ULTRA-HIGH-FREQUENCY POWER AMPLIFIER 13 



such that a break from conventional design was inevitable, leaving for 

 future work the satisfactory coverage of the transition region. Since 

 triodes had already been studied as oscillators it was decided to design 

 and construct a pentode. A tentative rating of fifteen watts anode 

 dissipation (per tube) with an operating range up to 300 megacycles 

 was chosen. It was further thought desirable to limit the sum of the 

 grid-to-ground and plate-to-ground capacitances to a value less than 

 eight micromicrofarads in order to facilitate the design of the accom- 

 panying circuits. 



Preliminary considerations led to the conclusion that the desired 

 results could be best obtained by push-pull operation. In view of the 

 required shortness of leads it seemed logical, if not essential, to inclose 

 both sets of tube elements within one envelope and to provide an 

 internal by-pass condenser between the screen and suppressor grids. 

 It also appeared desirable to design the structure so that a simple ex- 

 tension of the screen-grid element would form a partition separating the 

 input portion of the tube from the output portion. By mounting the 

 tube so that the internal partition forms a continuation of the external 

 partition separating the input and output circuits, quite adequate 

 shielding should be possible. From previous experience, it was con- 

 cluded that the special frequency requirements for a 300-megacycle 

 amplifying tube would be satisfied by a design patterned after a 600- 

 megacycle oscillator tube.^ 



To summarize, the following construction features were considered 

 desirable : 



(1) The mounting of two sets of elements in the same envelope. 



(2) A method of interconnecting the two screen grids by a low im- 



pedance conductor. 



(3) A method of grounding the screen and suppressor grids inside the 



tube envelope. 



(4) Complete shielding between input and output sides of the tube. 



(5) The use of extremely short leads. 



(6) Means for maintaining very small spacings between the elements. 



(7) Provision for adequate cooling of all grids. 



(8) Adequate insulation paths to permit a high anode potential. 



(9) The absence of any leads common to both input and output 



circuits. 



The first of the experimental tubes designed to have a fifteen-watt 

 dissipation per anode is shown in Fig. 1. It will be noted that a parti- 

 tion divides the envelope into two parts. This partition is in reality 

 double, being made up of two sheets, one being connected to the sup- 



