In this 1968 circuit the approach of the key which is a circuit tuned to the tube oscillator causes the relay to lock. The relay is of high voltage type and the secondary of the transformer is approximately 150 V.
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In this 1968 circuit the approach of the key which is a circuit tuned to the tube oscillator causes the relay to lock. The relay is of high voltage type and the secondary of the transformer is approximately 150 V.