consists of the vacuum tube and the primary of the second transformer.
In the second R.F. stage, the source of e.m.f. is the secondary of the second transformer and the load consists of the second tube and the primary of the third transformer. The same is true for each succeeding circuit. In the third stage, the presence of the grid leak, GL, causes the tube to act as a detector which serves to convert the radio frequency current into current of audio frequency and at the same time give it a slight boost. The last stage, the output stage, is shown as a single tube stage but in the complete diagram this is shown as a 2-tube stage, the two tubes being arranged in push-pull.
Go over the complete circuit carefully, Fig. 20, trace each individual circuit through to the best of your ability. Don’t bother about the cathode series resistor in the detector stage or
Fig. 21
the push-pull arrangement as these will be explained in detail later on in the course. Notice that the plate circuit is shown with darker lines than the other circuits which will make it easy for you to trace them through. Just one hint--the question will probably arise in your mind regarding the return conductor of the plate circuit. As it is shown, there is only one conductor, the plate supply--how then can the plate circuit be complete? You remember that when we were considering Fig. 18 it was mentioned that the filament is common to both filament circuit and the plate circuit. Therefore, it should be apparent that there must be some direct connection between the plate circuit and the filament circuit. If you study the supply system shown at the lower right-hand portion of the diagram, you will see that the plate supply is grounded. It is this ground that provides the connection
