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We found this circuit in the November 1992 issue of Radio Electronics magazine. The 30V power supply must be symmetrical and preamplification stages are included.
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...
This circuit reproduces the dial noise in a small speaker. The transistor can be a general-purpose type....
Found in American documentation from the 90s, this circuit provides three timings given by the...