AC Mains TRF
The Cossor MR133 is one of Cossor's earliest AC mains sets and dates from 1930. It requires an external loudspeaker, and is very much in the "radio-in-a-box" style of the previous decade.
It is a simple and conventional TRF circuit tuning over two wave bands.
The valve line-up is:
354V Leaky grid detector
PM24A Pentode output
U10 Mains rectifier
Two aerial inputs are provided, one with a trimmer in circuit. The detector circuit is entirely conventional. One stage of tuning with capacitative reaction is employed. The triode detector is transformer coupled to the pentode output stage. The loudspeaker is fed from a choke in the anode circuit of the output valve.
A full-wave rectifier strapped in a half-wave configuration provides the choke-smoothed HT supply of slightly over 130 volts. Bias for the output valve is derived from a resistor in the negative HT return.
Provision is made for an electrical gramophone pick-up to be conected to the grid of the detector.
In 1930 the set cost Ł11 10s 0d.
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