MIL-PRF-1/1679C
TABLE I. Testing and inspection - Continued.
5/ The tube under test (TUT) shall be vibrated (simple harmonic motion) with an ascending sweep only. Each tube
shall be vibrated in the X, Y, and Z axes, under the specified conditions. The impedance of the anode and
screen voltage supplies shall not exceed that of a 40 µF capacitor at 10 Hz. The value of the alternating voltage
(Ep) produced across the resistor (Rp) shall be measured with a suitable device. This device shall have an
appropriate voltage range and shall have the ability to measure, with an error of less than 10 percent, the rms
value of a sine wave of voltage at all frequencies from 20 to 5,000 Hz. Thermal or VU meters may be used
provided the shunting effect on the anode load does not result in an error greater than the 10 percent allowed
above. The time for covering the sweep range of 10 to 50 Hz shall be 3 minutes minimum, with the time for
covering the range of 10 to 200 Hz being 4 to 15 minutes. Each tube shall be vibrated for 60 seconds at the
frequency which gives the maximum vibration output voltage in each of the three axes. If at the end of 60
seconds, the vibration output is increasing, the vibration shall be continued until there is no further increase.
6/ The tests listed below shall be the first tests performed after the holding period in the following order:
First:
Peak emission
Second: Total grid current
Third:
Grid-pulse operation (1)
7/ The TUT shall be shocked in the X, Y, and Z axes, with six blows in each axis. An approved short tester shall be
used to indicate any shorts between the cathode and control grid and between the control grid and screen grid.
No permanent shorts or temporary shorts are allowed during the test. The applied shock shall be an
approximate half-sine motion, with duration measured at the zero axis level.
8/ During life test, any tubes which will kick out the overcurrent relay one time or more in any 24-hour period shall
be considered a failure, excluding an initial stabilization period of 15 minutes.
9/ Heater voltage shall be cycled approximately 5 minutes "on" and 25 minutes "off". No grid-cathode shorts are
permitted during or after life test. The specified minimum t = 500 hours includes 1,000 complete "on-off" cycles.
For qualification, data on a sample of 10 tubes shall be submitted.
10/ Primary-grid-emission tests shall be made in a circuit with suitable rectifiers and resistors, to limit the voltage
applied to the grid under test during the heating half-cycles, while allowing the emission measurement to be
made at 110 volts rms for the control grid and 750 volts rms for the screen grid during the measuring half-cycles.
11/ In all cases of operation with ambient temperature above 25°C, above sea level, poor ventilation, or a
combination of these factors, a heat dissipating connector is allowable on the anode terminal cap. Adequate
ventilation may be provided and the maximum temperature rating for envelope and seals shall not be exceeded.
12/ Test to be performed every three months, utilizing an accept on zero defect sampling plan.
13/ With qualifying activity approval as an alternative to stand-alone life test equipment setup, life testing may be
conducted within an application system that simulates the test conditions and durations, or equivalent. The
application system life-test procedure must be approved by the qualifying activity. Application system life-test
report, including data, life-test endpoint test data, and results summary, must be supplied to the qualifying activity
for acceptance, recording and storage.
14/ With qualifying activity approval in each case, the manufacturer may provide, in accordance with MIL-PRF-1,
service-life guarantee, in lieu of performing life testing. Life test endpoints specified shall apply to service-life
guarantee conformance as well as to life test conformance. The number of hours of system-deployed,
accumulated tube-operating time shall be approved by the qualifying activity and be a minimum of 500 hours.
Service-life guarantee shall define tube operating life and not time from purchase or delivery. Tubes sold under
service-life guarantee shall be marked with contract number and with the number of tube operating hours
guaranteed. The qualifying activity may restore life testing requirements when service performance or tube
reliability indicates it is justified.
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