A Vox 100 watt hybrid PA amplifier - preamp

Some details of the solid state preamp of a hybrid 100 watt PA amplifier assembled by Triumph Electronics for Vox (Jennings Musical Industries) in 1967. The power amp is all valve (4 x EL34). General pictures of the amp can be found .

Potentiometers are made by Egen, date codes "AO" = January 1967. The meter is a modern replacement. The five microphone channels have a single AC107 germanium transistor each. The hi-impedance channel has a Mullard OC45 (germanium) and a BC108 (silicon). The mixer board - volume, treble and bass - has an AC107 and OC45.

Wiring carrying the supply voltage and the signals out from the channel boards is hooked up on insulated pins. The octal connectors, marked with red and yellow tape, connect up with the marked sockets in the power amp.

The aluminium housings behind the fascia are held on by the tension of the screws holding the potentiometers on, a simple and elegant solution.

The high impedance input

Microphone input

Details of the power amp to follow.

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