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VACUUM ELECTRONIC COMPONENTS
Establishing the current rating of o Jennings MMC 5000
mmld vacuum capacitor using the J7002 Kilovoltmeter
What is the Current Rating
of a Vacuum Capacitor?
The current ratings of all Jennings vacuum capacitors are established
on our own 75 KW test transmitter at frequencies of 3 to 16 mc.
At least three capacitors of a given type are tested in the plate
circuit of this transmitter. They are mounted in still air, painted with
a temperature indicating paint, and allowed to reach a maximum
temperature of 175° F. -a conservative figure arbitrarily chosen
to give a uniform basis for rating. The current passing through the
capacitor at this temperature is computed from the voltage reading
of a Jennings J1002 VTVM, which is a peak reading kilovoltmeter
that reads directly through a frequency range of 20 cps to 50 mc.
The maximum allowable operating temperature is much higher than
175° F. and is different for each capacitor.
Current ratings established in this manner can be doublec by the
use of forced air cooling and at least quadrupled by water cooling.
We invite you to send for a recently published catalog
summary describing all of our vacuum capacitors, vacuum
switches, and high voltage measuring equipment.
IENNINGS RADIO MANUFACTURING CORP: 970 McLAUCHLIN AVE. P.O. BOX 1278 SAN JOSE 8, CALIF.
(Continued from page 187)
dividual cycles of subcarrier relative
to the pulse position tends to
confuse any judgment of symmetry.
If the subcarrier lock -in is
de- activated for the purpose of the
test, however, a smooth and complete
envelope of the chroma -signal
transient response will become
distinctly apparent.
The choice of an optimum signal
configuration for this test
method can be determined within
narrow limits by a few elementary
considerations. The amplitudes of
the chroma subcarrier envelopes
(both I and Q components) and
luminance (Y)
pulse should be
roughly equal and of adequate
level. In addition, it is desirable
that the pr i m a r y components
(RGB) be formed simply by resistance
matrixing of pulses of
identical polarity to alleviate any
suspicion of delay differentials in
the special color bar signal
source. These conditions are met
by using a red -magenta background
color field with the red
and blue components proportioned
to produce equal values of I and
Q. An oscillogram of the primary
component waveforms is shown in
Fig. 1 and the resultant encoder
output is illustrated in Fig. 2.
The Unibar Generator
The circuitry needed to generate
these waveforms is simple in
nature. The three primary pulse
signals are derived from only two
pulses, a wide one to define the
limits of the color field and a
narrow one for the gray bar. Inasmuch
as the pattern is intended
for oscilloscope examination only,
there is no necessity for provision
of vertical rate blanking.
avoiding one of the complications
of generating color -bar patterns
for monitor display or systems
transmission.
A circuit using seven d u a l
triodes satisfies this requirement.
A block diagram is given in Fig.
3, above. Adjustments are provided
for width and delay of both
pulses, as well as balancing controls
for level equalization to
eliminate all chroma in the gray
188 For product information, use inquiry card on pages 209.210. Tele -Tech & ELECTRONIC INDUSTRIES June 1956