Mystery ST-70 Driver Board - diyAudio
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Old 10th October 2007, 09:33 PM   #1
Pyre is offline Pyre  Canada
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Default Mystery ST-70 Driver Board

Does anyone recognize this ST-70 driver board? It has 4 wima .47 uf caps and I believe it takes four 6DG8 tubes. It has no markings on it what so ever. I am sure I could figure out how to hook it up but a schematic would sure make it easier.

Thanks in advance

Shane
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Old 13th October 2007, 04:04 PM   #2
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It looks similar to the "Tube God" board sold by the late Harvey 'Gizmo' Rosenberg. I have one in my parts pile (the first mod kit I ever bought!), it's close but not exact. Mine used turrets for the off-board connections, and the layout is similar but not exact. Maybe yours is a later version?

The circuit used 6DJ8's in a cascode differential amp. Similar to Curcio's circuit, but without CCS loading. I doubt that I still have a schematic.

Bill
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Old 13th October 2007, 06:49 PM   #3
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Ye4s it it the first tube god stereo 70 input board - if you add a ccs it is actually better than the later cross coupled version
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Old 13th October 2007, 07:42 PM   #4
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Thanks!

I thought it was a Fuchs Audio board as he used to make a similar board a while back. I emailed Andy a picture on friday but have not heard back from him yet.

Has anyone a picture of Tube God Board?
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Old 14th October 2007, 03:51 AM   #5
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Quote:
Originally posted by Pyre
Has anyone a picture of Tube God Board?

From the depths of time, here's mine.
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Old 14th October 2007, 06:42 PM   #6
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So it turns out that it is indeed an Andy Fuchs board. I got an email back from Andy with a diagram and instructions on how to hook it up. Now thatís what I call customer service, supporting a product 20 years later that I bought for 10 bucks off eBay.

It sure does look very similar to the Tube God driver board. Maybe both were based on a similar concept that was popular at the time. I notice the Tube God board does not have any caps on the board. Were they taken off or not part of the circuit?
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Old 14th October 2007, 06:52 PM   #7
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Didn't Andy Fuchs work for Harvey in the early days of NYAL ? And the boards was designed by Brian Clark (I'm guessing)? It would may sense if they share the same "family" tree.
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Old 14th October 2007, 11:53 PM   #8
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Quinnling,
I know Andy, and yes, he did work with Harvey back when. And yes, I do believe Brian Clark designed the board/circuit. It's a dual cascode 6DJ8 differential with cross coupling at the upper grids. The tail resistor went to a negative source derived from the 5V recitfier winding which wasn't used being replaced with SS diodes. At least in the version I saw.

I saw Andy earlier this year and he's manufacturing some nice looking tube guitar amplifiers in a facility not too far from his old GSI digs.

Victor
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Old 15th October 2007, 12:27 AM   #9
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Quote:
Originally posted by Pyre
I notice the Tube God board does not have any caps on the board. Were they taken off or not part of the circuit?

The coupling caps (orange drops) were a bit large for the allowed space, so they're installed under the board.

Bill
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Old 7th November 2007, 03:09 PM   #10
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Default the "skinny"

The boards were made and sold originally by NYAL, and later were sold by my company GSI, after leaving NYAL.

The original boards were based on a design by John Syder, and we later changed the circuit to include cross-coupling and a discrete constant current sources. That design work was done by Brian Clark.

We also made another board with a 12AX7 and a 6FQ7 as cascade diff pairs as well. I'd offer the circuit here, but it's in a notebook I cannot currently locate. I've moved a bunch of times since then (over 25 years ago), so forgive me if I don't have the data readily on hand.

If there's any serious interest, I would be able to replicate the boards and sell them but it looks like this market has shrunken to a small one !
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