Well this was simple enough to slam together. This upgrade from Ned at Triode is a popular one for the ST 70. I know, I know, I have to cheat and can't build from scratch like some of you but... It's all I can find time to do. Hope I got it all landed right and properly installed in the amp. Let cha know how it sounds soon...

WW,

That looks great! Glad I'm not the only one around here that knows how to modulate a slobering iron! ;)

Let us know how it sounds. What are those two outer tubes that don't look like dual triodes? They must be sharp cutoff pentode input voltage amplifiers. I'm guessing they must be sharing the middle tube (12AU7?) as the phase splitter for both channels?

I'm not familiar with this Dynaco, never had one. :( My loss I'm sure.

Rob

Say Rob...

The two outer tubes are Svetlana EF86's and yes you guessed right, they share the middle tube a Mullard 12AU7.

The Dynaco is a popular push pull 35 watt per channel tube amp. The older ones (like mine) had some nice hand wound output transformers. Seems the Dynaco's have a big following of aftermarket suppliers that offer various forms of upgrades etc. This old amp in it's stock form is likely nothing to write home about. I mean, it works but...When modified though it can turn into quite a good performer.

Tomorrow I throw it on the variac and bring it up slow. I double checked all my work and I feel it is dead on.

Neet, Sweet, Petite!
WW after you get that baby fired up remember that those EF-86s are really high gain and might need some shields.
Great looking job! Can you say Orange Drop? Of course you can!:D

Thatch...Thanks for the shield tip. I didn't realize that and likely have some shields around here. Ned at Triode didn't mention anything about it though and this mod has been sold often by him. I may dash off an e mail to see what others are doing in this case. Was gonna opt for even better caps than the orange drops but didn't want to get that involved at this point. Easy enough to do later and if I do any experimenting with this it is likely I will try hooking things up in triode mode and fool with that etc.

All installed and no smoke! :ntwrthy: Whew...But I was REAL careful stuffing the board then installing it in the amp. I must have triple checked my every move. Bias volts hit right on so I put the analog source to it and sat back holding my breath.

Sure am glad I got this mod finally done. Much cleaner sound and centered sound stage. It was nice to hear. I now have turned this old vintage Dynaco PP into a top performer that will stand with (chit above! Gotta luv them out put trans) any new PP amps in it's class. Plus now I can attempt triode mode as well as a number of different driver tubes and such. Fun, fun, fun!
:yippy:

Hi WildWest

I've done a couple of ST-70 mod/resto's in the past. One based on the Triode baord, the other on the Welborne/Kimmel mod. I found that the Russian EF-86s are harsh, and sharp enough to cut glass. NOS tubes will GREATLY improve the sonics of the board. The best tubes I've found so far are GEC Z-709s, and a black plate Sylvania 12BH7. I can't stress how much this helped. Also changing out the orange drop caps for something better will help as well. My personal faves for this are Auricaps. You might consider changing out the metal film resistors on the board with Rikens. Although I have not done this on the Triode board, I have done this on other projects, with excellent results. The Rikens are very detailed, yet warm. The aren't noisy, and don't drift like common carbon comps. I'm like you, and have not scratch built yet, but have gotten way into modding. Just now comming up with my own designs, cobalt core parafeed linestage from hell, and an interstage coupled 300B amp.

Enjoy,
twystd

Howdy Twystd;

You know...Initially I was going to order that board with no parts. Knew I could do better on the caps and resistors. Orange drops never really impressed me but, they work. Alas I was into a "get it installed now" mode and the whole bag of parts dropping in my lap just made it easy. I fully expect when things slow down for me and I have time, I will be changing parts out on this board.

Thanks for the tip on the tubes though. I'm running a black plate Slylvania 12 BH7A (had a Mullard 12AU7 in there) with the kit supplied EF86s I will give the 709s a whirl per your suggestion.

BTW, I forgot to mention you may have to change the value of some resistors on the board, in order to bias the EF-86s properly (I did). The proceedure is in the Triode instructions. It's trial and error, but the results are worth the hassel. Glad you found out about the black plate 12BH7.

twystd