the photographs it consisted of an aerial connection, iron cored tuning coil and a diode for detection.
It was a plug in crystal set! At that time a senior version covering the long wave too was available for £3-9-6.
In 1962 the senior version was no longer advertised and the MW version was still the same price but the purchase tax had been reduced to 18s-4d. It was illustrated in the Hi Fi yearbook of 1962.
Tuning is by two preset trimmers on each side, which would have only have been useful on the most powerful stations on the MW band. The toggle switch selected which of two stations could be received and so recorded. It is of a neat die cast construction finished in a bronze hammer paint.