Visual dial indicator (CB9300E)

This circuit was obtained in a Popular Electronics of the 90s. The circuit can be assembled with equivalent components.

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Telephone Spy (CB18493E)
We found this circuit in an English documentation from 1980. The circuit can be assembled with the...
20 MHz Colpitts Oscillator (CB5122E)
This circuit can generate signals in the range from 1 to 20 kHz, depending on the crystal. The...
Low Pass Filter (CB13078E)
In the figure we have a low-pass filter, with a cutoff frequency of 10 kHz, also suggested by...