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In Reply to: Re: feedback on b+of circlotron posted by Tubevibb on September 5, 2006 at 06:38:16:
Please give more details. How/where are you attaching the 1K resistor to provide NFB on the B+ rail? By the way, I am more than flattered that you would include me on a list with Mark (Gilmore) and Paul (Speltz); both of them are far more knowledgable than I am. Sadly, neither has patronized this forum for quite a long time, possibly because both are now more or less in the audio business. Adding a small resistor "on the cathode" (I presume you mean one resistor on each cathode of each output tube section) is not a new idea and indeed is a factory standard these days, though I don't remember what value Ralph currently favors. (Ralph posted on this a few months ago with their latest ideas.) It's always a good idea to be as explicit and detailed as possible, if you want a response.
Follow Ups:
IN THE BUSINESS.pass, cruil, even MR KARSTEN. O well wear here 0k I have a kit M60 an a diy MA1 14 tubes per amp, big transformers 4 1KVA at 140v+- loaded.I AWAYS CALL ATMA-SPHERE. SOME TIME BACK I GOT 5.5OHM 5 WATT.THE SO CALLED FEEDBACK 1K OR 500OHM U ARE RIGHT 1 5.5 OR 5 PER CATHODE.1K NOW ONE PER AMP AT THE CAPS.WELL THE CATHODE GETS FEEDBACK BY THE SPEKER SO THE B+NEEDS IT,MAKES BIG DIF. HELP ME IF U CAN. IF U DO NOT HAVE IT ON B+ LET ME NOW WHAT U THINK?
I think you are talking about the 1K ohm resistor that Ralph shows going across the two banks of caps that filter the LV supply (that is, the +/-140V supply for the output tubes). I built my amps from a schematic supplied by Ralph, and I therefore dutifully also installed that resistor, using a 5W or 12W Mills. There is no voltage across that R because both halves are at the same potential, so really a high-wattage resistor is/was not necessary. I never thought about it as a "feedback" element in the circuit. I think Ralph once told me that he was ambivalent about the necessity for it, but I left it in my highly modified MA240 amps.That said, I am not sure what you need "help" with. You seem to have done fine by yourself. If you want reassurance, OK, you got it. Your observation that the 1K ohm resistor makes an important sonic difference is very interesting; never experimented with it myself. I always assumed that the 1K resistor was used in all Atma factory-built products, but I would not know for a certainty.
Lew the 1K resistor does provide negative feedback and lowers the output impedance. At least that's what I found when I built my home brew circlotron OLT amps.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's been ages since I looked at the schematic, so could neither confirm nor deny that the 1K R provides NFB.
I HAVE PUT A CAP 6.5MF ON THE 800 OHM LIKE SILK,SAME AS ALL FEEDBACK I BY PASS.BUT I MUST SAY I CANT LIVE WITH IT.BUT THE CIRCLOTRON WE R FEEDINGBACK +/- OF SAME CHANEL.I ASK FOR HELP ON THE DEFF. BUT MAY NOT BE FAIR .I CAN MAKE CHANGES DAYLY. BUT THANKS FOR ALL INPUT I HAVE B&W 802M 804M 805N SNELL MAIII ACOUSTAT 3 ML LS3 ADS 810
...is easier to read, and the use of all-upper-case text looks as if you're shouting.
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Tin-eared audiofool and obsessed landscape fotografer.
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