tomorrow i want a buy st70 !!! but i need many info:

knowledge base for the classic Dynaco ST70

Postby mati1979 » Tue Apr 14, 2009 9:21 am

SDS-PAGE wrote:.

hi SDS, i have read that you have pulished your chassis st-70.
This is a heavy work ? i want a pulish a chassis triode electronics. he comes in stainless steel (without sheen)
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Postby Slartibartfast » Tue Apr 14, 2009 11:06 am

burnedfingers wrote:Yes, those are 5693's and also my favorite. The driver board is a Mapletree and it uses 6Sj7/5693's and 6SL7/5691's. It is my favorite driver board for a Dynaco and I have used and or listened to them all.


Have you listened to an ST-70 with one of these driver boards? Class A operation.

http://www.kandkaudio.com/poweramplifier.html
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Postby SDS-PAGE » Tue Apr 14, 2009 11:39 am

hi SDS, i have read that you have pulished your chassis st-70.
This is a heavy work ? i want a pulish a chassis triode electronics. he comes in stainless steel (without sheen)


I don't know if it'd be possible for you to polish stainless to shine like chrome. I only tried their stainless chasssis for the ST-35 and it was definitely dull. I can't remember if it showed fingerprints on it. Nicely built though. Heavy too.

I used Blue Magic metal polish cream when I was cleaning up the ST-70 chassis. It worked great. It's cheaply available here in the US at local automotive parts stores like Kragen and Napa.
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Postby Quad » Tue Apr 14, 2009 10:22 pm

Also, check out Bob Latino's kit based on Roy Mottram's VTA board.
He sells on ebay too, if that suits you.

http://www.tubes4hifi.com/bob.htm
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Postby burnedfingers » Wed Apr 15, 2009 4:51 am

quote:
Have you listened to an ST-70 with one of these driver boards? Class A operation.

Yes I have. Not wanting to start a war here I will just say I wasn't impressed. SY on the diyaudio board has a superior driver board that he designed that uses 6SL7/5691's with Fets and transformers that sounds superior in my opinion.

Polishing a SS chassis.... the one in question has a grained finish. This finish will not come off easily and would be best left as is. It would take equipment that the average person doesn't own to accomplish the task not to mention the time. It would be very easy to take a Dynaco chassis to a small job shop and have them copy it using mirror finish stainless.
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Postby Vince » Wed Apr 15, 2009 10:45 am

Hi Burned.

You started this thread on DIYaudio:
http://www.diyaudio.com/forums/showthre ... genumber=1

Which you refer to above in this quote
"Yes I have. Not wanting to start a war here I will just say I wasn't impressed. SY on the diyaudio board has a superior driver board that he designed that uses 6SL7/5691's with Fets and transformers that sounds superior in my opinion. "

You were the recipient of some very good advice from some of the most talented people on that forum. The last post in the tread is dated 9-8-08.

You have yet to post on that thread the results of their advice.
I think you ought to do that as it is a significant modification of the ST-70 driver board.
Respectfully, Vince
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Postby burnedfingers » Wed Apr 15, 2009 3:44 pm

Image

Above is the circuit that I mentioned that SY came up with. It is simple, sounds good and delivers good performance.
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Comparison of the Triode and the Dynakitparts ST-70 chassis

Postby Bob01605 » Wed Apr 15, 2009 5:30 pm

Someone above asked about the differences between the Triode Electronics chassis and the Dynakitparts chassis for the ST-70. A comparison of the two chassis is below ...

1. Both are 18 guage stainless steel chassis and have the same 13 inch by 9 1/2 inch by 1 5/8 inch depth size. Your old ST-70 tube cage will fit either chassis. The Dynakitparts chassis, however, is electropolished and has a higher gloss mirror finish.

2. The Dynakitparts chassis has all the original Dynaco markings silk screened onto the front and rear face of the chassis. The Triode Electronics chassis has no silk screening whatsoever and looks kind of "bald" to me.

3. The Dynakitparts chassis has the layout of the punched holes identical to the original Dynaco chassis. The Triode chassis does not have the exact same layout as the original chassis and has one extra hole that they had to drill off center to near the center of the chassis to use as a bias measuring point. You wind up having to measure bias holding the probe over the hot driver tubes. With the Dynakitparts chassis you measure bias from the front of the amp from one pin on each power take off socket as you do on the original ST-70.

4. The Triode chassis has no quad cap cutout. You can't install a quad cap in their chassis. You are forced to use an underchassis quad cap replacement board which Triode just happens to sell also - hmmmm..

5. The Triode chassis is $137.50 and sometimes they have it on sale for $132.50. The Dynakitparts chassis is $125.

I guess you can imply by my statements above that I prefer the Dynakitparts chassis which I do.

Bob Latino
Bob Latino Custom Dynaco amplifiers

http://www.tubes4hifi.com/bob.htm
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Postby Slartibartfast » Wed Apr 15, 2009 7:46 pm

burnedfingers wrote:Image

Above is the circuit that I mentioned that SY came up with. It is simple, sounds good and delivers good performance.


No feedback is nice, but, does this bias the outputs into Class A operation?

Robert
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Postby battradio » Wed Apr 15, 2009 9:44 pm

Nice $70.00 transformer .There has to be a bias circuit to go with this and coupling caps ,resistors etc .



Mark
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Postby burnedfingers » Thu Apr 16, 2009 4:50 am

Quote:

Nice $70.00 transformer .There has to be a bias circuit to go with this and coupling caps ,resistors

I would gladly draw out something but I am afraid it wouldn't be very

readable and I don't have any cad programs anymore.

I used Altec transformers. Cost effective because I had them.

The circuit is just a simple one just to get the idea across. I think feedback could be introduced but I haven't tried it yet.

Bias circuit? For the output stage? Very simple to make. Coupling caps

and resistors need to be added and this goes without saying. I posted this

to show there are other options out there than can provide good

performance that don't cost an arm and a leg.

A power supply is needed for the Fets as you can see.

Quote:

No feedback is nice, but, does this bias the outputs into Class A operation?

Please correct me if I am mistaken but I always thought that biasing the

output stage in class A was a result of how you set up the amount of bias

in the output stage and the voltages run in order to get the correct curves.
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Postby Slartibartfast » Thu Apr 16, 2009 5:42 am

burnedfingers wrote:Quote:



Please correct me if I am mistaken but I always thought that biasing the

output stage in class A was a result of how you set up the amount of bias

in the output stage and the voltages run in order to get the correct curves.


That is correct, but, the K&K board also keeps the outputs in Class A, by the use of the two resistors as a Constant current source, or so I understand.
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Postby burnedfingers » Thu Apr 16, 2009 5:37 pm

If you like the K&K board then by all means purchase one. I hope it works out well for you ;)
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Postby Slartibartfast » Thu Apr 16, 2009 5:57 pm

burnedfingers wrote:If you like the K&K board then by all means purchase one. I hope it works out well for you ;)


It is on my wish list but, I am also just trying to find more options for the ST-70, that also provide Class A operation. [:)
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Postby mati1979 » Thu May 07, 2009 7:18 am

HI, I have semi assembly my st-70 :$ but i need help. (???)
in a pcboard i see 4 resistors different in compare with manual.
and i have free 4 resistors simil colour with a manual but not exactly colour. is correct fill with this 4 resistors in a slots R22-R23-R7 and R8 ?

Image

and in capacitor board i have empty a slots C11 and C12 (???) ,i dont have more components in my kit :(

Image[/img]
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