The "Hard-Bottoming" Technique in Nuclear Instrumentation Circuit Design

It is very desirable to operate vacuum tubes in such a manner that the operation of the over-all circuit is essentially independent of large changes in tube characteristics. The technique of "hard-bottoming" of vacuum tubes in two-state circuits obtains operation that, in many cases, is unchanged until the vacuum tubes are almost completely inoperative by ordinary standards. Negative feedback has, of course, been used for many years to stabilize amplifier circuits, but the use of hard bottoming has not become as widespread. The Physical Electronics Group of the Physics Division, ORNL, has, over the last few years, applied the hard-bottoming principle to many circuits used in nuclear instrumentation. In scaling circuits, it represents as large a step forward in design as did the addition of coupling diodes by Higinbotham. Precision timing circuits are made possible by use of this principle. These applications are described.