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Old 1st October 2008, 02:01 AM   #1
dcb50 is offline dcb50  United States
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Default dynaco st 70 c3

hi, complete newbie here any body have a pic. of the component layout for the board on this kit?? I have one but is so faded cant clearly see much. this is the original board, any help at all .. thanks
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Old 1st October 2008, 02:20 AM   #2
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http://www.curcioaudio.com/st7_mnl.pdf

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Old 1st October 2008, 02:37 AM   #3
kmaier is offline kmaier  United States
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The ST-70-C3 was a modification by Audio Research Corp. Not a Dynaco at all actually, but an ARC design scaled into the Dyna chassis and using only the iron. Some details and pics can be found here:

http://www.arcdb.ws/ST70C3/ST70C3.html

I built a few of these way back... added DC balance to the output stage and a few other bits. Overall a very nice amplifier.

Regards, KM
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Old 1st October 2008, 03:52 AM   #4
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Awesome Schade strapping of the output tubes.
Triode emulation with full screen voltage! And
the OPT is wrapped into the local loop... There
are actually several more clever things going on
within this schematic.

Definitely one worthy of further study.
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Old 1st October 2008, 04:32 AM   #5
kmaier is offline kmaier  United States
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Actually, it was based on the ARC D-76 power amplifier but scaled back due to both physical space limitations and available power for filaments, etc. from the original components. Here's info for the D-76:

http://www.arcdb.ws/D76/D76.html

Regards, KM
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Old 1st October 2008, 05:11 AM   #6
dcb50 is offline dcb50  United States
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Default ST-70-C3 [DYNACO ST-70]

your absolutely right its not a dynaco!! but audio research calls it a st-70-c3 super modification kit for dynaco 70 .. that off the manual.. my question was if anyone had a clear picture of the layout of the component on the board?? THANKS..
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Old 22nd October 2008, 03:32 AM   #7
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Default ARC ST-70C3 kit

Hello
I built the amplifier on this page, or at least the amp showing in the botton view.
If you look closely, you will notice a regulator chip there for the first tube fillaments and a small bias trandformer next to the power transformer.
The original Dyna transformer ran the tubes at 450v B+
I changed the transformer for a lower voltage tranny, but 400ma versus 300ma for the original.
I had to add the bias transformer because the new transformer did not have a bias tap.
bob


http://www.arcdb.ws/ST70C3/ST70C3.html
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Old 22nd October 2008, 04:38 AM   #8
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Anyone know the impedance of the output trafo on the ARC_D76A and where I can get a PCB?





Thanks

Lawrence
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Old 8th December 2008, 09:42 PM   #9
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Default ARC ST-70-C3 PCB layout

The diagram you seek is on page 14 of the St-70-C3 Modification Manual, a PDF copy is in the link toward the bottom of my webpage dedicated to this amp:
http://mpbarneyamps.googlepages.com/...70-c3amplifier
Best regards,
Mike
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Old 8th December 2008, 09:58 PM   #10
SY is offline SY  United States
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Lawrence, 4k3, but 6k6 might work slightly better.
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