Project: eBay ST-70 with Rats nest inside.....

knowledge base for the classic Dynaco ST70

Postby DeathRex » Tue Dec 20, 2011 8:54 am

Don't understand why the mod uses a 6U8 and 5751 per channel. If you use the 6U8 to replace the 7199, a 5751 would give way too much gain. And there's not a whole lotta reason to use it as a cathode follower. (???)

Nevermind he says in his website.
At first I wanted to be a ET. Now I are one.
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It's alive!!

Postby Kyle Korum » Mon Dec 26, 2011 6:13 pm

So, I had the week off from work, and was able to button up this project. (cig) It sounds great! I didn't even need to chase down any gremlins at 1st startup, woohoo! I was both nervous, and excited at 1st startup -thought for sure that I'd have to track down noise/hum issues, 1 channel not working, or some crazy thing. It definetaly pays to double-check work as you go. ;)

Now, on with the pictures!

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The wiring of the older 2 board Welbourne Kit is a PITA! It was hard to keep things tidy inside. But, I think that I did a better job than the last owner!

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Last edited by Kyle Korum on Sun Jun 07, 2015 3:29 pm, edited 1 time in total.
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Postby DeathRex » Mon Dec 26, 2011 7:43 pm

Oh my that is purty. From that massive rats nest to a thing of beauty. I don't know who originally mangled it, but he should have his soldering iron and electrical tape taken away.

PS might want to clip the excess leads on that terminal strip next to the power transformer.

Very nice photography too.
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Postby Kyle Korum » Mon Dec 26, 2011 9:06 pm

DeathRex wrote:Oh my that is purty. From that massive rats nest to a thing of beauty. I don't know who originally mangled it, but he should have his soldering iron and electrical tape taken away.

PS might want to clip the excess leads on that terminal strip next to the power transformer.

Very nice photography too.


Thanks for the compliments! The leads that you are referring to, is actually 18ga copper, snaked trough the bottom of the strip -to tie up the ground. I had it though all 5 at 1st, then decided to isolate the middle 3 as the power supply ground, and make a separate point for the signal, which was placed at front of chassis. I could've removed the extra copper, but, I decided to keep it there, in case I wanted to try something else in the future.
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Postby Sal Brisindi » Wed Dec 28, 2011 10:36 am

Very nice job on the rebuilt. At least you no longer need a fire extinguisher from the condition it was when you purchased the amp.

Sal
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Postby dougm216 » Wed Dec 28, 2011 12:20 pm

Very nice work Kyle. Now enjoy the great sound.
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3+ years of use and still going strong!

Postby Kyle Korum » Sun Jun 07, 2015 3:57 pm

Hello all,

I updated some dead image links pertaining to this thread. Also, I've been giving this amp a lot of listening time since the rebuild, and I'm still in love with the high resolution and deep sound stage that you can really hear with a quality tube amp. I've done some experimenting with a few new production el34's, but even after burning them in; I always return to the old Tesla's that came with this amp. These tubes really shine at moderately high power levels, compared to the JJ's and Shuguang's I've tried. I'm REALLY kicking myself now for not picking up a few quads of the winged =C= EL34's while they were readily available.
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