Modulated light receiver (CB21790E)

We found this circuit in a Mullard manual from 1960. The transistor is a phototransistor of the time. The gain is 3 dB.

Touch Sensor 4013 (CB15761E)
This circuit fires at the touch of a sensor, passing its output from high to low in a time given by...
Binary Counter using Relays (CB6607E)
This circuit was found in a 1967 US publication. In it we have the implementation of a ring...
Touch Volume Control (CB12470E)
The strength of an audio signal can be controlled by touching sensors. Keeping the finger in...