This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
The sensor is an NTC and in the connection as shown in figure (a) we have the trigger with the...
This oscillator configuration with the operational 741 was obtained in a European documentation from the...
Found in Motorola's 1965 manual, this full-wave dimmer controls a load that depends on the used...