Downloaded from https://www.everyspec.com MIL-STD-1311D EMISSION CURRENT 1. Emission. To avoid damaging the TUT, the emission voltage shall be applied only for sufficient time to permit the emission to reach the specified minimum value. The duration of the test shall not exceed 5 seconds. When only a minimum current limit is specified, a voltage less than the value specified may be applied provided the required minimum emission current is thus obtained.
In qualification testing of receiving tubes, when only a minimum current limit is specified, the test shall be performed by increasing the applied voltage until the specified minimum emission current is obtained and reading the voltage drop across the TUT. 1.1 Emission at reduced filament voltage. If an emission-current test is specified at reduced filament voltage, this test shall be performed prior to the emission-current test at rated filament voltage. Operate the tube with 90 percent of rated filament voltage only applied. After allowing the cathode temperature to stabilize, apply the emission voltage in the manner specified in 1 above. 1.2 Emission at rated filament voltage.
Operate the tube with rated filament voltage only applied. After allowing the cathode temperature to stabilize, apply the emission voltage in the manner specified in 1 above. 2. Peak emission by voltage drop. The tube shall be tested with the specified voltage applied to the filament or heater, with a 60 Hz anode supply sufficient to start the tube and sufficient series resistance to limit the anode current to the specified maximum current (ib) value per anode. A suitable circuit designed to permit the conduction of the specified peak current for one or two approximate half-cycles per second shall be provided.
The slow pulse repetition is employed to prevent excessive reduction of the tube voltage drop due to cathode heating during conduction. The peak voltage drop, exclusive of the starting voltage measured from an anode to the reference point as shown on a cathode-ray oscilloscope, or by other suitable means, shall be within the limit(s) specified. 3. Peak emission. The filament or heater potential shall be applied and the grid or grids, if present, shall be connected to the anode. A suitable capacitor shall be discharged through the tube and a load resistor. The peak current shall be measured by an oscilloscope suitably calibrated. An equivalent method may be used.
Pulses shall be applied in such a manner that the tube will not be damaged. The peak current shall be within the limit(s) specified and there shall be no evidence of sparking during the test. 4. Emission by oscillation. At the end of the power-oscillation test, the filament potential shall be reduced until the rf power output has been reduced 10 percent, at which point the filament potential shall not exceed the value specified; or the filament potential shall be adjusted to the limit value specified, at which point the power output shall be not less than 90 percent of the initial value. 5. Pulsing emission.
Either of the following test methods may be used to accomplish pulsing emission testing. Previous TSS's that specify pulsing emission or pulsing emission sinusoid may now be interpreted to include either of the a and b options below: a. Square wave. The tube shall be operated at the electrode potentials specified. Where pulse voltages are indicated, the pulse duration shall be not less than 2 nor greater than 10 µ s. Time of rise shall be not greater than 10 percent of the pulse duration and time constant of fall not greater than 20 percent of the pulse duration. The duty shall be not less than 0.001.
Variations in 80 percent of the top portion of the pulse shall not exceed ± 5 percent of the maximum amplitude and no portion shall fall below the maximum amplitude by more than 10 percent. There shall be no sign of arcing during the latter half of the test and the average peak anode current shall be within the limit(s) specified. b. Sinusoidal. The tube shall be operated as a diode at the electrode potentials and conditions specified on the TSS. Apply a nominal 50 percent sinusoidal pulse source which meets the following requirements: Pulse duration (tp) = 2 µ s minimum, 10 µ s maximum, at the base line of the pulse; pulse repetition rate (prr) shall be not less than 20 pulses per second.
There shall be no sign of arcing during the latter half of the test. Excluding any spike, the peak diode current, or peak tube drop (whichever is specified), shall meet the specified limit(s) at the required peak pulse value, when a stabilized reading is obtained up to a maximum of 1 minute. 6. Thyratron or gas-rectifier emission. The tube shall conduct pulses at a recurrent rate of not less than 1 nor more than 60 pulses per second. The duration of the pulses shall be such that the current flows not less than 0.5 nor more than 2.0 percent of the time. The pulse width in no case shall be less than 150 µ s.
The shape of these pulses shall be such that the current rises smoothly and continuously to its peak value near the middle of the pulse. The grid or grids, if any, shall be connected as specified. With the filamentary types, connection to the filament circuit shall be made to the midpoint of the filament transformer. Variations in the tube voltage drop at current values below the peak current specified shall be ignored. There shall be no evidence of sparking of the filament (or cathode) during the test, and the peak voltage drop shall be within the limit(s) specified. METHOD 1231A METHOD 1231A 1231-1 28 March 1975