MIL-PRF-1/1385K
TABLE I. Testing and inspection - Continued.
The cooling test shall be made as follows: At an ambient temperature of 25°C, both base and anode shall be cooled by
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applying an airflow of; 7580W, 3.8 cfm maximum; 8930, 6.0 cfm maximum; at sea level from a single source using the infinite
baffle system as shown on figure 2, or equivalent. At the specified test conditions, the anode core temperature shall not
exceed the specified limit. Temperature shall be measured by means of a thermocouple, located as follows: The
thermocouple shall be embedded in the top of the anode core, adjacent to the cooler, by means of drilling a small hole,
shallow enough so that the tube vacuum shall not be lost, placing the welded thermocouple junction therein, and then peening
the edges of the hole so as to hold the thermocouple firmly in place. Good electrical continuity between the thermocouple
and the metal area in close proximity shall be demonstrated before the cooling test can be performed.
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An infinite baffle system as shown on figure 2, or equivalent, shall be used. Airflow shall be as follows: Type 7580W, 3.8 cfm
at sea level; Type 8930, 6.0 cfm at sea level. The static pressure drop is measured across the tube and socket, with an air
director (chimney) in place, to direct the total airflow through the anode cooler assembly of the tube under test (TUT).
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During the performance of life test (2), the rf grid driving voltage and the bias voltage shall be monitored and held constant.
The bias voltage shall be adjusted to produce the specified value of Ibo and the rf drive shall be adjusted to produce the
specified anode current of 250 mA dc during an initial adjustment period not to exceed 4 hours. In no case shall the grid be
driven positive with respect to the cathode as indicated by a grid current of 50 µA dc maximum. At the conclusion of the life-
test period, the change in anode current from the initial value (ĆIb), and the power output (Po) shall be noted and the tube
shall meet the listed requirements for these parameters. Prior to the performance of life test (2), the tube shall have met the
requirements of the linear amplifier power output and distortion test. A record shall be kept of the bias voltage used to
produce the specified Ibo and the amplitude of the two-tone driving signal used in the distortion test initially, and when life test
(2) is completed, the third and fifth IM distortion shall again be measured, using this same value of bias voltage (irrespective
of the value of Ibo this voltage may produce) and this same value of drive signal, and the tube shall meet the listed end-point
requirements.
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No other voltages shall be applied except for the test value shown. The test voltage, with the indicated polarity, shall be held
for 30 seconds minimum, with no apparent arcing and a leakage current not to exceed the limit shown (see figure 4).
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Tube type 8930 is produced by using a larger diameter cooler on the basic 7580W tube which has met all the requirements
listed herein. After replacement with the larger cooler, the 8930 tube shall meet the additional requirements as specified
herein.
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The leakage current reading shall be taken during the 3 minutes immediately following the required 2-minute warmup period.
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Circuit and cavity shall be in accordance with Drawing 223-JAN.
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Each TUT shall be subjected to one sweep cycle in each of the three axes X, Y, and Z. The X axis shall be defined as normal
to a plane drawn through base pins No. 1 and 5. The Y axis shall be defined as normal to a plane drawn through base pins
No. 3 and 7. One sweep cycle (28 to 2,000 and return to 28 Hz) shall be covered in 6 to 12 minutes. The specified voltages
shall be applied during the test using the basic test circuit shown on figure 3. Tubes found to electrically oscillate for causes
other than vibration shall not be tested nor rejected on this test. Each tube shall be vibrated for 60 seconds at the frequency
which gives the maximum vibration (noise) output voltage in each of the three axes. If at the end of the 60 seconds the
vibration output voltage is increasing, the vibration shall be continued until there is no further increase. The tubes shall not
show noise-voltage output in excess of the maximum limit specified, except one intermittent short per tube shall be allowable
during this test. In addition to reading noise voltage output on the HP400D, or equivalent, a permanent recording shall be
made using a good-quality recorder to produce a plot of noise voltage versus frequency. Noise-voltage amplifiers used with
the recorder shall have a ± 1 dB frequency response over the range to be measured and the overall recording equipment
shall be capable of fast response in order to show sharp noise voltage spikes resulting from internal tube resonances or other
phenomena. Prominent noise peaks indicated on the recording shall be individually investigated by fixed-frequency
operation, and the 60-second operation shall be made at the frequency of highest noise as so selected. Frequency at the
extremes of the sweep shall be read with an accuracy of ± 1 Hz below 100 Hz and 1 percent above 100Hz.
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The tube shall be subjected to the specified acceleration in the X, Y, and Z axes, with six shocks in each axis. Tubes showing
any permanent shorts, or more than one temporary short during the test, shall be rejected. The applied shock shall be an
approximate half-sine wave motion with duration measured at the zero axis level.
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This test is to be the first test performed at the conclusion of the holding period.
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