scope:

This specification covers the general requirements for heat dissipating electron tube shields and associated retainer (bases), and adapters for use in electronic equipment (see 6.1).

This appendix covers the instrumented tubes for use in the heat dissipation tests specified in 4.5.7. The tube type recommended to represent each bulb type was chosen for its high power dissipation. The tube types are listed in table III

A temperature sensitive paint shall be applied to the tube envelope. The appropriate value paint shall be determined by trial and error to provide an accurate indication of the hot spot location when the tube is operated at or near its maximum power dissipation rating and the hot spot is located by visual observation.

The tube envelope diameter shall be measured with a micrometer and recorded. The tube shall be prepared for grooving by masking the entire bulb with masking tape, leaving only a 1/16 inch ±1/64 inch strip uncovered, running lengthwise along the bulb, and through the hot spot. The upper end of the bare strip shall stop ⅛-inch to 3/16-inch from the beginning of the curved shoulder at the top of the tube. The bare strip shall be allowed to run out at the bottom of the tube.

A sand blaster with a ¼ to ½-inch-diameter nozzle may be used. The etching material may be No. 120 or 220 grit aluminum oxide powder. Air pressure may be 45 psi. The nozzle may be positioned 4-inches from the tube surface, so that the etching powder will impinge at right angles to the surface to be etched.

Approximately 25 to 50 passes may be required with the nozzle over the exposed glass. Each pass shall be extended beyond both ends of the tube envelope to prevent overetching at the ends of the groove. On the 6336A tube, it may be necessary to roughen (by sandblasting) a small surface area, delta in shape, at the lower end of the groove on the outside of the glass, to serve as a better anchor for the thermocouple and protective tube.

The depth of the groove shall be 0.010-inch + .003-inch, −.001-inch. Periodic measurements of groove depth shall be made, as the speed of etching will vary with the cleanliness, age, and moisture content of the etching material.

The thermocouple used shall be a welded junction of 36 gage iron and constantan wire. The thermocouple shall be laid into the groove with its junction on the hot spot of the tube, held down with a spring or other means and the leads running out of the lower end of the groove. The groove shall be filled with Sauerisen, Insa-lute #1 cement, or equivalent, and the cement allowed to dry at 100°C for 24 hours or 36 to 48 hours at room temperature. The excess shall then be scraped off to restore the original contour of the tube envelope.

intended Use: