Crystal converter (CB7327E)

This circuit was found in a Popular Electronics from the 90's. The circuit can be used to convert signals to frequencies up to 25 MHz.

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Plant soil heater (CB7964E)
This circuit was found in a 90’s 303 Circuits. The components are from the period and the heating...
Regulated power supply (CB21698E)
The transformer in this power supply can have a secondary winding from 1 to 15 A of current....
Negative Voltage Regulator (CB15903E)
This circuit is suggested by National Semiconductor and makes use of the negative regulator LM2990...