Downloaded from https://www.everyspec.com MIL-STD-1311D METHOD 1201C SHORT AND DISCONTINUITY DETECTION Requirements. When this method is specified on the TSS, testing shall include the following tests: discontinuity, shorts, permanent shorts, tap shorts, and air leaks. Tubes shall be rejected as inoperative, if failing any of these tests. 1. Discontinuity. Tubes shall be tested for discontinuity of any possible circuit, including shell, base, base sleeve, shield, and duplicate-pin connections to the same electrode, as applicable. During the discontinuity tests, the tubes shall be tapped (except life- test samples) as specified in 2.
Tubes shall give no indication of permanent or intermittent open circuits during this test. 2. Shorts. Tubes shall be tested for shorts between any elements, no-connection base pins, and internal shields.
The tube shall be connected to the shorts test equipment in such a manner that the minimum specified sensitivity specified herein is maintained between all elements in a single section of the tube, but like elements in the sections of a multisection tube may be paralleled, provided that the mechanical assembly of the tube structure is such that the possibility of shorts between sections is proven to be remote in that the cumulative results of tests on 1,000 or more tubes of a given construction shows that no more than 0.4 percent of the tubes show any indication of tap shorts between like elements in the sections of a multielement tube.
The shorts simulator used for calibration shall be of the passive type (time-controlled-switch closure) and shall add a minimum of capacitance to the circuit under test consistent with good low-capacitance wiring technique. Except for heater-cathode, a short circuit shall be defined as an equivalent resistance between adjacent elements which persists for a period of time in excess of that determined by a limiting curve of resistance versus time duration passing through the following points:
Resistance (ohms) Time duration 600,000 - - - - - - - - - - - - - - 500,000 - - - - - - - - - - - - - - 100,000 - - - - - - - - - - - - - - 1,000 - - - - - - - - - - - - - - Constant value (permanent short) 500 µ s 100 µ s 60 µ s For heater-cathode, the sensitivity need not exceed 10 percent of the above resistance value. Figure 1201-1 illustrates this curve and is marked to show the area of rejection and acceptance; for example, a short circuit of 100,000 ohms equivalent resistance shall be accepted if it persists for less than 100 µ s, etc. The voltage applied between adjacent elements of the tube shall have a value between 20 and 70 volts dc or peak ac. 2.1 Permanent shorts.
Tubes shall be tested without mechanical excitation. 2.2 Tap shorts. Tapping procedure for receiving tubes. a. The tube shall be mounted in the test socket of the shorts test equipment and tapped three times on each of two planes 90 degrees to 120 degrees apart. During tapping, the tube shall be supported only by a socket and a light-finger pressure or soft-cushioned mechanical pressure on the dome of the bulb. The finger or mechanical pressure on the dome of the bulb shall be used only to prevent the tube from coming out of the socket. This pressure shall be so applied that it offers negligible restraint to lateral motion at the top of the bulb. b.
The tap blows shall be delivered to the tube approximately two-thirds up on the holddown height. c. The tapping device shall be so designed and adjusted that it will deliver an impulse of approximately one-half sine wave of 300 ± 50 µ s duration, as measured at 10 percent of the amplitude of the half wave and have a minimum average amplitude equivalent to 80 G peak acceleration for T5-1/2 and larger tubes, and 40 G peak acceleration, for directly heated filamentary T5-1/2 tubes intended for dry-battery operation, and for tubes smaller than the T5-1/2 bulb size. d.
The tapper impulse shall be measured with a Gulton model A-305 accelerometer, or equivalent, mounted in a standard production type (replaceable cap and clips) T5-1/2 socket and having no other support. For this measurement, the TUT shall be removed from the socket and the test accelerometer shall be inserted. The tap blow shall be delivered to the accelerometer at the approximate midpoint and in a direction parallel to the plane of maximum sensitivity of the accelerometer. The output of the accelerometer shall be coupled through a cathode follower and low-pass filter-amplifier combination to a suitable calibrated oscilloscope.
The low-pass filter shall have a minimum high frequency cutoff at 5,000 Hz. (The Gulton KA-1 test set on 5 kHz filter position possesses appropriate characteristics.) 2.2.1 Reliable tube types. If a short indication is obtained at any time during the tapping procedure, the tube shall be rejected as inoperative. METHOD 1201C 1201-1 28 March 1975