This month we tackle the Circular/Balanced/Bridge amplifier again. This time we show where the ground can be placed on the output stage of this amplifier and how even a stereo amplifier could be made out of the circuit, in spite of the popular dictum that the ground must be left floating in relation to the outputs; it doesn't. Once again, I have to admit that I am constantly amazed at the degree to which this circuit is able to shut down the analytical portions of many a tube fancier's brain. Maybe after this month's article, I will get fewer blank stares and pronouncements on how this circuit is something mysterious, radically different from all other amplifiers, defying both reason and math, and that only the chosen few can understand how it works. ("It must be Class A; all the ads say so.")
  John Atwood continues his coverage of regulator with a look at series regulators that use triodes and pentodes as pass devices (and no transistors and no MOSFETs - I know some were beginning to worry that we had allowed too much solid-state to seep into this journal).
   We have made this issue slightly narrower (.25 inches) so that those readers living in Europe and elsewhere can now more easily print this journal on A4 paper stock. If you have had difficulties with printing before, you need to adjust the Page Setup option in your browser. First, click "File" and then "Page Setup" on your browser menu bar and set the left page margin to ½ inch (12mm).
   Remember, if you have a request or suggestion of your own for either an article topic or circuit, please e-mail:

Where to put the ground
   Time again to tackle the Circular/Bridge/Balanced amplifier. Last month we ended with a schematic to ponder; it consisted of 4 triodes, 4 power supplies, 2 speakers, and one ground, as shown below. With independent input and driver circuits, this output circuit arrangement could form the basis of a stereo amplifier.

   After some inspection, it can be seen that really only three power supplies are needed for two output stages.

   Notice that by grounding one cathode, the output tube's drive voltages must now differ in amplitude.

But this situation is no different from the usual totem pole arrangement, where the top tube's grid receives a much larger voltage swing than does the bottom tube, with all grid voltages relative to ground. Not balanced?

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