MIL-PRF-1/1640E
TABLE I. Testing and inspection - Continued.
11/ A missing pulse is defined as one whose energy within ± 1 percent frequency range of the normal operating
frequency is 70 percent or less than that of a normal pulse. The tube shall be considered stable if the missing
pulse limit specified is not exceeded during the vibration time at acceleration levels and durations specified in the
operating vibration test.
12/ The tuner shaft shall be continuously driven at a speed of 85 ± 10 rpm. At the completion of the test, the TUT
shall meet test condition 1 requirements. The backlash shall not exceed 15 MHz. During the test, the tuning
shaft shall not be lubricated. A cycle consists of two complete excursions each in opposite directions through the
tuning range of the TUT. This is a destructive test. Life-test samples may be used.
13/ The ambient temperature of the chamber shall be -55°C. The cooling air supplied to the TUT shall be -55°C at
40 cfm maximum. The temperature of the TUT shall be allowed to stabilize at this ambient temperature for a
minimum of 4 hours. At the conclusion of this exposure period and while at this temperature, heater voltage of
13.75 V shall be applied for a maximum of 150 seconds before application of anode voltage. The stability test
shall be of 3-minute duration and shall begin after 30 seconds of anode operation. The provisions of 14/ shall
apply.
14/ Stability shall be measured in terms of the average number of output pulses missing, expressed as a percentage
of the number of input pulses applied during the period of observation. The missing pulses (MP) due to any
causes, are considered to be missing if the rf energy is less than 70 percent of the normal energy level. The
stability shall be measured when a VSWR of 1.5 minimum is introduced in the load and the phase is adjusted to
produce maximum instability. The missing pulse test shall be counted during any three consecutive minute
intervals of a 6-minute period.
15/ Cooling air shall be applied so that under the conditions of test condition 2, T(body) measured at the point
indicated on figure 1, shall fall between 80°C and 100°C after the thermal equilibrium has been reached. The
TUT may be operated and the airflow preset a minimum of 12 hours before the test. The TUT shall not have
been operated for 12 hours prior to the performance of the frequency change (warm up) test. The test shall be
performed in the following manner: Anode voltage, as specified for test condition 2, shall be applied after a
maximum of 150-seconds heater warm up time. The frequency shall then be measured at approximately 3-
minute intervals until frequency stabilization occurs. A graph of frequency versus time shall be constructed using
the data. The frequency deviation from the stabilization frequency shall not exceed the limit specified herein.
16/ The pushing factor shall be measured in three steps, 4 amperes each (15a to 19a, 19a to 23a, 23a to 27a) and
no value shall exceed the limits specified herein. The peak current through the TUT shall alternately be the limits
as specified under this test condition. These tests shall be run to exclude the effects of thermal drift and
frequency instability not due to pushing.
17/ The rf bandwidth and minor lobe ratio shall be within the limits specified herein when a VSWR of 1.5 minimum is
introduced in the load and the phase is adjusted at the start of each measurement to produce maximum
degradation. A satisfactory spectrum is one whose slope does not change sign more than once for power levels
greater than the specified dB below its peak.
18/ The seal formed by clamping the magnetron mounting plate against a suitable magnetron test fixture shall be
hermetically tight for 1 minute minimum with the air pressure specified herein applied to surround the entire input
bushing below the mounting plate.
19/ The seal formed by clamping the magnetron output flange against a suitable magnetron test fixture shall be
hermetically tight for 1 minute minimum with the air pressure specified herein applied internally to test fixture.
20/ The minimum air pressure to assure prevention of electrical breakdown in the output coupling shall be 15 psia for
VSWR up to 1.5 with phase shift variable over 360 electrical degrees. The TUT shall be coupled directly to
M3922/53-002 (UG-51/U) choke flange in accordance with MIL-DTL-3922/53 modified so that mounting holes
provide clearance for No. 8 bolts.
21/ The modulator shall be such that the energy per pulse delivered to the tube, if arcing occurs, shall not greatly
exceed the normal energy per pulse. The tube heater shall be protected against arcing by use of a connector
that places a minimum of 4,000 pF across the heater directly at the input terminals.
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