Downloaded from https://www.everyspec.com MIL-STD-1311D 4.10 Phototube test instructions. These tubes shall be tested in a lightproof box containing the specified light source. a. Test enclosures. The lightproof test enclosures shall have suitable light baffles provided to insure that only direct radiation from the light source impinges on the phototube cathode. The beam of light striking the cathode shall have approximately parallel rays which are formed by the screen apertures. An adjustable aperture shall determine the area of the cathode subjected to the light bombardment.
The usable areas of phototube cathodes shall exclude support wires or parts falling behind the tube structure such as the stem, but shall not exclude that part of the cathode behind the anode, anode support wire, or activator support wire. Dimensions shall be relative to the bottom of the base shell or end cap. Cathode location shall be by projection to a plane normal to the direction of illumination. b. Test temperatures. The tube shall be placed in an enclosure and a thermometer shall be used to measure the ambient temperature. The temperature of the enclosure shall be controlled by means of a rheostat and adjusted to the specified ambient value.
Infrared radiation from the heating element shall not strike the cathode of the phototube being tested. c. Standardized light sources (LS1). A coiled tungsten lamp with a lead- or lime-glass envelope operated at a color temperature of 2,856 ° K ± 20 ° K shall be used. Nonfiltered light flux on the phototube shall never exceed 0.1 lumen. d. Measurement of light intensity. The distance from the light source to the phototube shall be varied to obtain the desired intensity of illumination measured in lumens. The following method shall be used to calibrate the phototube-test set:
(1) A standard lamp shall be certified periodically at a recognized certification laboratory for candlepower and current requirements at a color temperature of 2,856 ° K ± 20 ° K. (2) The phototube test lamp shall be adjusted to operate at a color temperature of 2,856 ° K ± 20 ° K by means of comparison with the standard lamp through the use of an optical pyrometer. (3) A suitable light-sensitive device shall be calibrated against the standard lamp by calculation.
A phototube-test lamp shall be substituted for the standard lamp and with the calibrated light-sensitive device in the position which the test phototube will occupy in the enclosure, the test lamp shall be moved until the proper light intensity from the lamp falls upon the light sensitive device through the aperture. 4.11 Life-test conditions. The following conditions, when applicable, supplement the conditions on the TSS. a. Unless otherwise specified, the manufacturer may choose intermittent or continuous operation. b.
The mean electrode potentials (except heater or filament) may deviate from the specified values by not more than 10 percent, provided the average electrode dissipations are equal to those obtained under the specified conditions. c. The mean value of the filament or heater voltage shall be maintained at the specified value. d. If a heater cathode potential is required during the life test, the resistance applied in series with this potential shall not exceed 5,000 ohms, except for rectifier types, in which case the series resistance shall be approximately zero. e.
When either ac or dc filament voltage is permitted, the grid bias shall be adjusted so that the average electrode dissipations are equivalent to those obtained under the specified conditions. f. Where a minimum envelope temperature is specified, the requirement will be satisfied if a tube having the applicable characteristic listed below, within the indicated tolerance, is determined to operate at or above the minimum specified temperature at any position in the life-test rack operating at the specified life-test conditions. (1) Grid controlled vacuum tubes. Anode current, in accordance with normal test conditions, is within ± 5 percent of the bogey value. (2) Rectifiers and diodes.
Tube drop, in accordance with the specified conditions is within ± 10 percent of the bogey value. (3) Regulators and voltage reference tubes. Tube voltage drop at the anode current specified for life test is within ± 3 percent of the bogey value. (4) Other tubes. As specified on the individual TSS. g. Where a control grid circuit resistance is specified by a nominal value, its value shall be not less than 80 percent of this nominal value. 6