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SCA-35 project and 7199's

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Posted on May 16, 2003 at 06:09:46
Donavon


 

Hey, a Dynaco forum! I just recently (finally) replaced the filter caps in my ST-70 ...also picked up four Philips 7199's at a guitar show, so I popped two of those in ...very happy with them BTW.

Anyway, I wanted to mention that I just got a SCA-35 recently that was working fine, but got the bug and decided to retube it ...put in the other two Philips 7199's and a quad of JJ's ...definately stronger now ...THEN after combing the 'net for ideas I started hacking away and eliminated all of the tone/balance/filter/loudness/stereo-mono garbage and that just really opened the this little gem up! Oh, I had to replace the volume pot too so I just put in a 100k RS Alps ...I'm so happy with this thing ...cutting out the tone controls makes such a huge difference ...I really didn't think it would be that dramatic. I will start shopping for cap replacements next but for now just taking time to enjoy.

 

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Re: SCA-35 project and 7199's, posted on May 16, 2003 at 11:42:44
JSTRM
Dealer

Posts: 414
Location: Montana
Joined: March 7, 2003
Contributor
  Since: August 28, 2008
 Donavon,
Can contact me direct about the SCA-35 mods?
Thanks,
jstrm

 

Re: SCA-35 project and 7199's, posted on May 19, 2003 at 21:16:47
Thomas Bombadil
Audiophile

Posts: 6
Location: Old Forest
Joined: December 14, 2002
 Anyone have a link to how to convert a SCA-35 to a power amp? I.e., a way to bypass the entire preamp section and drive it with a line-level input.

Tom B.

 

main in, posted on May 20, 2003 at 08:53:05
Donavon


 

There's two pair of wires under the power amp section that will get you right in ...just wire up a pair of jacks to those.

 

Re: SCA-35 project and 7199's, posted on May 25, 2003 at 20:05:29
Miles


 
To Donavon, ) I was interested in your statements about the SCA-35 that you had reworked and improved using information gathered from the net. I was particularly interested in the improvement by eliminating the front end controls, tone, loudness, stereo, etc which, except for the balance, I never use anyway. Could you share some details with me on how this was done? Is it simply a matter of disconnecting the 2 twisted pairs to the front end? I assume the JJ’s are the output tubes which in my case are 6BQ5’s. Any information you offer would be appreciated including any websites that were helpful to you. I built my SCA-35 in the 60’s and have enjoyed it all this while but a little perking up may now be in order. Thanks, Miles

 

Re: SCA-35 project and 7199's, posted on May 27, 2003 at 11:06:07
Donavon
Audiophile

Posts: 18
Location: Chicago
Joined: May 22, 2003
Ya, my wiring now goes directly from the selector switch to the volume pot and then to the power amp section which are those twisted wires under that board that holds the 7199's and the 6BQ5's.

The JJ's are EL84's which replaced the original Dynaco 6bq5's. It's a drop in replacement.

This page in particular was a big help to me but after trying to follow his steps it became apparent to me that the straight path I chose was the best:

http://home.netcarrier.com/~rstevens/sca-35.html

I still haven't started any cap replacements, but honestly it already sounds much better.

 

Re: SCA-35 project and 7199's, posted on May 28, 2003 at 12:45:38
Miles


 
Thanks for your quick response. I have a follow up question. Between the volume control and the loudness switch there are 2 capacitors and 2 resistors. Do I use these 4 components somehow or do I drop them out of the circuit? If I do not use these components there will be a red and green wire into the volume control and a red and green wire plus 2 black wires out of the control going to the circuit boards. Does that sound correct? Thanks Again, Miles

 

no loudness switch, posted on May 29, 2003 at 06:08:33
Donavon
Audiophile

Posts: 18
Location: Chicago
Joined: May 22, 2003
I took the loudness circuit out (so yes, disconnect those caps and resisters if that's what you want). I also replaced the volume pot with a 100K ALPS from Radio Shack (which I hope to upgrade sometime).

If I remember right (not looking at it right now) aren't there ALSO black ground wires from the switch to the volume pot ? Otherwise that sounds correct ...the center tap red and green going to the power amp circuit board.

 

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