Downloaded from https://www.everyspec.com MIL-STD-1311D GRID CURRENTS 1. Total grid current. When the specified voltages applied to the tube, the total grid current read with a series microammeter shall be within the limit(s) specified. The total external circuit resistance shall not exceed 100,000 ohms, except that when the maximum current limit is -0.5 µ A dc or less, the resistance may be increased to 1.0 Meg maximum.
The duration of this test (including preheating time at specified test conditions, if continuous with the test) shall be 2 minutes unless a greater duration is specified, or, in the case of tubes having a specified maximum grid current of 5 µ A or less, it shall be only long enough to establish a steady value. When a greater duration is required, a test period of 3 minutes shall be permitted if the grid current at the end of this time is stable or no longer rising, and does not exceed the limit(s) specified. On those TSSs where zero is specified as the minimum value, a positive current not exceeding 0.05 µ A dc shall be acceptable. 2. Grid emission.
This test applies to tubes where grid emission is high compared to grid leakage. At the conclusion of the test specified in 1 above, the tube shall be biased to cutoff and the grid current measured immediately. This current shall be considered to be due to leakage and primary emission and shall be within the limit(s) specified. 3. Grid leakage. This test applies to tubes where grid leakage is high compared to grid emission. At the conclusion of the test specified in 1 above, the filament or heater voltage shall be cut off and the grid current measured when the parts have cooled. This current shall be considered to be due to leakage and shall not exceed the limit specified. 4.
Grid current (cold). The filament switch shall be opened until the elements have cooled below visible color. The filament switch shall then be closed and the value of the grid current at the first pause in its rising value shall not exceed the value specified. 5. Gas current. When specified on the TSS, the value of the current determined as specified in 2 above shall be subtracted from the value of the current determined as specified in 1 above. This difference shall be considered the gas current and shall be within the limit(s) specified. 6. Primary grid emission.
By means of suitable rectifiers and a 60-Hz ac source, the grid shall be heated during the positive half cycles, and the primary emission measured during the negative half cycles. The voltage shall be adjusted for the input power or average grid current specified. The primary emission current shall be not greater than the limit(s) specified. All unused elements shall be left floating or grounded as specified on the individual TSS. METHOD 1266A METHOD 1266A 1266-1 28 March 1975