Restoring a ST-70

knowledge base for the classic Dynaco ST70

Postby Dynaco_WJW » Sun Jul 24, 2011 12:15 pm

@rmyauck -- Thanks for the posting. I did find posts of Joe Rosen, but haven't found his article yet. I lowered the bias voltage to 1,5V and I will listen if I can hear differences. I will try to find out graphically in the load line and working point, Who has experience with this for the EL84 and the ST-70 voltage?

@soundmasterg --$10 ..... Can you deliver me 10 of these? ;)
I also have some Multitone Maygra amplifiers who are on the attick for years now, so don't feel ashamed that you haven't finished your ST-70. It is not a lot of work restoring this amp, but start with it when you are ready and having fun to do it. In what shape is the chassis? I bought a board from dynakitparts. I chose this board because of the vintage look. One thing is sound, but the other thing is authenticity what I like. So I try to get a match between these. For my ST-70 I even used the old wiring. I did this because it is the wire used so many years ago. It was hard to get the right wire. Most of the diameter was different than original. If you have some pictures of your ST-70, don't hesitate to upload them. ;)

Here is a photo of the wiring.
Image
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Postby soundmasterg » Mon Jul 25, 2011 7:00 am

Dynaco_WJW wrote:@soundmasterg --$10 ..... Can you deliver me 10 of these? ;)
I also have some Multitone Maygra amplifiers who are on the attick for years now, so don't feel ashamed that you haven't finished your ST-70. It is not a lot of work restoring this amp, but start with it when you are ready and having fun to do it. In what shape is the chassis? I bought a board from dynakitparts. I chose this board because of the vintage look. One thing is sound, but the other thing is authenticity what I like. So I try to get a match between these. For my ST-70 I even used the old wiring. I did this because it is the wire used so many years ago. It was hard to get the right wire. Most of the diameter was different than original. If you have some pictures of your ST-70, don't hesitate to upload them. ;)



Yah I know, $10 is a fantastic price, especially with the great tubes in the bargain....haha. For me, I'm a full time college student for electrical engineering, and I have my own guitar amps, bass amps, RCA console tube stereo, guitars and basses to maintain, AND I fix amps for local musicians for extra money from time to time....have two on my bench right now. So while I would love to get the ST70 working, I have other stuff to do at the moment. I have a Scott 299B that my grandpa had to get working too. Anyway, my chassis is a bit rusty and I bought a new chassis from Triode just in case. I plan to get pics of my ST70 together once I start work on it. I may get it working as is and get parts to build another, and do a different circuit design on the second one to compare with this one. We'll see...haha.

Your chassis pics look really nice!

Greg
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