I should have the schema but i couldn’t find it. If Gregg isn’t selling it anymore i am sure he will supply it.
He’s mostly doing musical instrument stuff.
dave
He’s mostly doing musical instrument stuff.
dave
Well, there's this: https://www.audiosciencereview.com/...vta-st-70-review-stereo-tube-amplifier.32353/. Not by the designer, but well documented measurements.
The original design reviewed here: https://www.audiosciencereview.com/...review-and-measurements-of-dynaco-st-70.7224/.
I've been working this morning on a PCB for Allen's PP-1 as featured on his website, and I'm having a really hard time fitting all parts on the ST-70 PCB opening. There are large resistors and electrolytic caps that take a lot of space.
I wonder if anyone else tried this.
I wonder if anyone else tried this.
I grew up listening to solid state gear. In 2007 I built a dynakitparts.com historical clone ST-70 kit (using 7199 tubes). It was the first piece of tube hifi equipment I ever heard. I must have completely bodged it the first time through, because after installing the VTA upgrade driver the amp sounded much better in every respect. Not saying the measurements are untrue, it’s just hard to believe the original driver circuit is lower distortion than the upgrade with CCS. I must have done something wrong.
That's one route... The other that came to mind is to have some parts underneath the board. I've done this pretty extensively with SMD boards design, though particularly for legged parts - not a big fan.
Just so no one is confused the KTA ST-70 mod Dave referenced in an earlier post has not been available since the early 2000s. The design was licensed later to a very well intentioned entrepreneur, but did not do well in the market due to considerable competition from better known outfits and designers. How many of you even knew that I designed audio equipment professionally for a living for >15 years? 🤣
That design is now over 30 years old, hopefully my old competition has innovated a bit over the ensuing years. The design was very loosely based on the Mullard 5-20 topology. I used a 12AX7 shared between both channels, and a single 6689/12AU7A/12BH7A as a long tailed pair to drive the outputs. It worked well. Today I would probably use a 6CG7/6FQ7 in place of the original 6689.
This is what the KTA ST-70 board looked like should you happen to run across one. I hand taped the PCB in the late 1980s using transfers etc from Bishop Graphics. I don't appear to have a modern schematic for this. (Now only on paper if I can locate it.) I think all told I sold about 30 assembled boards, and retrofitted somewhere around 5 amplifiers for customers.
I always found the ST-70 sounded better when wired for triode mode which depending on a number of factors was good for about 17Wrms per channel.
Found the schematic. Shared here for personal use.
That design is now over 30 years old, hopefully my old competition has innovated a bit over the ensuing years. The design was very loosely based on the Mullard 5-20 topology. I used a 12AX7 shared between both channels, and a single 6689/12AU7A/12BH7A as a long tailed pair to drive the outputs. It worked well. Today I would probably use a 6CG7/6FQ7 in place of the original 6689.
This is what the KTA ST-70 board looked like should you happen to run across one. I hand taped the PCB in the late 1980s using transfers etc from Bishop Graphics. I don't appear to have a modern schematic for this. (Now only on paper if I can locate it.) I think all told I sold about 30 assembled boards, and retrofitted somewhere around 5 amplifiers for customers.
I always found the ST-70 sounded better when wired for triode mode which depending on a number of factors was good for about 17Wrms per channel.
Found the schematic. Shared here for personal use.
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I put parts on both sides of the board I made, lets you put 10lbs of poop in a 5 lb sack so to speak:
http://getinthewoodchipper.com/?p=366
Sheldon
http://getinthewoodchipper.com/?p=366
Sheldon
A good friend was happy w/ this board- said it was easy to install and produced good sound. Didn't do any before/after measurements- he's not too technical, so it must have been easy, lol.
Jim
https://www.ebay.com/itm/372633540485
ps. reason for change was price of replacing 7199's. I recommended this PCB to him cuz my own listening of various tri/pent rolling showed 6gh8a to be the quietest
Jim
https://www.ebay.com/itm/372633540485
ps. reason for change was price of replacing 7199's. I recommended this PCB to him cuz my own listening of various tri/pent rolling showed 6gh8a to be the quietest
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That is most likely the closet one can get to high end replacement in st70. Everything else
seems to cost much more with no documented improvements.
And replaceing 7199 with tubes that is available is a good thing.
My head is currently at doing the Triode Electronics board (from affordable kits available) before this one. Price minus parts is about the same, and 51% of the fun is putting the kit together.
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[later:] This is from the TE website: "There's certainly other "dropin" boards, but most of them use 6GH8 or a similar triode/pentode which are a step back in performance compared to the original 7199, and no better than a 6AN8. Basically, you're getting improved quality parts, but no better performance otherwise than the original board if it had better parts to begin with...actually, on the average, 6GH8 have worse noise performance than 7199's do. Our board with either 6AU6/EF94 (ST70) or a cascoded 12AU7 (Mk3/Mk2 board), gives improved performance in this respect, and most people agree it sounds better, too."
I'm using the VTA 12AU7 board in mine with a 12BH7 for the ce ter gain tube.
Erhard Audio sells a board using 6SN7's with the power supply on the board also.
It's worth a look. VTA/Tubes4hifi sells a 6SN7 version also.
Erhard Audio sells a board using 6SN7's with the power supply on the board also.
It's worth a look. VTA/Tubes4hifi sells a 6SN7 version also.
Keven, you also had an interesting board for the Dynaco Mk. III.
The design in the MKIII was based on the PP 6550 amplifiers I was building at the time. It was basically a 2 stage differential driver circuit, it worked very well.