Transistor plug-in units for digital computing systems

Summary form only given, as follows. This paper is divided into two sections. Section I describes the results of approximately six million transistor hours of operation on various types of transistors from four different manufacturers. The data was taken on two different transistor systems containing digital type circuitry and on a set of transistor flip-flop circuits operated under semi-controlled conditions. The types of transistor failures that have occurred will be listed and the general aging trend will be discussed. This section will be accompanied with slides showing some of the circuitry. Based on the above life data along with the experience gained in operating transistor systems, Section II will cite certain conclusions leading to the design of reliable switching-type circuits. In particular a design procedure is demonstrated in the form of a clamped-level multivibrator. This section will show how initial discrepancies in transistor parameters are taken into account along with long term drifts in 'B' and 'Ico.' Aside from the fundamental design practices involved, the multivibrator circuit is chosen because it is relatively difficult to obtain the functional equivalent of a vacuum tube multivibrator due to transistor idiosyncrasies. These idiosyncrasies include low input impedance and hence slow circuit response because of the large coupling capacitors necessary for even small delays. The paper will be concluded with comments regarding clamped vs. unclamped logic and large system operation.