Downloaded from https://www.everyspec.com MIL-STD-1311D METHOD 1516 STABILITY LIFE 1. Purpose. The purpose of this test is to determine the stability of specified characteristics during early life. 2. General. This is a test of 2 to 20 hour duration, under specified conditions, preceded and followed by measurements of one or more specified characteristics, and with maximum percentage characteristic change specified for individual tubes. The sampling plan and sample size will be stated on the individual TSS or as specified in MIL-PRF-1, section 4. 3. Procedure. a. Serially number all the tubes of the sample. b.
Record the specified characteristic measurements on the entire sample after maximum operation of 15 minutes under specified voltage and current conditions. c. The regular stability-life-test sample shall be operated at the specified stability-life-test conditions or equivalent, for 20 ± 4 hours with an intermediate down-period reading point at 2 hours ± 30 minutes. (Intermittent or continuous operation may be employed.) The regular stability life-test shall be in effect initially and shall continue in effect until the eligibility criteria for the reduced-hours stability life test have been met. d. Reduced-hour stability-life-test.
(1) Eligibility for reduced-hours stability-life test shall be as follows: No lot failure due to the regular stability-life has occurred in the preceding 5 consecutive lots. (2) Reduced-hours stability-life test shall be conducted for 2 hours ± 30 minutes. Acceptance shall be based on the stability-life test endpoint limit. One lot failing the reduced-hours stability-life test shall result in loss of eligibility for the reduced hours stability-life test. (3) The stability-life-test sample from the first lot accepted each month shall continue on stability-life test to the 20 ± 4 hours duration.
Failure of this sample to meet the regular stability-life test endpoint limit shall result in loss of eligibility for the reduced hours stability-life test. e. Life-test conditions shall be conducted as specified in 4.11 (General requirements), except that the mean electrode potentials (except heater or filament) may be established at values differing by not more than 5 percent from the specified values, provided the same average electrode dissipations are obtained that occur with the specified voltages. Fluctuations of all voltages, including heater or filament voltage, shall be as small as practicable. f.
Record measurements of the specified characteristics at the specified reading periods. The measurements shall be taken immediately following the specified reading periods, or the tubes shall be preheated a maximum of 15 minutes under specified voltage and current conditions, and the characteristics immediately measured following the specified reading periods. g. A defective shall be defined as a tube having a change in the specified characteristic greater than that specified. h. A resubmitted lot shall be subjected to all conformance inspection part 1 and part 2 tests, except the following:
Vibration tests Shock tests Physical (including dimensions) Secureness of base, cap, or insert Lead fatigue Barometric pressure, reduced Base strain (miniature) Glass strain METHOD 1516 1516-1 19 April 1968