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작성일 : 04-09-14 09:52
[파라피드300B/SE] 모찌님,,, 트리뷰트 피터에게 ultrapath 개조에 대해 답신을 받았는데
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글쓴이 :
새잡이
조회 : 1,576
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이게 도대체 어떻게 하라는 건지 잘 이해가 안되네요.
선오디오 회로에는 각 300비 캐소드에 1킬로옴 저항이 각각 달려있읍니다.
그런데 이 사람은 그것 병렬로 묶어 공통 캐소드 저항으로 사용하라고 하네요. 그것까지는 알겠는데 그러면 각 캐소드 저항이 결국은 1킬로에서 500옴으로 변하는 것 아닌가요? 그럼 캐소드 바이어스 전압이 절반으로 떨어질 것 같은데.. 답신은 같다는 식으로 말하는 것 같은데... 어떻게 하라는 건지 도통 감이 안잡혀서 의견을 구합니다.
주고받은 원문 메일입니다.
now i am trying to tweak on sun audio sv-300b pp amp.
i already replced the electrolytics of B+ supply, and what i am trying is to remove the cathode bypass cap of 300b.
it is RC coupled to the ground as usual ( 1kohm+100uf )
what i am thinking is ultrapath configuration.
at first i considered fixed bias, but it is somewhat more complicated so i changed my mind to try ultrapath configuration,
yes, remove cathode cap(100uf) then connect from center tap of OPT and top of cathode resister. large value pp cap will be necessary here, so i also try mundorf mcap audiophiler here , cap value will be 47uf 400v each.
how about my idea ? would you advise me more on this ?
best
kim
Hi Kim,
Look at Lynn Olsen's Aurora schematic;
you could do the same with the Sun Audio amp:
Make one common cathode resistor for
both 300B's by parallelling the two 1k cathode resistors.
Try the 47uF capacitor like Olsen does
(he uses 31 uF); I think this is the best option (ultrapath).
Summer is coming to its end here too;
it is getting more rainy and colder.
Best regards,
Pieter,
TRIBUTE
thank you for reply.
sun amp 300b has 1k ohm+100uf cathode rc for each 300b tube.
you told that pararelling two 1kohms and make one common cathode resister.
but then, the cathode resister will be 500ohm...
then, it is not the same bias before, so i think pararelling two 2kohm will be 1kohm common resister.
am i right?
i saw the aurora circuit.
He used around 500ohm cathode resister and 31uf ul cap.
according to your equation the low pass will be 10.27hz(1/(2*3.14*500*0.000031) )
if i use 1 kohm cathode resister and 20uf cap for the ultrapath.
the low pass will be 8 hz.
am i right?
how about using 20 uf instead of 47uf?
the cap vlotage should be around 600 vdc, so 47uf is not available.
at first i thought 400vdc will be fine, but ultrapath cap voltage should be more than
B+voltage+300b ac swing voltage + 20%more. so around 600 voltage cap should be used.
let me have your final comments.
thank you
Kim,
indeed be aware of the needed high
voltage capability of the ultrapath capacitor.
The 500 ohm is right; bias is the same
because the bias current of BOTH 300B's run through the 500 ohm
resistor.
Regards,
Pieter
TRIBUTE
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