42 kHz oscillator (CB21805E)

This circuit was used as an eraser for old tape recorders. The circuit is from a 1960 Mullard transistor manual.

Gain controled shield for operational (CB8777E)
This circuit was found in a 90s Popular Electronics. With it, using a 4066, it is possible to...
Temperature compensator for VFO (CB8096E)
This circuit was found in a Popular Electronics from the 90s. The circuit has temperature...
AC Amplifier with LM3900 (CB14180E)
In the figure we have the basic application of an LM3900 transconductance amplifier, as suggested by...