TUBE FOR PULSE CODE MODULATION 51 



are sealed in at opposite ends of the tube envelope. The over-all length of 

 the tube is UJ'' with a maximum bulb diameter of 2Y\ 



The electron gun operates at a final anode potential of 1000 volts with a 

 beam current of approximately 10 microamperes. A potential of about 100 

 volts applied to the signal input deflection plates deflects the beam from the 

 center to the top of the aperture plate. This corresponds to a maximum 

 deflection angle of 10^°. 



The four electrodes of the target assembly, secondary collector, quantizing 

 grid, aperture plate and output plate are shown in the photograph of Fig. 5 

 from bottom to top respectively. The secondary collector is a simple rec- 

 tangular shaped electrode. The quantizing grid consists of a circular frame 

 with a parallel array of grid wires stretched across a rectangular opening. 

 The aperture plate is a thin disc with apertures arranged in a binary pattern 

 which provides for a seven-digit code. The output plate is a thin circular 

 disc. Both aperture and output plates are coated with a carbon layer to 

 suppress secondary electron emission from their surfaces. 



The parts of the target assembly are held in accurate alignment in a jig 

 and cemented and held in position on four ceramic rods. The entire as- 

 sembly is held rigidly in the tube envelope by means of spacers attached to 

 the quantizing grid and output plate. 



The target assembly is ahgned with the electron gun and deflection plate 

 axes by means of lineup tools in the glass lathe at the time the final seal is 

 made at the center of the glass envelope. It has been possible to hold the 

 alignment of the deflection axes with the aperture plate to within sHghtly 

 less than 1° with this construction. 



The construction of the quantizing grid may be seen more clearly in the 

 photograph of Fig. 6. The grid frame has raised portions on two sides of 

 the rectangular opening. These are milled with a series of grooves for each 

 grid wire. The grid laterals are affixed in the grooves by brazing and are 

 thus accurately spaced with respect to each other and to assembly lineup 

 holes which can be seen spaced around the edge of the grid frame. 

 The wires are held taut by means of a flat spring which is welded to the 

 grid frame and supplies tension to stretch the lateral wires. The grid wires 

 are 4.0 mils in diameter, processed to have a secondary emission coefficient 

 of about 3. The laterals are spaced 11.6 mils between centers. 



The openings in the aperture plate are made by a punching operation. 

 The area of the aperture plate covered by the first and second digit columns 

 is milled to a thickness of 5 mils in order to facilitate accurate punching of 

 the smallest apertures. The apertures in the first digit column (bottom 

 horizontal row in Fig. 5) are rectangular .012'' x .062''. The seven-digit 

 code pattern provides 128 different output pulse groups. The wide openings 



