Despite being from a 1969 publication, the transistors used have current equivalents such as BC548 and BC558. The circuit generates signals from 1 500 to 20 000 Hz and 4 scales.
We found this configuration in the Linear Applications Handbook of the National Semiconductor of...
This circuit is an application for an operational amplifier with field effect transistors from...
This circuit was found in an old Radio Electronics, but can still be assembled as the components are...