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Nelson Tansley Receiver

This design of public address amplifier is much less common than the Ripper unit, and is also a much simpler design. The schematic is shown here.

PA schematic

24v positive supply comes in through a reverse polarity protection diode and is limited against excessive voltage by the 5W zener diode. The output Darlingtons are biased by the resistor/zener diode combinations. Incoming audio from the RCH lines is fed to the transformer which phase splits to feed the output Darlingtons. Audio feedback comes to the transformer from the loudspeaker output via a 15k resistor (which also determines the overall gain of the amplifier).

A repair service for these units is available from GoToPCs - just email me (see Home page)