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The Dynaco SCA-35 is back!

64.223.229.214
Posted on April 13, 2014 at 11:35:38
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi, Did you guys notice that the Dyna SCA-35 is back. It looks like 1000 bucks. I wonder how good the volume controls are and why the scratch filter and loudness circuits were still included for the purists of today.....Mark K.

 

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RE: The Dynaco SCA-35 is back!, posted on April 13, 2014 at 12:23:00
fstein
Audiophile

Posts: 2994
Location: fstein
Joined: May 18, 2006
 all dressed and built, $1300

 

Nice to see they're using Dave Gillespie's EFB mod for biasing, posted on April 13, 2014 at 13:24:43
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 That simple modification makes quite a difference in the sound of an SCA-35 or ST-35.

I had to do a bit of searching to see that they're using 6GH8 as the input tubes on the amp board, since the ebay ad doesn't say. That's a good thing, because as Eli says, the 7199 is "unobtainium"

 

RE: Nice to see they're using Dave Gillespie's EFB mod for biasing, posted on April 13, 2014 at 14:56:55
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Shovel, on the post I mentioned the volume controls. I'm sorry I meant the tone controls. With such a project wouldn't you think they would leave those out and style the faceplate accordingly? Loudness and filter too. Also, why would the SCA-35 have the 2 hum pots on the back if they got rid of the noisy 7199 tubes in the Gillespie mod. My ST-35 amp (stock) does not use the 7199 and has no hum pots. Just a thought Shovel...Mark K.

 

RE: Nice to see they're using Dave Gillespie's EFB mod for biasing, posted on April 13, 2014 at 15:36:49
Steve O
Audiophile

Posts: 12364
Location: SE MI
Joined: September 6, 2001
 The hum balance pots in the SCA 35 are for the low level preamp stages and re not related to the power amp driver tube. The ST35 is a power amp and has no need for hum balance pots...if nec they'd be in the outboard preamp.

 

RE: Nice to see they're using Dave Gillespie's EFB mod for biasing, posted on April 13, 2014 at 15:39:22
Flyquail56
Audiophile

Posts: 582
Joined: February 5, 2002
 Hum pots are on the SCA-35 for the phono stage, due to the AC on the filaments. This is why there are no hum pots on the ST-35.

 

RE: Nice to see they're using Dave Gillespie's EFB mod for biasing, posted on April 13, 2014 at 21:21:15
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi SteveO and Flyquail56, thanks for the great answers. I had no clue and learned a good lesson. Thank you so much...Mark K.

 

RE: The Dynaco SCA-35 is back!, posted on April 14, 2014 at 06:24:15
Brian Levy
Audiophile

Posts: 2438
Location: Toronto
Joined: June 5, 2000
 Happy to see someone is making the unit again, one of my favorites. I too question the tone controls and use of PECs.

Also, I would have preferred a larger chassis as the original is too small for the amount of heat generated and using a repro chassis of the same dimensions does not solve on of the amp's biggest problems, heat.

I have heard only good things about their products and if I were looking for a new or even thinking about modding something, this amp would be on my short lost.
Don Brian Levy, J.D.
Toronto ON Canada

 

First, posted on April 14, 2014 at 06:43:31
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 I should have said "Nice active link to ebay" in reply to your original post! Thank you.

Steve O and Flyquail have explained the hum pots nicely!

As for omitting the tone controls, etc. Some people want a re-issue to be as close as possible to the original. Changing too much might cost them sales, since it wouldn't be considered an SCA-35 anymore.

If you have a ST-35, I strongly suggest you consider the EFB modification. It doesn't eliminate the 7199 in the SCA-35, or the 7247 in your ST-35. What it does is change the cathode bias of your amp to an "enhanced fixed bias". By doing so, it improves the power output, lowers measured distortion, and the amp sounds much better.

You don't have to buy some kit, or boards, etc. The few parts necessary should cost you about $5, and greatly improves the sound of the amp. I haven't read one negative comment from anyone who's done the EFB mod. Edit: Which includes me, hearing the improvement to my SCA-35 after switching to EFB.

The specs shown are from a SCA-35, but the improvement will be the same for the ST-35.






 

RE: The Dynaco SCA-35 is back!, posted on April 14, 2014 at 09:18:41
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 Nice! However, I don't have $1K burning a whole in my pocket. I do have a working, all original (except for the diodes) factory assembled SCA-35 that I paid $35 for quite a while ago. I still can't decide what to do with in. There are not too many virgins left! Fare more interesting to me are the available parts that this company is also supplying.

Dave

 

RE: The Dynaco SCA-35 is back!, posted on April 14, 2014 at 11:22:44
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi guys,I haven't yet passed my Heathkit DC electronics course yet even though it's been sitting on my wire rope spindle coffie table for over 20 years. So I'm always looking for answers,and I appreciate all your help,I mean it. But I must quote someone and you guys can debate it because your way smarter than I. I asked this question on another site 3 years ago. What do the hum controls on the back of the Dyna SCA-35 really do? I thought they set the power tube bias,I didn't know. Frank VanAlStine gave me this answer: The hum control simply interjects power supply hum into the output,out of phase with the output hum,a kind of 2 hums are better than 1 scheme. The circuit conditions that cause the hum are still there, just masked. Not a good engineering solution. Also in his Audio Basics newsletter,free on his site, I subscribed back then, he explained the plight of the 7199 tube,being noisy and rare and such and he used the word (unobtainium). I don't know who coined it,and I don't care but it's dated and inwriting. I'm not trying to be stir up the nest, I just wanted to share some facts I learned 3 years ago and in 1982 (Audio Basics). Thanks I love you guys but had to get that out of my system.....Mark Korda

 

I built an SCA 35 in the '60's and was sorely disappointed with it!, posted on April 14, 2014 at 12:23:32
spindoctor
Audiophile

Posts: 1661
Location: Virginia
Joined: December 31, 2002
 The sound was dark, the power was less than ideal and it ran incredibly hot. I believe my wife ultimately sold it at a yard sale before one of our moves. No regrets.
Sim

 

I don't blame you, posted on April 14, 2014 at 19:13:54
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 I listened to several SCA-35s back in the late 1980's, and they sounded like a wet blanket had been thrown over the speakers. This was on a pair of Quad ESL 57, and Altec 604. My friend bench tested them (one was his, the other mine) to make sure they were working correctly. They were. Ugh! I let mine sit for about 15 years, with no desire to listen to it.

That's why I recommend the EFB mod. It took my SCA-35 from "wet blanket" to a very listenable amp. No, it didn't transform it to a SET, but what a great improvement for $5 in parts!

I only wish I was at your garage sale, because the SCA-35 has what are considered Dynaco's best output transformers. They can be used to build a very good 6BQ5 amp.

 

RE: I don't blame you, posted on April 14, 2014 at 20:17:00
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Shovel, that was an awesome mod project you shared.Thanks so much....Mark.

 

RE: The Dynaco SCA-35 is back!, posted on April 16, 2014 at 08:33:48
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 I don't think it is all that controversial. I think there are few here who would doubt Frank VanAlStine's technical qualification or knowledge of Dynaco. I have one of his early Super Pass modification of a Dynaco PAS preamp, and it is very well thought out and executed.

By introducing the hum out of phase, they cancel each other out. It would be better to have a hum free circuit, but canceling it out is better than nothing.

7199's are rare and expensive. It is a fact for a lot of tube types. You can substitute a 6GH8A with a rewire or adapter, but they are getting harder to find too. There are also new boards that change the circuit to and ST35 type, but use more available tubes.

Dave

 

Why? (nt), posted on April 18, 2014 at 05:11:49
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 nt

 

RE: The Dynaco SCA-35 is back!, posted on April 21, 2014 at 08:51:11
BillH
Audiophile

Posts: 3913
Location: Baton Rouge
Joined: December 23, 1999
 I didn't notice, thanks. This was my first amp, built from a kit (ordeal for me, as I had no experience and couldn't solder any better than I can caulk today).
This version seems nice, but why the cheap, cheesy connectors on the back?
They aren't nostalgic, and seem out of place on a thousand-buck kit.

 

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