This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This circuit is from a 1982 publication. It is a sequential effect of accelerated and intermittent LEDs....
This PLL with operational amplifiers was found in 1969 documentation. The configuration can be...
Here is a simple source without a transformer for currents up to 50 mA. The voltage depends on the...