This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time...
This circuit generates noise pulses for audio equipment probes. The circuit is from a 90’s 303...
This circuit was found in a 1970s General Electric documentation. This circuit already used an...