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The BIG Dyna ST70 driver board thread

The Curcio premium board runs four of either 6DJ8/6922/6CG7.

I'm listening to one now with 4 (EH) 6CG7 (and 4 6B4G and and one 5R4 potato masher).
 
justinsweber said:
Very Similar... I think it runs 4 12AT7 tubes.... If I remember, the sockets were evenly spaced on the driver... Ill have to search through some pics to find.
Click to expand...

Okay. So I did a little research and here's my best guess: is it the Welborne Labs mod? If so, the Welborne Labs and the Kennedy Tube Audio drivers were two drivers I was aware of when I started this thread but neglected to mention for different reasons.

In the case of Kennedy Tube Audio the reason is simple. They're out of business, so their driver is not available except through second parties. Although, coincidental to my searching for the Welborne driver, I came across a website for the defunct Kennedy Tube Audio product line and at that site is page devoted to info about their ST70 driver mod. All the info for DIYers who want to roll their own is here.

As for Welborne Labs, leaving them off the list was a judgement call. See this thread here at audiokarma, this thread at diyaudio.com and this thread at audioasylum. So my reasons were threefold: I would have felt dishonest directing others to a company I would have felt uncomfortable doing business with; I thought it would be unfair to the linked businesses/forums with well-earned, honest reputations to be included on a list with a company with a poor reputation, and lastly, by all accounts they seemed to be going out of business so why mention them anyway?

Well, in all fairness, they're still around and I haven't seen any recent complaints so perhaps things have been worked out and, in the parlance of our time, it's all good. The link's above. Caveat emptor.

On a different note, since I've linked to the ST70 driver schemes of SY (from diyaudio.com) and Kennedy Tube Audio for the benefit of DIYers, I suppose it's appropriate to throw yet another ST70 driver topology in for posterity. After all, this is the "BIG Dyna ST70 driver board thread." So the attached .pdf file is still available on a separate thread here at audiokarma and is a hand-drawn schematic by Pakprotector. Anyhow, the topology is called e-linear because it takes feedback from the primary of the output transformer, yet not exactly in the manner of ultra-linear. Douglas (Pakprotector) developed the idea with Pete Millet, who gave it the name e-linear when he worked for/at Emotive Audio. Some of the technical details of the concept were also discussed way back when in the Radiotron Designer's Handbook 4th Ed., so there ya go.
 

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To give Douglas/Pakprotector a "we" bit more credit, it was one of his idea's/implementations while him and Pete
were working at the same time an Doug's been perfecting it a while now with Pete using it SE, an so the naming.
 
I think it was the Curio mod... So expensive...

I am using a Cap baord form Mr. Chong... nice setup... with a Weber Cap...
He (C. Chong has a 4 12AT7 driver for the ST70... but feels its not ready for release. I had seen someone else did something very similar... I guess it was the Fully monty from Curio.

The threat is incredibel in the detail.

You look at doing it for all the hobist ams St35 MKIII, Ecio and Heathkits alike.
 
Thanks Kegger. That's twice in a month that you've had to clean up after me. :twak:

Thanks for all the contribution.

BTW, have you tried/heard the e-linear scheme?
 
I have not tried it YET..:) (I have some projects where I am considering it though)

I have heard it quite a bit, and to be honest I wasn't quite that fond of it in the first
few amps I heard, but the last 3 Doug's done with it sound excellent, to me anyway.

I found it to be quite sterile an lifeless on the other amps, I can only assume Douglas
has reworked some properties of the circuit with the last few that I have heard now.

Others may have liked the early versions, as It reminded me of say a Citation II amp
in it being very "clinical" sounding and some really like that super clean performance.

Don't sweat the cleanup, people do it for me all the time, I need a lot of cleanup here..:)
 
Just a few more ST70 modification links of interest:

First link is full of info about the ST70 revamp service offered by Audio Research Corp. in their early days (mid 70s). It's the ARC ST-70-C3. This linked website is outstanding; there's lots of pictures of the amp, the power supply and the driver, .pdfs of typed correspondences, schematics, and user manuals, as well as suggested modifications to the original and a parts list! VERY strongly recommended viewing.

The other link is to the Audio Express page where you can order a reprint of their "Brute" issue. Brute being what they called their ST70 rebuild. I have the issue and flip through it often. Has parts lists and schematics.
 
Just wanted to add this link to a more recent ST-70 driver thread I read through here. Adds a little more perspective on the driver discussion.

I'd also like to add that I think the slagging of Roy Mottram for his Glass Audio review is a little tired. Perhaps it makes it easier on the pocket book to discount his driver design because of the shoot-out he conducted, but the failure to disclose his affiliation is not his responsibility alone. That is also what editors are for, and I don't hear anyone calling that to attention.
 
The editor of Glass Audio was not aware of Roy's affiliation until after the issue had gone to press. And Roy still presents the review on his website. The word "review" implies "un-biased".
 
I'm not really disagreeing with you about the lack of tact, I'm just tired of people bringing it up as if a simple editorial disclosure - an editorial disclosure that was not Roy's responsibility - wouldn't have cast the review in a less scandalous light.

But you're right about him being biased. And I think it's worth pointing out, biased does not mean the same thing as wrong.
 
Just found this thread as I was looking for a hi-tech member who might help me out with my amp. I did a Curcio Premium modification back in 2005 and I love it, in fact I loved it so much I sold my Granite Audio mono block amps after completing it. Now however something has gone awry! I'm experiencing background hiss (fairly loud) along with a faint but constant tic, tic, tic sound. I took the tube and bottom covers off and all I saw was a brown spot on the power supply board like something overheated but it didn't look catastrophic or anything. I guess if it would have been the amp wouldn't work at all, huh? Anyway, I'd appreciate any and all suggestions as to what to test and how and hopefully with a little direction I can get it up and singing again like it did before. Thanks! Nelson
 
Hey,
I'm also curious about the "Dynamutt" boards also...anyone build the octal or Noval version.. preference?
cheers,
Kirk
 
Thanks,
I have another ST-70 awaiting a rebuild, I have done the low gain VTA board for one but was looking for a reasonably price variation to try out on the other...the Octal might be the ticket.
 
:lurk:
A Stereo 70 driver board upgrade is high on my to-do list. I'm intrigued by the Dynamutt board (octal) and I'd like to read more listener impressions before I proceed. Especially interesting will be comparisons with the VTA board by people who have experience with both.
 
Me Too!...maybe someone can weigh in on the octal,noval, VTA comparison. Thoughts on the circuit design?
Cheers
 
I used to have a ST-70 with a Curcio premium driver board and an SDS cap board. I sold it several years ago but, wish every day that I hadn't. It had JAN 6922's and Svetlana EL-34's. The cap board had to be modified to work with the premium board. I had mostly Dale resistors and the coupling caps were Multicaps. The cap stages were jumpered into one bank of caps. That amp sounded sweet like a 35 WPC amp should and had balls to boot.
 
Brinkman said:
Okay. So I did a little research and here's my best guess: is it the Welborne Labs mod? If so, the Welborne Labs and the Kennedy Tube Audio drivers were two drivers I was aware of when I started this thread but neglected to mention for different reasons.

......

As for Welborne Labs, leaving them off the list was a judgement call. See this thread here at audiokarma, this thread at diyaudio.com and this thread at audioasylum. So my reasons were threefold: I would have felt dishonest directing others to a company I would have felt uncomfortable doing business with; I thought it would be unfair to the linked businesses/forums with well-earned, honest reputations to be included on a list with a company with a poor reputation, and lastly, by all accounts they seemed to be going out of business so why mention them anyway?

Well, in all fairness, they're still around and I haven't seen any recent complaints so perhaps things have been worked out and, in the parlance of our time, it's all good. The link's above. Caveat emptor.

.....
Click to expand...

Hi fellow AKers...

sorry i don't post as much here as i'd like too...
just too much junk going on i guess...

anyway, I too saw all the negative press for the last few years WRT Welborne... even experienced it myself when i tried to get down to their shop (in Denver) before they relocated to OK...

all that aside, i kept comming back to how much folks who have the welborne mod done to their ST-70s seem to really like it, from the reports I read... well, aside from the zenner diode issue that is reported by some...


well, a few weeks ago... I saw the Welborne/Kimmel mods were on sale for a very reasonable amount. (it's revision F of the mod)

I took the plunge, and less than three weeks later I seem to have all the parts for the "pimp my 70" kit -- the tubes/yellow caps/sockets were shipped a week later than the rest of the package, due to Welborne awaiting shipment...

as an aside, this amp is an early DIY Dynakit unit, as evidenced by the flathead screws, cloth covered transformer wires (and tranny numbers), and nickel plating...

will keep you all aprised of progress...

just wanted to let some folks know that sometimes things can turnaround...
 
Update: New Boards, related threads...

Some of you already know that there's new driver boards out right now, but I hadn't checked into it for a while so I thought I'd update this thread for the sake of posterity.

First off is a thread here at Audiokarma I wanted to link to. It is in regard to the low-gain version of the VTA ST70 driver (aka the Tubes4hifi board). Kegger here has tweaked the values a bit on it, "Keggerized" it if you will, and the thread is here.
(And here for updated values, http://www.audiokarma.org/forums/showpost.php?p=2426633&postcount=33)

Sheldon Stokes (SDS Labs) has redesigned his driver circuit, the former version of which was the prior iteration of the Triode Electronics boards before it was redesigned independently. Sheldon's circuit can be seen here.

Next up is an offering from a poster here, "Geek". He's got three PCB offerings (actually, four): a board with the original topology, a board that is an authorized reproduction of the KTA driver board (mentioned earlier in the thread), and his own clever driver design (in octal or noval versions). His design has a feedback loop and uses some CCS. You can order them here.

Here's links to three different threads on three different forums in regard to the Geek board (aka DynaMUTT) here, here and here. The last of which is a comparison between the Geek and VTA boards.

I'm feeling tempted to remove the K&K Audio driver and roll in some of these new offerings. Perhaps a new set of trannies and a chassis for the K&K driver so I can A/B...
 
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