Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

Tube4Hifi ST70 mod Experiences

Posted by Lee of Omaha (D) on January 23, 2016 at 09:02:57

We recently modded our fifth Dynaco ST-70. It's a customer unit, so we were paid to install a factory-built board, do our mod to the power supply, unscrew some stuff someone else had done, supply the 6SN7s, bias and test.

This board had two upgrades: the Russian paper-in-oil coupling caps, and increased capacitance on the input board. It also has the later, larger power transformer.

It doesn't have our 500uF second filter cap, but 150uF in capacitance for the second cap. Still has 50uF of input capacitance.

It has customer-supplied JJ output tubes.

This is clearly the best-sounding ST-70 we've done. It sounds...neutral. Most importantly to me, it sounds not like a tubed amp, not like a solid state amp, just...right. Excellent dynamics, excellent separation of instruments.

So what's the difference between this amp and the others we've done? We're going to try to find out. The first avenue of inquiry is the russian K40y capacitors. We're going to change the caps in another ST-70 we have to K40Ys and see how it sounds.

I believe we're going to stop putting 500uF caps in the second stage and stick with 150 - 200uF there. It should be easier on the power transformer (slightly greater conduction angle) and since the bass on the current amp is so good (and un tube-like) I doubt that there will be any degradation in bass.

Previously I was really proud of our (and tubes4hifi's) mod, but thought the McIntosh 240 was still a better-sounding amp. Now I'd put the ST-70 up against it. It will take some investigation to discover which of the differences take it from really good to truly great.

But I will tell you that the lowly ST-70 can be a truly great amp. And this isn't commercial, so please mods, don't delete. We use the 6SN7 tubes4hifi board (no affiliation other than customer), and we beef up the power supply. There's our whole recipe, open source.

This post is made possible by the generous support of people like you and our sponsors:

Signature Sound

[ Signature Sound Lounge ]

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---