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Old 26th May 2006, 07:04 PM   #1
chrisvw is offline chrisvw  South Africa
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Default Best Use For My Sansui Iron?

Hi Everyone,

I was lucky to get two Sansui OPT's and a PSU trafo from a friend. They were sitting on a shelf in his garage, collecting dust.

Anyway, the OPT's are the same ones that were used in the Sansui AU-111. (410-5235) Originally, they were used with 6L6GC's in PP. They don't have UL taps, but have a 10% Cathode Feedback winding. Primaries are 4K, secondaries 16 and 8 Ohm. Power rating is 50 Watt.

The PSU trafo is not from an AU-111. Secondaries are: 0-330V, 0-330V, 0-87V, 13-0-13V, 0-6.3V. VA rating is unknown.

I have been contemplating triode strapping EL34's. But my speakers are 88dB sensitive, so I probably need more power. Alternatively, I could just build an AU-111 clone. (power amp only). But this calls for 485 Volt on the plates. I could get a Sansui PSU trafo copy made, but would like to use my 330V iron. Can the current production 6L6GC's handle 485V well? Could I perhaps use the CFB with EL34's in pentode mode?

As a relative newbie, my mind is spinning. I would love to hear your recommendations. I've posted this question at AA, and got interesting replies. But I still feel unsure...

Thanks in advance,
Chris
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Old 26th May 2006, 07:06 PM   #2
chrisvw is offline chrisvw  South Africa
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Default AU-111 Schematic

Here's the Sansui AU-111 PA schematic. Not sure if it's worth cloning.
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Old 26th May 2006, 08:07 PM   #3
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I personally don't feel comfortable putting 485v into a 6l6gc (I figured out the dangers the hard way). Officaly, an El34 can handle 485v but that still seems a little high
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Old 26th May 2006, 08:15 PM   #4
poobah is offline poobah  United States
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would KT88's or 6550's fill the bill? They will get get you the power want...

Use a choke in the PSU and bring it down to 400-420

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Old 26th May 2006, 08:32 PM   #5
kevinkr is offline kevinkr  United States
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The AU-111 is a good design, and 485V at reasonable currents is not totally ill advised for the 6L6GC, I would certainly recommend subbing the 7581 which IMHO is better sounding and a little more rugged as well.

Not a bad circuit to clone at all IMHO.
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Old 26th May 2006, 09:13 PM   #6
chrisvw is offline chrisvw  South Africa
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Default KT88

Thanks for the advice everyone.

I am quite attracted to KT88's. Poobah, do you mean KT88's in triode mode? I can source KT88EH tubes locally, but am wondering if JJ's would not be a better bet.

What driver/phase-splitter circuit do you recommend? "The Ultimate PP KT88 Amp" driver looks nice, but calls for 480V. I have a few nice 6SN7's for this application.
http://www.plitron.com/pages/Products/Audio/vtvkt88.htm

Anyone have experience with the 6L6EH? Would it handle the 485V in an AU-111 clone?

My dilemma: Building an AU-111 clone calls for a new PSU trafo. Using my 0-330V iron would free up money for more costly KT88's.

Chris
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Old 26th May 2006, 09:32 PM   #7
poobah is offline poobah  United States
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How much power are you after? I don't think that triode mode will get you there...
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Old 26th May 2006, 09:38 PM   #8
chrisvw is offline chrisvw  South Africa
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Default 35W would be nice.

35W+ would be very nice indeed. Triode will give me half that, but is easier to build. Were you thinking of using the KT88's in the AU-111 circuit with 485V B+?
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Old 26th May 2006, 09:48 PM   #9
poobah is offline poobah  United States
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35 Watts means NO triode mode.

I had no plan... Just 4K primary fits well with 6550/KT88... I know that 6550s will give you 35 Watts with your PSU tranny.

SY is one of the guys to want to ping here... I am a tube nube myself. I am pretty sure that SY has not fallen into the SE abyss.

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Old 27th May 2006, 07:35 PM   #10
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Hi Chris,

The sight of the Sansui iron made me drool

I have an AU-111 which I want to revamp but I am struggling to find a clear schematic of the whole receiver. Do you have the complete schematic scanned? I would really appreciate a copy of this if you do have it on your computer.
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