Double door bell (CB7559E)

Found in an Elektor from the 90's, this double door-bell drive circuit switches a relay by triggering different points.

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Tunnel diode 100 kHz oscillator (CB9417E)
This circuit is from an American publication of 1977. The tunnel diode admits equivalents and the...
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This circuit was obtained from an English magazine from 1976. The circuit operates two LEDs and...
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Found in 90s Popular Electronics this circuit amplifies signals over a wide range of frequencies....