ULTRA-HIGH-FREQUENCY POWER AMPLIFIER 15 



The Ultra-High-Frequency Double Pentode Tube 



The successful operation of the experimental models described above 

 indicated the desirability of continuing this line of attack. A complete 

 mechanical redesign to facilitate the fabrication and pumping was 

 undertaken. Fig. 3 is a photograph of this design. Section views 

 are shown in Fig. 4. The large capacitance between the screen and 

 suppressor which characterized previous models was retained in the 

 form of concentric cylinders instead of parallel plates. These cylinders 

 and the flange at one end effectively shield the input and output sides 

 of the tube. The low impedance connection between the two screens 

 provided by these cylinders is an important feature of the design. 

 Adequate cooling of the screen grid is provided by mounting it directly 



Fig. 3 — The ultra-high-frequency double pentode vacuum tube. 



in a slot in one of the cylinders. The control grids are of the so-called 

 fin type of construction already employed with considerable success in 

 triode oscillators. They consist of a series of tungsten loops attached 

 to a common cooling fin. This construction makes feasible the use of 

 extremely small dimensions, so that the grid-filament spacing is com- 

 parable with the filament diameter. One of these grids is illustrated 

 in Fig. 5. The length of leads has been kept as small as is consistent 

 with mechanical requirements. The longest lead, measured from the 

 mid-point of its attached element to the outside of the envelope, is 

 about three centimeters. Other details of the design are evident 

 from the photograph and the diagram. 



Operating characteristics and constants are listed in Table I. 



Special attention is directed to the values of interelectrode capaci- 

 tances and lead inductances. It will be observed that while the inter- 



