Oil change computer (CB6373E)

This electrochemical circuit monitors the conductivity of the oil indicating when to change it. The circuit is from an 1967 American documentation.

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Sensitive photoelectric relay (CB7893E)
Found in American documentation from the 90's, this circuit activates a 12 V sensitive relay. The...
15 V x 2A Power Supply (CB15935E)
This circuit, suggested by Motorola, provides a voltage of 15 V under a current of up to 2 A. The...
Interval timer (CB7504E)
Among other applications, the 1960 Sylvania transistor manual indicates this timer for chess...