(6) Power supplies
Economy in battery current is obtained by using a power unit which contains two separate rotary transformers, one of which is operative only when the "A" set is switched to send, and by providing a separate ON/OFF switch for each service so that those not required may be switched off.

The unit provides H.T. for the whole set from two shunt-wound rotary transformers which step up the 12 volt D.C. input to 275 and 550 volts. The high voltage machine supplies the "A" set P.A. anode and bias voltages and is switched on by means of the pressel switch or by plugging in the morse key.

H.T.1 output is filtered by C38B (R.F.) and C32A (hum). H.T.2 output is filtered by C44A and L18A, the negative side being by-passed by C4CP. R7F which shunts C4CP prevents damage to this condenser if the machine is run on open circuit.

C22C and L17A filter the L.T. line to the valve heaters.

The low voltage inpout to the power supply unit is taken via a 6-pin plug/socket connector and connection to the set is effected by means of a 12-pin connector.

WS19 Power supply circuit diagram

WS19 Drawings of power supply unit

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Rod Beavon     17 Dean's Yard      London  SW1P 3PB

e-mail:  rod.beavon@clara.net