Two-tone solar buzzer (CB20493E)

This circuit was found in a 1991 publication. The transistor can be a general-purpose type.

Variable Voltage Controlled Attenuator (CB4236E)
This circuit was obtained from an American 80's documentation. The balanced mixer can be shown in...
12 V output for 5 V regulators (CB20681E)
Found in an Electronic Design of the 90's, this circuit provides an additional 12 V output to a 5...
VCO 4046 (CB15464E)
The CMOS 4046 integrated circuit is seldom used, both due to the difficulty of finding it and the...