Dynaco MK IV Mystery

eric0108 · 1st December 2008, 02:29 PM

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.

llwhtt · 1st December 2008, 02:58 PM

Eric ,

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

Craig

eric0108 · 1st December 2008, 05:01 PM

I will post some pictures this afternoon.

llwhtt · 2nd December 2008, 01:02 AM

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

eric0108 · 2nd December 2008, 01:50 AM

Here are some pictures

eric0108 · 2nd December 2008, 01:50 AM

more

eric0108 · 2nd December 2008, 01:50 AM

1 more

Tekko · 2nd December 2008, 03:26 PM

Looks homemade, and thats a shitty wiring job.

eric0108 · 2nd December 2008, 04:56 PM

"*******" 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

ken.berg · 2nd December 2008, 08:07 PM

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.

1st December 2008, 02:29 PM	#1
eric0108 diyAudio Member Join Date: Dec 2008	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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1st December 2008, 02:58 PM	#2
llwhtt diyAudio Member Join Date: Jun 2008	Eric , Check out the Mystery ST70 board post down a few posts. Burnedfingers and I are trying to figure his out also. Craig

1st December 2008, 05:01 PM	#3
eric0108 diyAudio Member Join Date: Dec 2008	I will post some pictures this afternoon.

2nd December 2008, 01:02 AM	#4
llwhtt diyAudio Member Join Date: Jun 2008	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

2nd December 2008, 03:26 PM	#8
Tekko diyAudio Member Join Date: Jan 2005	Looks homemade, and thats a shitty wiring job.

2nd December 2008, 04:56 PM	#9
eric0108 diyAudio Member Join Date: Dec 2008	"*******" 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

2nd December 2008, 08:07 PM	#10
ken.berg diyAudio Member Join Date: Nov 2003 Location: Tempe, AZ	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.