We found this simple protection with zener diode in a 1967 Motorola documentation. The zener diode is 18 V, but the components can be changed for operation with other voltages.
This circuit was found in a QST from the 1990s. The circuit expands the scale of a 10V instrument to...
This 8 ohm output amplifier was found in a 1968 Motorola publication. The circuit uses transistors...
This general-purpose preamp configuration was found in the 1960 Mullard transistor reference...