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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: Do all OTL circuits use double triodes as inputs and ouputs? posted by Frihed89 on January 21, 2007 at 03:25:12:
Classic Futterman OTLs used all pentodes, from input to output. If you are really "green" in this area then maybe you don't know that just about all commercially successful OTLs are PP types and have been or are based on only one of two topologies: (1) the "totem pole", so called because the anode of the "bottom" tube in a PP pair that is closest to ground (cathode to ground) is attached to the cathode of its mate, which in turn has its anode attached to the output power supply, OR (2) the circlotron, which is a fully balanced PP output stage that looks like a bridged pair of SE amplifiers. Julius Futterman patented the totem pole topology back in the early 50s or late 40s and had a company that made amplifiers. Transcendent amps are based on the Futterman circuit. Atma-sphere amps are based on the circlotron, but the idea of a circlotron also traces back at least to the late 40s (or so I have read). The recently deceased Tenor Audio company sold amps also based on the circlotron. And BAT amps are basically transformer-coupled circlotron types. It's possible to build the totem pole circuit with triode outputs (a la Fourier and maybe Graaf), but I don't know whether it would make sense to build a circlotron with pentodes. Basically in any OTL you want to use tubes with a very low plate resistance, not usually a pentode or tetrode. Futterman used gobs of NFB to get a low output Z.
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Follow Ups
- Absolutely not - Lew 20:57:49 01/21/07 (1)
- Re: Absolutely not* thanks LEW - tubevibb 21:05:03 01/21/07 (0)
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