This circuit is from a 1976 amateur radio manual. The transistor can be the BD136 and the frequency adjustment is done in a potentiometer. The supply can be done with voltages from 6 to 15 V.
This series LED circuit was found in the February 1992 issue of Radio Electronics magazine. The...
We found this circuit in the Linear Applications Handbook by National Semiconductor. The circuit uses...
The noise comes from the PN junction of a common silicon diode. Since no gain is given by the...