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Old 1st December 2008, 03:29 PM   #1
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Default Dynaco MK IV Mystery

A while ago a friend wanted me to take a look at his Dynaco MK IV amp. The power transformer had burned up and he wanted to know if I could replace it. I was able to find a replacement PA-135 thru Triode Electronics. My friend had brought over the other MK IV and his Audible Illusions Modulus 2D preamp. Unfortunately the amp still does not work and the other amp is wired a little differently.
The big problem is that these amps were modded with 8417 and 6DJ8 tubes.
I have not been able to find any schematic or info on how they were wired. The driver board that includes the 6DJ8 tubes says mk 3 on the back and GSI 84 in the corner , but it does not match anything I have seen on the web. The boards include 2 LM 334 adj. current sources and a MUR 420 rectifier diode along with 2 pots.
The input uses a 3N259 bridge rectifier along with some very large caps(330v 750 uf).

Any suggestions would be appreciated.
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Old 1st December 2008, 03:58 PM   #2
llwhtt is offline llwhtt  United States
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Eric ,

Check out the Mystery ST70 board post down a few posts. Burnedfingers and I are trying to figure his out also.

Craig
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Old 1st December 2008, 06:01 PM   #3
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I will post some pictures this afternoon.
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Old 2nd December 2008, 02:02 AM   #4
llwhtt is offline llwhtt  United States
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It's the same circuit, the board is just a single channel for MKIII or IV. The schematic posted by Burnedfingers should help you figure things out.

Craig
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Old 2nd December 2008, 02:50 AM   #5
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Default Mystery Dynaco MKIV Pictures

Here are some pictures
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Old 2nd December 2008, 02:50 AM   #6
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Default more pix

more
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Old 2nd December 2008, 02:50 AM   #7
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Default 1 more picture

1 more
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Old 2nd December 2008, 04:26 PM   #8
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Looks homemade, and thats a shitty wiring job.
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Old 2nd December 2008, 05:56 PM   #9
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"*******" about sums it up. I don't like poking around in there without a schematic, and even then, if it's "hot", 1 hand in the pocket
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Old 2nd December 2008, 09:07 PM   #10
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see the thread at

http://www.diyaudio.com/forums/showt...83#post1345283

for a comment about a similar board from Andy Fuchs, the principal of GSI.

Andy can probably help you out.
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