VCO with optocoupler (CB21501E)

This circuit was found in a 1967 Raytheon optoelectronics manual. The circuit uses tubes.

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Recording Head Amplifier (CB26167E)
This circuit was found in the 1992 Radio Electronics Handbook. It is used to test VCR recording heads....
Micro Touch Control (CB20312E)
This circuit turns a relay on or off by touching the sensors or by connecting sensors at these...
Transistorized Electronic Organ (CB13994E)
This article is from the Italian magazine Sperimentare number 11 of 1975. It can be assembled with...