Simple. Some would say painfully simple. Well then, let us look at the following circuit. How does it work?

we closely examine the cathode-to-grid voltages on each tube, we see that really nothing has changed, only our perspective, our reference has.
  Perspective is what is needed to understand the workings of the Circular/Bridge/Balanced amplifier and, in fact, all other amplifiers as well. Let us start again with the more conventional amplifier topology that easy to understand because of familiarity. Now let us restring the "necklace."

Strange new amplifier design.

   If this circuit immediately makes sense to you, then you are very mentally limber indeed. If you are still scratching your head, then look at the circuit below.

  Of course, this circuit is obviously just a tube push-pull output stage, as used in the Futterman  type amp-lifier. Well, in fact, this circuit and the preceding one are the same circuit; they are just drawn differently.

  We begin by limiting ourselves to the two voltage sources, the two output tubes, and the speaker; we will also ignore all considerations of input and driver circuitry. Two other ways these parts can be arranged on our electrical "necklace" present themselves. Basically, the load can fall between the cathodes or the plates. In all cases, current flows in a circular path with or without a speaker bridging the outputs. In all cases, one tube can be completely cutoff during a portion of the output  signal, which means that Class A, AB, or even Class C operation is possible.

   Electronics allows more freedom than most imagine. As long as the implied functionality remains the same, we are free to draw the circuit as we please. (A friend once proudly showed me a circuit board he had made. I thought it was a great gag and laughed loudly. He did not see the joke. His board was a literal redrawing of a published schematic: each part was oriented as it was on the printed page, each line drawn had been duplicated in copper trace, even the dots that symbolized a "connection" were rendered in copper. He was convinced that if a part was drawn perpendicular to another, then, in order for it to work, it must be perpendicularly laid out in reality.) Furthermore, we are free to set ground where we please. A battery can be a positive power supply, if we place ground at the negative terminal; or a negative power supply, if we place it at the positive terminal. Ground is not a component, but the voltage reference point of an amplifier. Thus, if we wish, we can even swap what is normally the output and what is normally ground, as shown below.

  The amplifier at the   right  functions identically to the more conventional one, all appearances to the contrary. The drive volt-ages may seem inverted compared to the more conventional one, but if

< PREVIOUS

NEXT >