741 Filter (CB24265E)

The 1 kHz tuned filter shown uses a 741 op-amp. The components can be re-scaled to suit the desired frequency.

Simple metronome (CB7285E)
Found in Popular Electronics from the 90s, this circuit uses a 2N2646 and a general-purpose transistor...
Crystal Oscillator (CB6522E)
The crystal frequency of this circuit found in an American documentation is limited only by the...
Two megaphones (CB23658E)
These two circuits were found in Radio Electronics magazine from February 1960. The transistor is a power...