Pics of the New Board

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Pics of the New Board

Postby Shannon Parks » Wed Mar 16, 2005 5:48 pm

They are here! I hope to wire one up tonight and start selling immediately. They look brown in the pictures, but they are actually a deep wine color. They certainly exude the retro look of the old brown PWBs or the original Dyna phenolic boards which will mesh nicely with the amp. But make no mistake, they are FR4 fiberglass and will last forever. Note the holes for tie wraps meant to secure AuriCaps. Yellow_Light_Colorz_PDT_02

Shannon


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Postby mesherm » Wed Mar 16, 2005 6:38 pm

Holy Sheep Dip Shannon, just go ahead and twist my arm and give me a reason to build another ST70... Yellow_Light_Colorz_PDT_09
Are they for sale yet?
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How do we order?

Postby gogzhad » Wed Mar 16, 2005 6:41 pm

I'll take three !
thanks,
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st70 driver....

Postby Shannon Parks » Wed Mar 16, 2005 9:43 pm

I can probably take some orders this weekend and ship them out Monday. I'll post test data, latest parts list, schematic & BOM this weekend. I basically left the layout alone from the prototype board, and just added the solder masks and silkscreens, so there shouldn't be any surprises. Yellow_Light_Colorz_PDT_10

Here's a zipped up, unedited 3.7meg picture pack of my stuffing session this evening. It's step by step.

Sample pic:
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Very nice!

Postby EWBrown » Thu Mar 17, 2005 6:44 am

You do great work!

What is kinda neat is to take all 28 pictures in the "pack" and then cycle them rapidly, like a slide show.

/ed
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Re: Very nice!

Postby Shannon Parks » Thu Mar 17, 2005 7:24 am

EWBrown wrote:You do great work!

What is kinda neat is to take all 28 pictures in the "pack" and then cycle them rapidly, like a slide show.

/ed


Hey, Ed! That's a very cool effect. It's like the old 'stick figure man walking with the pad of paper' trick. My cousin was particularly good doing those.

OK, I changed the file names to be more suited for this, ie 1.jpg became 01.jpg. I use IrfanViewexclusively. Great program.

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Postby TerrySmith » Sat Mar 19, 2005 9:01 am

Those are BEAUTIFUL! Are the 12AU7's in the same location as the orig 7199's?
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Postby Shannon Parks » Sat Mar 19, 2005 11:07 am

TerrySmith wrote:Are the 12AU7's in the same location as the orig 7199's?


Hi Terry,

By pure accident, yes, they are. I just checked. Why do you ask?

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Postby TerrySmith » Sat Mar 19, 2005 11:33 am

I have a Par-Metal chassis that I punched for a stock 7199 board with the tubes sticking out, for another DIY project using Heathkit AA-100 iron.

All I will need to do is punch a center hole with this new board.

But it's so pretty, I might go ahead and cut a big square hole!
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Re: Pics of the New Board

Postby Uncle Ned » Thu Mar 24, 2005 11:06 pm

separks wrote:They are here! I hope to wire one up tonight and start selling immediately. They look brown in the pictures, but they are actually a deep wine color. They certainly exude the retro look of the old brown PWBs or the original Dyna phenolic boards which will mesh nicely with the amp. But make no mistake, they are FR4 fiberglass and will last forever. Note the holes for tie wraps meant to secure AuriCaps. Yellow_Light_Colorz_PDT_02 Shannon[/img]


I take it you're roughly knocking off the HF87 circuit into the ST70?

Any reason that 12BH7 or ECC99 couldn't sub for 12AU7? There ought to be
enough filament current available on even an original ST70 power xfmr to support that.

Here's an idea: stick a filament jumper in there so 6CG7 or 6H30 could be used.
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Re: Pics of the New Board

Postby Shannon Parks » Fri Mar 25, 2005 7:18 am

Hi Ned,

Uncle Ned wrote:I take it you're roughly knocking off the HF87 circuit into the ST70?


Exactly. The LM334Z CCS is the key, as it permits usage in circuits that would otherwise need much higher B+ voltages to compensate for the voltage drop across the tail of the long tail pair phase splitter. Of course, then there's the well known benefits of a CCS tail for high phase splitter performance. But these benefits would mean nothing if the modified Mullard topology itself wasn't excellent - a perfect mix of performance and the classic 'tube sound'. Thermion has used half this circuit for the last year in a Mark III prototype PCB I made with amazing results.

Uncle Ned wrote:Any reason that 12BH7 or ECC99 couldn't sub for 12AU7? There ought to be enough filament current available on even an original ST70 power xfmr to support that. Here's an idea: stick a filament jumper in there so 6CG7 or 6H30 could be used.


Thanks for the confirmation on that, Ned. I decided against the jumper because I was afraid of stressing the power transformer any more. In my mind, I derated the PA-060 10% since some of the AC mains voltages in the US are way off these days, for example 128VAC in the town I work!

On my Mark III board I did have jumpers for switching the filaments for 6CG7s and indeed, Thermion and I have tested 12AU7s, 6CG7s and 12AV7s in this circuit. Thermion has told me he will cut-n-jumper his ST70 driver to run 6CG7s. FWIW, I've got the best test numbers using 12AU7s but kind of prefer the 12AV7s musically - maybe computer tubes are the best for processing digital music. Yellow_Light_Colorz_PDT_04 I just don't have a quality stash of 6CG7s. I'll have to test the 12BH7s.

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Circuit Variations

Postby Thermion » Fri Mar 25, 2005 10:22 am

separks wrote:Thermion has used half this circuit for the last year in a Mark III prototype PCB I made with amazing results.


Yes, I never thought the MKIII's could sound this good. It really made a remarkable difference from my upgraded stock circuit board. Some of the component values are different because we tweaked them for the MKIII's. We used somewhat higher plate resistors and ran a little more current through the 12AU7. Right now I am using some RCA 5751 and 5963 tubes. Very nice sounding, although the 12AV7's did have a very pleasing tone.

I have a similar modified Mullard circuit in my ST70 (Kevin Kennedy's circuit). I am going to replace that board with Shannon's using stock values at first, then experimenting with changes later. I am concerned about using 6CG7's in my ST70. It's a mid 70's version with the Japanese transformers. I will probably stick with 12AU7 family of tubes for the phase splitter, but want to experiment with others (12AT7, 6CG7, etc.) for the voltage gain.

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Postby TerrySmith » Tue Mar 29, 2005 5:29 am

Who sells those sockets? They look like good quality. It's seems hard to find decent sockets these days, I especially hate the ones with the small holes.
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Postby ashok » Tue Mar 29, 2005 5:48 am

TerrySmith wrote:Who sells those sockets? They look like good quality. It's seems hard to find decent sockets these days, I especially hate the ones with the small holes.


I bought sockets like those at http://www.partsconnexion.com/partscomponents.php.

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WIMAs or Orange Drops?

Postby EWBrown » Tue Mar 29, 2005 7:13 am

WHich caps sound better, WIMAs or Orange Drops? I've tried both in various sircuits and never noticed a real big difference. Reason I ask is that AES has WIMA "red box" MKP4 and MKP10 400 and 630V caps on "clearance" in addition to their APril thru June flyer specials.

I'm in process of putting together a Mouser order for the resistors, pots and caps, and LM334Zs. Just gettin' ready to upgrade a coupleof otherwise fairly stock ST70s... AES for tube sockets and WIMAs.

BTW I have some "pulled" original ST70 driver boards, yours looks positively beautiful as compared to the ones i have. Not as "toasted" as some ST35 and SCA35 boards I have seen. Old phenolic doesn't hold up well to the test of time.

/ed B in NH
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