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A PRACTICAL APPROACH TO TRANSIST VACUUM TUBE AMPLIFIERS BY F. J. BECKETT TEKTRONIX, INC. ELECTRONIC INSTRUMENTATION GROUP DISPLAY DEVICES DEVELOPMENT Two articles published in past issues of Service Scope contained information that, in our experience, i s of particular benefit in analyzing circuits. The first article was "Sim- plifying Transistor Linear-Amplifier Analysis" (issue #29, December, 1964). It describes a method for doing an adequate circuit analysis for trouble-shooting or evaluation pur- poses on transistor circuits. It employs "Transresistance" concept rather than the compli- cated characteristic-family parameters. The second article was "Understanding and Using Th6venin's Theorem" (issue #40, October, 1966). It offers a step-by-step explanation on how to apply the principles of ThBvenin's Theorem to analyze and understand how a circuit operates. Now we present three articles that will offer a practical approach to transistor and vacuum-tube amplifiers based on a simple DC analysis. These articles will, by virtue of additional information and tying together of some loose ends, combine and bring into better focus the concepts of "Transresistance." Part I THE TRANSISTOR AMPLIFIER INTRODUCTION Tubes and transistors are often used to- there is an analogy between the two. I t 50, it seems pointless not to pursue this ap- gether to achieve a particular result. Vacu- is true of course, that the two are entire- proach to its logical conclusion. um tubes still serve an important role in ly different in concept; but, so often we I n this first article we will look a t a electronics and will do so for many years come across a situation where one can be transistor amplifier as a simple D C model ; t o come despite a determined move towards explained in terms of the other that it is and then, in the second article, look a t a solid state circuits. very desirable to recognize this fact vacuum-tube amplifier in a similar light. W e will assume that both devices are op- Whether a circuit is designed around Transistor and vacuum tube data give us erated as linear amplifiers and then use vacuum tubes o r transistors or both, it is very little help in the practical sense. P a - the results in a practical way. important to recognize the f