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Old 3rd October 2008, 10:39 AM   #11
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I have a pair of Dynaco Mark III's with GSI front end boards that use 6dj8 tubes. It is the best MK III upgrade board I have ever heard. If anyone knows where I could find another pair of the GSI MK III boards for sale, I would be interested (populated or not).
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Old 3rd October 2008, 10:58 AM   #12
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I have a Tube God HV reg board i am trying to identify.

its an HV-1 from 89 i think. I have just finished drawing out the schematic of it. has Three TO-3 Pass devices on board. its for sale once i figure out what it is for.


Zc
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Old 3rd October 2008, 04:58 PM   #13
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Default Hey there

Should either of the last two posters need help (with HV regulator or GSI driver board), I can help.

Drop me a note: andy@fuchsaudiotechnology.com. I could make up a driver board or two fairly easily.

I could assist with the HV reg as well. it's a pretty simple series pass device using MJ-423's and I believe a TIP-50 and a zener string. Nothing fancy, but they worked well. If I were to make one today, I would likely use a Hexfet. I have used some devices that are 800-V 10 amp's and work well.
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Old 27th November 2008, 12:36 PM   #14
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I managed to get one off ebay. Naturally it didn't work correctly and I repaired it and got it running again. I think it has way too much feedback as the information I received says the feedback resistor should be 100K and it has 20K. One of the problems the amp had was a broken feedback connection in the left channel which resulted in a louder signal. It sounded massive with no feedback.

Picture of the amp.

I don't know if I will keep the driver board in there or switch to one of my boards that is a rework of the 6SJ7 input and 6Sl7 long tail design with CCS. I would be interested in hearing of others opinions on the GSI driver board. Also, would performance gains be had by using HV regulator boards to power the driver board?
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Old 27th November 2008, 12:40 PM   #15
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Quote:

its an HV-1 from 89 i think. I have just finished drawing out the schematic of it. has Three TO-3 Pass devices on board. its for sale once i figure out what it is for.

Drop me a line
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Old 28th November 2008, 03:05 PM   #16
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Default FB resistors

The values depend on the power tubes used and the resistor on the grid to which the feedback returns (it's a differential front end with audio and feedback inputs). We used it with 8417's triode connected, as well as EL-34's and 7591's, so the FB values changed based on the tubes used.

I usually aimed for about 15 db of gain reduction from the feedback loop, as I recall. Still trying to find an accurate schematic in my archives. Heck, it's only about 30 years old....
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Old 29th November 2008, 01:33 PM   #17
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I have been working on my ebay find with the GSI board trying to get the bugs out as its a classic example of killed by technician. I haven't seen soldering ability like it posesses since I let my 11 yr old grandson try to solder something.

I seem to be making progress slowly and its showing by its improved audio detail. I'm willing to keep working on it because its showing promise and I judged it harshly before I analyzed the errors that the prior owners made. I am told that it should be using photo flash capacitors but it has none. Is there a specific difference between them and standard caps?

Also the CCS circuit which I haven't examined yet contains 2) LM334Z which I have't seen or played with before. Is it one for each 6922? Would this design benefit from using DIYAUDIO current sources?

Could this design be modified to use other tubes? The 6FQ7 would really trip my fancy.
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Old 30th November 2008, 02:06 PM   #18
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Well, it went bonkers again. Now the voltages are off.

Right channel pin 1 128VDC, pin 2 85VDC, pin 3+6 85 VDC, pin 7 input, pin 8 2.46VDC.

Right channel pin 1 363VDC, pin 2 80VDC, pin 3+6 90VDC, pin 7 feedback, pin 8 2.41 VDC.

Help please
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Old 30th November 2008, 02:19 PM   #19
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Another picture and a thanks to an individual for sending me some information on this driver board.
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Old 30th November 2008, 02:58 PM   #20
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anybody?
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