It's time to stir things up a bit: how about a single-ended amplifier that doesn't look single-ended. Single-ended amplifiers have come in basically three flavors: conventional, parallel, and para-feed. The conventional arrangement is shown below. Consisting of just a few parts, this amplifier is conceptually the easiest to understand. (Of course, "easiest" is relative; many do not understand how, when in use, the plate can swing to a voltage more positive than the B+ voltage.) The para-feed arrangement places the output transformer between the plate and ground and uses a choke to mimic a constant current source. (In fact, a current source can replace the choke at the cost of needing a twofold increase in B+ voltage.) This variation provides a better PSRR figure and allows the use of a non-airgapped output transformer, which means that a nickel core material can be used, furthering the transformer's performance. The parallel arrangement is the conventional arrangement but with multiple output tubes.

    The new accordion amplifier also uses multiple output tubes and should be called "the series single-ended amplifier," but why start being sober after almost a hundred years of nomenclatorial whimsy. Besides, the accordion's expanding and contracting nicely symbolizes this amplifier operating principle.

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