ST-70 modifications

I have experience with both the Curcio mod and more recently with the Alan Kimmel kit that Ron Welborn sells. I've been extremely impressed with the Kimmel constant current design, but it really changes the character of the amp. If you like the romantic quality of the stock ST-70, I'd recommend the Triode kit. You'll get much better bass control & stability, and much better parts quality than the original Dyna parts.

The Kimmel design makes the ST-70 sound like a modern amp, much more extended highs and tight bass. It is still rich in the mid-range, but a lot less lush sounding than the original. Mine has Tung-Sol 6u8a's and black plate RCA's in the driver board, with Gold Lion KT-77's and Mullard rectifier. Frankly it sounds fantastic with appropriate efficient speakers. But it is NOT a kit for the unskilled, although I hear the latest version has better instructions. You need to be able to read schematics and should know something about tube amp construction. If I do another one, I would definitely do the Kimmel again, but I'm a masochist... YMMV.

One more kit you might look at, and that is the driver board offered by Mapletree Audio Designs. The MAD board is said to be very nice sounding, but I have not heard it myself, altho I have a MAD octal tube preamp I built which I like a lot.

there's a pretty good dyna board on AA you should check out. Lots of folks have trodden these paths. If you need help, just ask.

HTH

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.