ST-70 modifications

Just to add a little more detail to my request, I am not an experienced DIY'er. I have made interconnects and refoamed speakers but that is about it. I am pretty comfortable with my ability to solder and follow instructions and take my time on projects, but I have never built or rehabbed an amp or preamp. So along with the quality of sound, I need something relatively simple to install.....I would prefer a completed board as opposed to a blank board with all the parts and instructions. I think I need to replace the main driver board and the quad cap. Thanks again for your input.

Contact Oritek audio, Stuartbmw3. I just got back my modded ST 70 last week. Ori replaced the whole board, disabled the ultralinear mode, and made it a Triode(single-ended)with 18 watts. He uses no feedback. The live feel of the amp is fantastic! His price is the best also(You should hear his pre/dac, which beats many $3000 preamps.). It's all discrete components. In fact, I tried to put a review(sort of)of his Stereo 70 over the weekend on Audiogon. You can't go wrong with his amp. Please give him some time to work his magic, as he usually doesn't offer this work. As I remember the Stereo 70, this doesn't sound like it. It is very detailed(more than my Nuforce's), dimensional, fast-it just sounds more like music than what I am used to.

I had owned quite a few modded Dyna. One which I was fond with is the (defunct) GSI mod. It had 6DJ8/6922 in the driver board. I had modded an ST70 with the Triode driver and power supply cap boards. It sounds quite nice, balanced and detailed. I initially used Kimber coupling caps but have switched to Audiocap Theta bypassed with the Russian FT1 teflon, which is a few steps up. However, when compared with the Fisher SA-16 and Pilot SA-232 (both EL84 amps) modded with the same Theta/FT1, the EL84 amps easily trump the ST70 in my system, even with reissue Genalex KT77 or JJ KT77 in the Dyna. My ST70 does not have stock Dyna OPTs though, it has Magnequest/Kimber OPT. That said I can recommend the triode boards as they do have excellent documentations.

Quoc -- you gotta love those vintage EL84 amps! I have the Pilot SA-232 also and it is really sweet. The Eico HF-81 has had some good press lately. Mine has been in the family since my uncle built it in 1959, still sounds great!

But for the original poster, stay away from the Welborne kit if you are not skilled at reading a schematic. I hear the new ones have better instructions, but I'd be wary of it. I'm anxious to try the K&K mod sometime. I love Kevin's phono pre.

Another ST-70 board that has been well-reviewed, and is a simple drop-in installation is the one offered by Maple Tree Audio in Canada. It uses octal tubes, which are right in line with the lovely classic sound of the Dynaco. On the other hand, I would strongly recommend a power supply upgrade at the same time you do an input board. Check out the Dynaco forum on AA where you will see lots of help and advice.