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In Reply to: diy otl posted by Paul Barker on October 18, 2004 at 01:03:42:
I did 3 of my own design (unfortunately, 2 of them developed power supply problems perhaps because I wound my own 1400VA toroids & I suspect one may have developed an interwinding short (not a good thing in a transformer that size) & the other may have had its 'cool' turn on circuit crap out - haven't found time to fix those two yet but still running my original prototype for 16 years now - showing the amp topology itself is sound. My design is fully balanced & dc coupled (by this I mean you put dc at the input, you'll get a steady dc at the speaker terminals relative to the ground return). No servos, output stabilized by feedback, only solid state devices are in the power supplies (rectifiers & turn on circuit).
Follow Ups:
what tubes are u using and how often do u R&R them?
6bk7b's at the input, 6au6's & 6bl7's in driver circuit & 6as7g's at output. Many of the tubes are original from 1988, including perhaps half the outputs. Now's probably a good time to at least replace the remaining original output tubes. I'm going to rebuild the bias and offset adjustment circuits for easier accessibility, IAC, since the original potentiometers were sort of slapped in there and require disassembly to adjust (this amp was originally going to be just a prototype for a much higher powered pair of OTL monoblocks using 6lf6's, but I liked the prototype enough to stay with it, instead and eventually sold the sweep tubes to Richardson).
Is your circuit available for us to see? It sounds like a good design.
No, it's not posted anywhere, and I'm a little reluctant to do so without some sort of intellectual property protection (which I've never got around to getting) because the overall circuit topology is really substantially 'different' from anything else I've seen:)
I understand, I have the same feeling regarding my OTL amp:)
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