INTRODUCTION

NEED FOR A RATING SYSTEM

The conditions under which an electron tube may be operated are limited by fundamental capabilities of' the tube itself. Physical limitations exist, for example, in the permissible temperatures at which the various electrodes may be operated, in the amount of current which can be emitted by the cathode, and in the voltage gradients which may be permitted between the various tube elements.

Maximum tube ratings have been established to define these various physical limitations of the tube in terms of readily measurable quantities. The numerical quantities presented as maximum ratings indicate the limiting operating values required to assure satisfactory tube life and performance.

Before the value of any rating can become meaningful, the rating system on which the rating is based must be specìfied. The system must define the interpretation required of the numerical values and indicate the procedure necessary to determine whether or not a tube is operating within its rating.

Until the present time, two rating systems have been commonly used in conjunction with receiving tubes, the Design-Center System and the Absolute-Maximum System.

The problems created by their deficiencies have greatly intensified in recent years primarily as a result of the greatly increased scope of receiving tube applications.

To overcome the deficiencies encountered with the two rating systems in current use Maximum System" has been developed.