Application of Conventional Vacuum Tubes in Unconventional Circuits

This paper describes some out-of-the-ordinary, yet simple and interesting, vacuum tube applications. It illustrates how conventional vacuum tubes can be used in circuits which impose unusual requirements for grid current, noise, and life. Analysis of circuit requirements and knowledge of tube performance characteristics frequently make possible adjustment of operating conditions to give the desired results. A number of circuits to indicate the practicability of this procedure are described, and are used to illustrate simple and logical methods of analyzing circuit operation. 1. A two-stage photo amplifier relay circuit operating directly on the alternating-current line and using a voltage divider, one resistor, and three condensers as circuit parts. 2. A sensitive photo amplifier circuit using a pentode as the load resistor for a phototube and a standard tube as a reliable and sensitive electrometer tube feeding a low priced indicating instrument. 3. A modification of (2) to provide variable-range, variable-sensitivity characteristics. 4. A simple vacuum tube circuit in which standard unselected tubes can be used to multiply currents on the order of 10^-12amperes by a definite factor (fixed by the circuit elements and not by the tubes) to such values that they can be easily read on an insensitive milliammeter. 5. A simple capacitance operated relay working on the alternating-current line, using metal tubes and only a few inexpensive circuit parts.