This old amplifying stage was found in radios and small amplifiers of the time. The circuit is from Mullard's transistor reference manual.
This simple circuit controls the brightness of an LED from LDRs, NTCs, PTCs or other resistive sensors....
This sonic relay or vox was found in a Popular Electronics from the 90's. The power MOSFET can be of...
This circuit has been found in an old documentation, but can be used as input shield for current...