An all-electric clock
Paul Vigoureux, H E Stoakes · Proceedings of the Physical Society · 1940
The synchronous motor usually employed for obtaining seconds' intervals from a 1 kc./sec. source controlled by a high-frequency crystal oscillator is replaced by three multi-vibrators whose controlled periods are 10, 100, and 1000 times that of the source respectively. On account of the extremely sharp rise of current in the multivibrator circuits, the intervals provided by the seconds multi-vibrator are equal to within 10 micro-seconds. Each multi-vibrator consists of a single triode-pentode valve, injection from one stage to the next being effected on the suppressor grid of the pentode section, a method of injection which has proved superior to anode-circuit or grid-circuit injection. A check that the multi-vibrators are in step is obtained by using their outputs to charge a condenser through the coils of a cathode-ray oscillograph whose time base is synchronized by the 1 kc./sec. input.