Hi all,
Just got an ST-70 that needs quite a bit of TLC, and, as I've done with my MKIII monoblocks years ago (with great returns), I'm embarking on upgrading the stock design.
Now, a lot has happened since I last looked at Dynaco upgrade boards/kits. Some have gone away, others may have joined the club. I'm wondering if anyone has fresh thoughts on this - of maybe not so fresh but still valid and relevant. I'm currently leaning on Curcio's premium upgrade board.
I'd even consider designing my own board (PCB). Are there any interesting circuit designs out there? If I get really restless, maybe I'll pull a blank sheet of paper and try ground up. I'd probably try something like an LTP w/ CCS up front and I'm not sure about the phase splitter.
Either way, I'd probably prefer something like triodes through with DC coupling if possible. I have a very healthy stock of the 6DJ8 family (acquired through the years. for my AI M2C preamp).
Thanks all in advance for pitching in!
Just got an ST-70 that needs quite a bit of TLC, and, as I've done with my MKIII monoblocks years ago (with great returns), I'm embarking on upgrading the stock design.
Now, a lot has happened since I last looked at Dynaco upgrade boards/kits. Some have gone away, others may have joined the club. I'm wondering if anyone has fresh thoughts on this - of maybe not so fresh but still valid and relevant. I'm currently leaning on Curcio's premium upgrade board.
I'd even consider designing my own board (PCB). Are there any interesting circuit designs out there? If I get really restless, maybe I'll pull a blank sheet of paper and try ground up. I'd probably try something like an LTP w/ CCS up front and I'm not sure about the phase splitter.
Either way, I'd probably prefer something like triodes through with DC coupling if possible. I have a very healthy stock of the 6DJ8 family (acquired through the years. for my AI M2C preamp).
Thanks all in advance for pitching in!
A buddy upgraded his with a Dynaco Doctor board (three 6DJ8s). He was happy with it until a cat peeded on it and fried the whole works.
S.
S.
Oh, man... I'm not sure I can perform this upgrade, having not one, but two cats! 😉
I made a custom board for someone a while back and have a couple of them... It uses a pair of 6U10 Duodecar tubes.
Let me know if you're interested in more info.
Let me know if you're interested in more info.
There are quite a few improved ST70 upgrades.
I have the Gregg-the-Geek DynaMutt board and it is superb. http://www.classicvalve.ca/ Looks like you will need to directly contacy Gregg.
Here someone has a review of SynaMutt vrs VTA boards: https://audiokarma.org/forums/index.php?threads/dynamutt-vs-vta-st-70-boards-battle.307160/
And i know one of our members, kevinkr, had a board, and it sounds like he still has some.
And if you want to go balls to the wall, Allen Wright's PP-1c is VERY good (and can provide balanced input)
At the bottom:http://www.vacuumstate.com/index.dna?rubrik=8&lang=2&a=%9Ak%B1%E3%08%5Bw%90&b=738674.7406452827
The power trafo on the ST70 is another weak point. I am waiting for mine to die from being hot.
dave
I have the Gregg-the-Geek DynaMutt board and it is superb. http://www.classicvalve.ca/ Looks like you will need to directly contacy Gregg.
Here someone has a review of SynaMutt vrs VTA boards: https://audiokarma.org/forums/index.php?threads/dynamutt-vs-vta-st-70-boards-battle.307160/
And i know one of our members, kevinkr, had a board, and it sounds like he still has some.
And if you want to go balls to the wall, Allen Wright's PP-1c is VERY good (and can provide balanced input)
At the bottom:http://www.vacuumstate.com/index.dna?rubrik=8&lang=2&a=%9Ak%B1%E3%08%5Bw%90&b=738674.7406452827
The power trafo on the ST70 is another weak point. I am waiting for mine to die from being hot.
dave
Vacuum State RTP Preamp Problem
Do note that the driver board is essentially the RIAA section without the EQ.
It started with the PP1c and ended up as this commercial PP 300B amplifier. https://www.diyaudio.com/community/threads/any-comment-on-vacuum-state-dpa300b.98788/
Some here: https://www.diyaudio.com/community/threads/which-el34-kt88-pp-projects-should-i-consider.302078/
And here: https://www.diyaudio.com/community/...pl504-or-kt88-bal-innput.242962/#post-3642287
Brett’s pos is succinct: #30
Do note that the PS for the cascode front end really, really needs that rig in it. It is not the simplest.
I have been gathering parts for a dual mono version with EL84 (got all the ST-35 iron needed)
Do note that the driver board is essentially the RIAA section without the EQ.
It started with the PP1c and ended up as this commercial PP 300B amplifier. https://www.diyaudio.com/community/threads/any-comment-on-vacuum-state-dpa300b.98788/
Some here: https://www.diyaudio.com/community/threads/which-el34-kt88-pp-projects-should-i-consider.302078/
And here: https://www.diyaudio.com/community/...pl504-or-kt88-bal-innput.242962/#post-3642287
Brett’s pos is succinct: #30
Do note that the PS for the cascode front end really, really needs that rig in it. It is not the simplest.
I have been gathering parts for a dual mono version with EL84 (got all the ST-35 iron needed)
Thank you, very detailed response, and a good bit to weed through.
As I started thinking about this, one quick issue is the B+. I am planning to replace the GZ34 with SS rectification, and will likely end up with too much B+, given the stock ST-70 transformer.
I would really try to figure out hoe to put a biggish coke in the PS. It makes a difference and would help your vltage issue.
dave
dave
Good point. Need to figure DC resistance for it I'd want there. Also need to think this through regarding load though.
Check out the circuit for the "Super 70" in these Newsletters. https://avahifi.com/pages/audio-basics-newsletters There is a lot of useful info. I rebuilt my unit with this circuit "on the original board" as per the instructions, and it sounds wonderful. Like solid state but without any of the harshness, etc. It cleaned up the high frequencies amazingly, and the bass sounds good too. The Matching of capacitors, and matching of resistors, was a suggestion that works wonders for stereo imaging.
Don
Don
I'll second the DynaMutt board as being great, as I have one. It's a 6SL7 direct coupled to a 6SN7 long tailed pair with a CCS in the tail. Classic Valve also did a DynaMull with a 6EJ7 feeding a 6CG7 also with a CCs in the tail of the LTP. I don't know if Greg still has boards, and I wouldn't share the schematics without his approval.
I don't see anything on their website, so I have no idea what it is (though I appreciate your information). I can figure out more from corresponding website with just about any other products, so I'm not sure what I can do with that route.