This circuit was obtained from Dutch documentation from 1964. The components are of the time, but current equivalents such as BC548 to BC108 can be used.
This circuit is from a Radio Electronics issue of May 1972. It consists of a commercial heating...
Found in the American 73 magazine for radio amateurs, this circuit can test common quartz...
This circuit is from the 1995 National Semiuconductor Linear Application Handbook. The technique...