5 valve portable
In the late 1920's several companies produced portable sets of the "5 triode type". Although the high inter-electrode capacity of triode valves make them rather unsuitable for stable HF stages, by limiting their gain it is just about possible to get some useful amplification at radio frequencies.
The Pye 25 series were produced in 1927 (25A), 1928 (25B) and 1929 (25C). The 1928 model is illustrated here.
The sets all employ a 5 valve circuit using a tuned frame aerial. There are two HF stages, aperiodically coupled by HF chokes, a leaky grid detector and two transformer coupled LF stages, together with an internal moving iron loudspeaker. The principal difference between the models is that the A and B versions obtain reaction by a moving coil coupled to the frame aerial, whereas in model C a differential condenser is used. The tuning dial is calibrated 0-100.
The valve line-up is:
PM1 HF (4 off) used in both HF stages,
detector and first LFstage
Originally the "C" model was advertised at Ł22 5s.0d plus a Marconi Royalty of Ł1 5s.0d. including batteries. A spare accumulator cost 14s. 6d. and the HT battery (108v) was 15s. 0d. The following year the price, including Royalty, was Ł19 19s.
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