Permanent magnet detector (CB22463E)

We found this circuit in Popular Electronics from 1992. Transistors admit equivalents.

Preamplifier and Tone Generator (CB20004E)
This is a combined circuit of tone generator and preamplifier. We found it in a 1975...
Multipurpose Alarm (CB17301E)
We found this simple alarm circuit in a 1986 documentation. The circuit uses sensors of the NA...
PLL LM3900 (CB14199E)
We found this circuit in the Linear Applications Handbook by National Semiconductor. The base is...