Downloaded from https://www.everyspec.com MIL-STD-1311D 7.1 Receiving tubes. Receiving tubes shall be tested in accordance with 7 above, except the frequency range shall be traversed in 1 minute (minimum), 3 minutes (maximum). The specified voltages shall be applied to the tube during vibration. The value of Eb under test conditions shall be regarded as Ebb and shall be applied to the tube through the specified resistor Rp. The value of the alternating voltage, Ep, produced across the resistor, Rp, as a result of vibration, shall be measured with a suitable device.
This device shall have an appropriate voltage range and shall have the ability to indicate with an error of less than 10 percent the rms value of a sine wave at all frequencies as specified below and shall have dynamic response characteristics equivalent to or faster than a VU meter. The voltage Ep shall be capacitance coupled to the measuring system consisting of cables, amplifier, low-pass filter, and indicator. Input impedance of the measuring system shall have a minimum value of at least 10 times the resistor, Rp, at 10,000 Hz.
Combined frequency response from the capacitor input through the amplifier and filter shall be flat within ± 1 dB from 50 to 10,000 Hz, as referenced at 1,000 Hz shall be down 10 ± 2 dB at 15,000 Hz, and down 20 ± 3 dB at 20,000 Hz. The impedance of the anode and screen voltage supplies shall not exceed that of a 40 µ F capacitor at 10 Hz. 7.1.1 Value of Ep. The value of Ep shall not exceed the limit specified at any point in the sweep-frequency range nor shall this test result in open circuits, permanent shorts, or tap shorts. 7.2 Sweep-frequency-vibration fatigue (destructive test).
The tubes shall be fastened rigidly to the vibration platform and vibrated with simple harmonic motion over a frequency range of 50 to 2,000 Hz at a peak acceleration value of 10 G. The acceleration over the frequency range shall be within ± 25 percent of the referenced acceleration at 50 Hz. The frequency of vibration shall be varied from 50 to 2,000 Hz and back to 50 Hz with the period of the sweep cycle being 10 minutes minimum to 20 minutes maximum. The tubes shall be vibrated for a total of 6 hours, that is, 2 hours in each of three axes, X, Y, and Z. For special-construction tubes, vibration position shall be specified on the TSS. Only rated filament or heater voltage shall be applied.
Tubes which show one or more of the following defects shall be considered failures: a. Tubes which show permanent or tap shorts or open circuits following sweep-frequency-fatigue test. b. Tubes which do not comply with sweep-frequency-vibration-fatigue test end point limit(s) as specified on the TSS. 8. Variable-frequency vibration. The tubes shall be vibrated under the conditions specified for low-frequency vibration and axis Z shall be added. The tubes shall be vibrated at a constant amplitude in each of three axes through the frequency range from 10 to 50 Hz and back to 10 Hz. The time for gradually covering the range from 10 to 50 Hz and back to 10 Hz shall be 3 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. The tubes shall not show vibrational output in excess of the maximum limit specified. This test shall not result in tap or permanent interelectrode shorts or defects which cause the tube to be inoperable. 9. Vibration-fatigue test (destructive test).
The tube shall be rigidly mounted on a table vibrating with simple harmonic motion at a frequency of 25 ± 2 Hz with an amplitude of .040 ± .005 inch (total excursion of .080 ± .005 inch) or any equivalent combination of frequency and excursion resulting in 2.5 G applied to the TUT. The tubes shall be vibrated for a total of 96 hours, 32 hours in each of three axes, X, Y, and Z. Only rated filament or heater voltage shall be applied. Tubes which show one or more of the following defects shall be considered failures: a. Tubes which show permanent or tap shorts or open circuits following vibration-fatigue test. b.
Tubes which do not comply with vibration-fatigue test end point limit(s) specified on the TSS. 10. Microwave tubes. The TSS shall specify characteristics to be measured during or after vibration. METHOD 1031A 1031-2 25 March 1970