Microphone Amplifier (CB21357E)

This preamp circuit was found in English documentation. Transistors are general-purpose, like the more modern BC549 equivalents than those indicated.

Telephone dialer (CB9235E)
This circuit was obtained in Radio Electronics from the 90s. The integrated circuit is uncommon...
10 Hour Digital Clock (CB17007E)
This 4-digit digital clock for hours and minutes with CMOS integrated circuits was found in a 1995...
Preamplifier for Microphone (MSB062E)
This circuit is indicated to operation with low intensity sources such as electret microphones and...