MIL-PRF-1/851H
TABLE I. Testing and inspection - Continued.
1/ Prior to the application of high voltage, the cathode shall be heated by applying either 16 volts for 12 minutes (this shall be typical
equipment standby voltage) or 20 volts for 3 minutes (this shall be maximum voltage minimum time condition). On the application of
anode voltage, the heater voltage or current shall be lowered to the specified value.
2/ This shall be the maximum instantaneous surge current. There shall be a suitable series impedance during starting time to limit
surge current to this value. The cold resistance of the heater is approximately 0.5 ohm.
3/ The input circuit shall be designed so that the energy per pulse delivered to the tube, if arcing occurs, cannot greatly exceed the
normal energy per pulse. Modulators of the discharging network type may satisfy this requirement. The total input capacitance of
the tube and circuit shall be 15 pF minimum.
4/ The temperature shall be measured at the points indicated on figure 2.
5/ Life-test cycle. Ten minutes at no voltage, 3 minutes at Ef = 20 V 400 Hz, 7 minutes at Ef = 16 V 400 Hz, 20 minutes at test
condition 5, 20 minutes at test condition 6, σ' = 1.5 ± 5 percent with phase varied through 180° at least five times during the pulsing
part of the hourly cycle. Frequency shall be changed at the rate of approximately 100 MHz per hour, either continuously or in steps.
t shall also include all time during which the heater is operating.
6/ After application of heater voltage for the required warmup time, apply a pulse voltage with the rise characteristics specified in the
test conditions and increase slowly (within 15 seconds) to the value of Ib required. Unless otherwise specified, VSWR of the load
shall be less than 1.05. In power output (1), the tube should attain the specified minimum power output within 5 minutes after high
voltage is applied.
7/
The rate of rise of voltage (rrv) shall be expressed in kilovolts per microsecond, defined as the steepest tangent to the leading edge
of the voltage pulse above 80 percent amplitude when amplitude is defined as a horizontal line drawn tangent to the top of the
smooth peak.
The duty cycle shall be obtained by applying pairs of pulses separated from each other by a value of 15 ± 1 µs, with alternate pulses
8/
occurring at a nominal repetition rate of 2,000 pulses per second (pps). This is comparable to a combined repetition rate of 4,000
pps.
9/
When observed on a spectrum analyzer, a suitable spectrum is considered one in which the major lobe has a shape such that its
slope does not change sign more than once for power levels greater than the minor lobe value specified herein. This shall be
expressed as the difference in power levels in terms of dB.
10/ This test shall be made with the magnetron tuned to an operational frequency of 9,600 MHz. The phase of maximum loading to be
coupled to the magnetron output shall be determined by the distance from the output flange at which a standing wave ratio minimum
can occur, expressed in terms of a fraction of wavelength in the guide (λg).
11/ With pressure of 30 psia applied at the waveguide output, internal-to-external leak rate shall not exceed 0.1 cubic inch per minute.
12/ Requirements shall be satisfied over the entire tuning range. Radio-frequency bandwidth, stability (1) and (2), backlash, and
spectrum shape tests may be done at 100 MHz intervals over the range from 8.5 to 9.6 GHz.
13/ 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. Missing pulses (MP), including those due both to arcing and moding, shall be
considered to be missing if the rf energy is less than the percentage specified herein of the normal pulse energy level at the
specified frequency. Test shall be performed under least stable conditions of phase of load and frequency for any 5 minute
maximum period of a 30-minute period.
14/ The reading of the tuning dial at 9,500 MHz is designated as g1. The frequency at other tuning settings as indicated in the symbol
column (g1 + dial turns) shall be as specified, always setting tuner readings by tuning toward higher frequencies. Allow 5 minutes
for tube to reach equilibrium after a frequency change.
15/ Tuning mechanism shall be smoothly operable throughout entire mechanical tuning range with torque of 6 inch-ounces maximum
applied to tuning shaft.
16/ Stability (2) shall follow stability (1).
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