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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Yes posted by Mark Kelly on April 14, 2004 at 02:55:09:
Well, let's see, to really approximate the fabled WE Harmonic Balancer you need a smallish cap going from the CT of the input trans to the paired cathodes, and a several-times-bigger cap going from the paired cathodes to the CT of the OPT (or interstage).This lets you set the ratios of the desired common-mode modulations, or distortion-cancellation if you are clever - and I bet the WE guys worked out the math pretty exactly - this was the early days of feedback, after all, and the theater amps had the best engineering of the day. What's not so clear if all this sophistication was merely to reduce hum, or the more exalted goal of lower 3rd-harmonic distortion.
Another really subtle refinement would be separate bypass caps for each side of the filament circuit, thus removing the small inductive/resistive loss of the filament trans CT connection. You'd have to match the caps pretty exactly, though, otherwise you'd get hum from AC heating filament circuit. Then again a small trimmer cap could be switched into one side or the other to minimize hum.
Yes, Mark, you've stumbled onto something really quite deep and remarkable - a very interesting form of common-mode feedback that only acts on trans-coupled balanced circuits. Fun fun fun (to the closing tune of Red Dwarf).
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Follow Ups
- Variables to play with ... - Lynn Olson 04:31:24 04/14/04 (3)
- I want to be shipwrecked and comatose... - Mark Kelly 05:32:39 04/14/04 (2)
- I hope you (and all the rest of us) succeed - Lynn Olson 01:56:55 04/15/04 (1)
- Your loop discussion was what rekindled my interest. - Mark Kelly 04:02:42 04/15/04 (0)
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