bron voor condensatoren en Vintage audiocomponenten
and their significance
This article is a part of the
tube information as presented by the
RCA VICTOR Tube Division,
It is largely based on
standards of the Radio Manufacturers Association. (1940)
most of the info given here is also applicable
to amplifier and rectifier
A rating is a designation, as established by definite standards, of an
operating limit of a tube. Tubes are rated by either of two systems, i.e., the
"absolute maximum" system or the "design- center maximum"
system. Of the two, the absolute maximum system is the older and dates back to
the beginning of tubes. With either system, each maximum rating for a given
tube type must be considered in relation to all other maximum ratings for that
type, so that no one maximum rating will be exceeded in utilizing any other
maximum rating. For convenience in referring to these two systems, the former
will here in after be called the "absolute system," and the latter,
the "design-center system."
In the absolute system,* the maximum ratings shown for each type
thus rated are limiting values above which the serviceability of the tube may
be impaired from the viewpoint of life and satisfactory performance. Therefore,
in order not to exceed these absolute ratings, the equipment designer has the
responsibility of determining an average design value for each rating below
the absolute value of that rating by an amount such that the absolute values
will never be exceeded under any usual condition of supply-voltage variation,
load variation, or manufacturing variation in the equipment itself.
The equipment should be designed to operate the filament or heater of
each tube type at rated normal value for full-load operating conditions under
average voltage-supply conditions. Variations from this normal value due to
voltage-supply fluctuation or other causes, should not exceed ± 5 per cent
unless otherwise specified by the tube manufacturer.
In the design-center system** adopted by the receiving-tube
industry late In 1939, the maximum ratings shown for each type thus rated are
working design-center maximums. The basic purpose underlying this system is to
provide satisfactory average performance in the greatest number of equipments
on the premise that they will not be adjusted to local power-supply conditions
at time of installation. In the setting up of design-center ratings,
consideration has been given to three important kinds of power supply commonly
in use, i.e., a-c and d-c power lines, storage battery with connected charger,
and dry batteries.
In the case of a-c or d-c power lines, the maximum ratings for tubes
rated according to the design-center system have been chosen so that the tubes
will give satisfactory performance at these maximum ratings in equipment
operated from powerline supplies whose normal voltage including normal
variations fall within ± 10 per cent of a specified center value. In other
words, it is basic to the design-center system of ratings for tubes operated
from power-line supplies that filaments or heaters as well as positive- and
negative-potential electrodes may have to operate at voltages differing as
much as ± 10 per cent from their rated values. It also recognizes that
equipment may occasionally be used on power-line supplies outside the normal
range, but since such extreme cases are the exception, they should be handled
by adjustment made locally.
The choice of ± 10 per cent takes care of voltage differences in
power lines in the
In the case of storage-battery-with-charger supply or similar supplies,
the normal battery-voltage fluctuation may be as much as 35 per cent or more.
This fluctuation imposes severe operating conditions on tubes. Under these
conditions, latitude for operation of tubes is provided for by the stipulation
that only 90 per cent of the design-center maximum values of plate voltages,
screen-supply voltages, dissipations, and rectifier output currents is never
exceeded for a terminal potential at the battery source of 2.2 volts per cell.
While a tube's operating voltages in this service will at times exceed the
maximum values, satisfactory performance with probable sacrifice in life will
In the cases of dry-battery supply and rectified a-c supply for 1.4-volt
tubes, recommended design practice is given in RMA Standard M8-210.
RMA Standard M8-210 (Jan. 8, 1940 Rev. 11-40) is reproduced here for the
convenient reference of design engineers with permission of the Engineering
Department of the Radio Manufacturers Association. Although worded to cover
only receiving tubes, it can be applied to any tube having
* * *
It shall be standard to interpret the ratings on receiving types of tubes
according to the following conditions:
1. CATHODE--The heater or filament voltage is
given as a normal value unless otherwise stated. This means that transformers
or resistances in the heater or filament circuit should be designed to operate
the heater or filament at rated value for full-load operating conditions under
average supply-voltage conditions. A reasonable amount of leeway is
incorporated in the cathode design so that moderate fluctuations of heater or
filament voltage downward will not cause marked falling off in response; also,
moderate voltage fluctuations upward will not reduce the life of the cathode
to an unsatisfactory degree.
2. POSITIVE POTENTIAL ELECTRODES--
The power sources for the operation of radio equipment are subject to
variations in their terminal potential. Consequently, the maximum ratings
shown on the tube-type data sheets have been established for certain Design
Center Voltages which experience has shown to be representative. The Design
Center Voltages to be used for the various power supplies together with other
rating considerations are as given below:
A. AC or DC Power Line Service in
B. Storage-Battery Service-- When
storage-battery equipment is operated without a charger, it should be designed
so that the published maximum values of plate voltages, screen-supply
voltages, dissipations, and rectifier output currents are never exceeded for a
terminal potential at the battery source of 2.0 volts per cell. When storage
battery equipment is operated with a charger, it should be designed so that
90% of the same maximum values is never exceeded for a terminal potential at
the battery source of 2.2 volts.
D. Other Considerations
a. Class A1, Amplifiers-- The maximum plate dissipation
occurs at the "Zero-Signal" condition. The maximum screen
dissipation usually occurs at the condition where the peak-input signal
voltage is equal to the bias voltage.
b. Class B Amplifiers-- The maximum plate dissipation
theoretically occurs at approximately 63% of the "Maximum-Signal"
condition, but practically may occur at any signal voltage value.
c. Converters-- The maximum plate dissipation occurs
at the "Zero-Signal" condition and the frequency at which the
oscillator-developed bias is a minimum. The screen dissipation for any
reasonable variation in signal voltage must never exceed the rated value by
more than 10%.
d. Screen Ratings-- When the screen voltage is supplied
through a series voltage-dropping resistor, the maximum screen voltage rating
may be exceeded, provided the maximum screen dissipation rating is not
exceeded at any signal condition, and the maximum screen voltage rating is not
exceeded at the maximum-signal condition. Provided these conditions are
fulfilled, the screen-supply voltage may be as high as, but not above, the
maximum plate voltage rating.
3. TYPICAL OPERATION-- For many receiving tubes, the data
show typical operating conditions in particular services. These typical
operating values are given to show concisely some guiding information for the
use of each type. They are not to be considered as ratings, because the tube
can be used under any suitable conditions within its rating limitations.
"Tubes are for Music, transistors are for TV and electronics in general"