DC Voltmeter with CA3140 (CB21718E)

We found this circuit in an internet documentation. The circuit uses a 1 mA instrument, and the power supply consists of two 9 V batteries.

Electronic Fuse (CB10347E)
This circuit was found on a Radio Elettronica (Italy) from April 1974. The circuit can still be...
Second Order 1 kHz Low Pass Filter (CB13444E)
This filter was found in a 1975 American technical publication. The filter can be of any type and...
Amplifier OC30 (CB18565E)
This is a commercial circuit of a transistor amplifier of some watts with the OC30 transistor. The 12 V...