ST-70 modifications

I've done several of the Triode Electronics mods on a couple of ST-70s and also a set of Mk-IIIs. These were all full mods where not only was the cap board replaced but the driver board as well. I just finished a gut-rehab of a ST-70 which now powers my second system. The modded amp runs 6L6GC outputs instead of EL34s.

The Triode mods are well thought out and documented and they have a great deal of flexibility. You can use a variety of output & driver tubes (as in my example above) and you can even run the driver board, the outputs or both in triode mode.

In short, the Triode Electronics design is a first class option.

PS, the instructions for the Triode mods are available on their web site if you search a bit.

I've also worked on a Curcio modded amp. It was good but I prefer the Triode option.

K&K Audio has a mod package for the ST-70. It converts the amp to 10 watts triode. Might be worth looking into.

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

The K&K Audio mods for the ST-70,sound amazingly good. I had one in my system for a couple weeks.