3-channel preamp (T484E)

This 4-tube circuit was found in an American publication from 1947. It is intended for audio distribution lines using a transformer source.

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Bargraph or Mobile Bar Indicator using the 4093 (CB13181E)
The circuit shown in the figure, activates a bar of 4 LEDs with an audio signal applied to its...
RPM Counter (CB18759E)
This sophisticated RPM counter circuit with discrete integrated circuits was obtained in a 1993...
Telephone Dialer for Alarm (CB18755E)
This circuit was found in documentation from the 90s. Its purpose is to dial a programmed number...