Photo-sensitive resistor in an overload-preventing arrangement
Javier Miranda · IRE Transactions on Audio · 1960
The signal from a pre-amplifier or tuner is supplied to the input terminals of the power amplifier by means of a voltage-dividing network, the element in parallel to these input terminals being a photo-sensitive resistor of new design. Facing this photo-resistor in a lightproof enclosure is a neon lamp connected to the output voltage of the amplifier. Because a neon lamp ignites at a fixed voltage, the value of the photo-resistor resistance will be decreased as soon as this voltage is reached. Consequently, the input signal to the amplifier will be decreased as well, making overload substantially impossible.