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Page 3 |
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2003 |
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Copyright © 2003 John Broskie All Rights Reserved |
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The Family of Circlotron As for the circlotron circuit, it’s no secret that it perplexes many, if not most tube practitioners. How does the current flow from tube to tube? Why are there two power supplies? Why is it by necessity a class-A amplifier, or must it be? Is it a single-ended or a push-pull amplifier? In view of all these questions and all the mystery surrounding the topology, I can understand the controversy when I wrote that the much venerated modern circlotron amplifier was functionally identical to the “normal,” one-tube-on-top-of-the-other push-pull amplifier. (Next I’ll be saying that Allah and God are one and the same. Hmm... When a Christian living in the Middle East prays, does he say “God” or “Allah”? Answer: “Allah,” as that is the Arabic word for God.) Now, let me add fuel to the fire: the circlotron amplifier, not the old classic Wiggins design with output transformers and pentodes, but today’s simple version without transformers, in all actuality, after the advertising department’s copy has been stripped away, i.e. when examined naked, is no big deal at all. Neither holding magical powers nor breaking any laws of physics, it is as boring (or as interesting, but not more so) a circuit as any totem-pole topology. It is, in fact, the biggest distinction without a difference in tube audio, which is saying a lot, given the singular, atmospherically-vertiginous, class-A nonsense this topic engenders. This amplifier is just one variation in a family of push pull amplifiers. In this family there are no black sheep or stars, as all its members perform equally well. While the arrangement, the layout, the scheme, the pattern, i.e. the topology of the amplifier may confuse many of us, but it does not confuse the power supplies or the tubes or electrons. “Heresy! Heretic! Where’s the firewood, stake, torch, and angry crowd of audiophiles?” cry they who have a vested interest in keeping circlotron mysterious. Heresy? First of all, the circlotron amplifier in the original Hall/Wiggins design, the one that used output transformers and pentodes, was an engineering marvel well worthy of praise and interest. |
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What a beautiful design: two floating power supplies that power the entire amplifier, input and driver stages included; the cross coupling of the driver stage to the output stage; the constant output tube screen voltages, in spite of swinging cathodes. A masterpiece. The only amplifier that should bear the name “circlotron” is this one. On the other hand, the version sold today, the derivative version, the one that uses triodes or triode-connected pentodes and forgoes the output transformer, isn’t worth one tenth of the fuss it receives. Not that it is a bad amplifier design; it isn’t. It just isn’t in any way magical. Let me explain, albeit in a backwards way. The boring, no-big-deal, totem-pole, one-tube-on-top-of-the-other, push-pull amplifier holds five main components: two large power supply caps (we assume a bipolar power supply), two tubes, and a signal reference (six components, if you wish to count the loudspeaker). These five can be rearranged without changing the amplifier’s total harmonic distortion (THD), power output, slew rate, or bandwidth. Rearranged? I’ve said it before: imagine that electronic circuits are intricate necklaces that use wire to hold all the components together. These necklaces allow a good deal of play, as long as the rules of current conduction are followed, i.e. power supplies are not shorted out, plates are more positive than cathodes. |
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Fi-Sonik Parallel-Feed Single-Ended Output Transformers Nickel Core Amorphous Iron Cobalt Iron |