EIA TEP137-1962

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.