Found in a 1924 documentation, this circuit is powered by 3 batteries, two of which are high voltage. The output is a high impedance headphone jack.
This interesting circuit, which can be used as an alarm, was found in a 1997 documentation. It...
We found this circuit in the National Semiconductor FET manual. The components are calculated...
The presented circuit is suggested by Texas Instruments (www.ti.com) in its Application Report...