Push Pull Triodes for Class C

Posted on Feb 4, 2014

The purpose of this document is to answer the question of why things are done in a certain way and why certain components are used instead of others. The circuit below is a representation drawing to be used for explanation, but with some refinement could be a working Class C - Transmitter. After the general explanation more drawings will be shown

Push Pull Triodes for Class C
Click here to download the full size of the above Circuit.

as refinement for a finished product. Please note that the GIF drawings lose some of their detail if shown reduced on screen. You may click on the drawings to show them in a new window and save them for printing. The link coil of L1 is the input for RF excitation. L1 (known as the grid tank coil) is an air core coil with a center tap on the main coil and a link of a few turns iswound over the top center of the main coil. Because of the tight magnetic coupling to the main grid coil, it is generally not necessary to tune the link separately; however a series or parallel tuning capacitor can be placed on the link if it is desired to produce a specific load resistance to the driving stage that may be more critical of SWR. A small antenna tuner may be used between stages for this purpose. The center tap is not used as an electronic balancing point but instead it is used to provide a grid leak path connection point. At the center of a balanced tank circuit, there is very low RF voltage so it is an ideal point to insert the DC connection of grid leak path. The balancing of the circuit is accomplished by having equal capacitances from each end of the the main coil to chassis ground. The grid tuning capacitor C1a and C1b provide this balance. It is very important that the "split stator" as it is called, be a balanced capacitor. It must maintain its balance across the tuning range, from minimum to maximum capacitance. The RF voltage...

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