This active tone control circuit was found in American documentation from the 90's. The transistor can be general purpose or low noise with high gain.
We found this sensitive moisture detector in an old documentation. The circuit uses a common JFET,...
This circuit, with the assembly in a contact matrix, was found in a publication from the 90s. The...
This modulator circuit for transmitters was found in American documentation from 1964. It can be...