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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Half-wave motor control (CB8020E)
This half-wave regenerative control was found in an old RCA manual. The circuit can be designed...
48 V power supply LM340 (CB14263E)
National Semiconductor suggests this circuit in its 1994 Linear Applications Handbook. The D3...
Code Switch (CB1354E)
This 3-digit code switch was obtained from an old American documentation. The capacitor is 470 uF...