This 1924 receiver uses a battery for the tube filaments and a high voltage battery for the amplifier and detector circuit. The speaker is kind of high impedance era.
This circuit was found in a 1967 Electronic Design. The circuit makes use of components from the...
This alarm circuit was found in April 1975 Radio Electronics magazine. The circuit uses a 12 V...
This latching alarm using simple contact relay was found in an English documentation from 1980. The...