Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Dynaco-Doctor Forum ]

---

[ Alert Moderator ]

---

If I ever run out of projects

Posted by 1973shovel (A) on March 6, 2018 at 05:59:28

In Reply to: RE: "it is not a Dynaco any more" posted by xaudiomanx on March 5, 2018 at 16:59:39:

...I'll give running one channel of the two stock ST-70s amps a try. Given that the quad-caps in both are original, and both have selenium rectifiers in the bias circuit, it wouldn't be as easy as just hooking them up for an interesting afternoon experiment though.

I've got two MK-III amps which have been waiting for my attention for far too long. And another project which really interests me, which is building a 6BQ5 amp using a pair of Z-565 transformers I have, but on a custom ST-70 sized chassis, as shown below. (not my amp)

Given the excellent results I had with Dave Gillespie's EFB in my SCA-35, I'd use the same bias scheme for this amp, only I'd change it to individual EFB for each output tube. The added chassis space would allow me to use a choke, and maybe some room for those Wima DC Link caps in the power supply.

The real question is, what input circuit to use? Given the scarcity and price of NOS 7247, I wouldn't go with a ST-35 circuit. I bought a pair of current production JJ 12DW7/7247 and sent them to a guy who has a Fisher SA-100 which uses that driver tube. His take on them was that they were "just OK" (shrunken soundstage and "thin" if I remember correctly) compared to his NOS tubes, so that ended the idea of using the ST-35 input circuit.

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

Sonic Craft

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

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

---