Dynaco SCA-35 project "Start-Me-Up" with EFBâ„¢

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Dynaco SCA-35 project "Start-Me-Up" with EFB™

Postby Dynaco_WJW » Sat Jun 11, 2011 12:50 pm

Dynaco SCA-35 project "Start-Me-Up" with EFB™

Last week the new power board with EFB (Enhanced Fixed Bias) arrived from Canada from http://audioregenesis.com
This board is meant for a Dynaco SCA-35. Funny detail is that I am one of the first of getting this board. You will see a photo coverage of the process of rebuilding a Dynaco SCA-35. The amplifier will be provided with new boards from Audioregenesis. The preamp board PC-11, a complete new power supply board which will replace the both can capacitors but with a extra feature!! EFB !! and the PC-10A output board in stead of the PC-10. The PC-10A is using 6GH8A or 6U8A. These have the same quality as the rare and expensive 7199 tube. The biggest change will be the extra feature EFB. If you want to read everything about this, just visit http://tronola.com/A_New_Look_At_An_Old_Friend.pdf

First I had to make a choice which SCA-35 is most suitable for the new boards. I have 4 SCA’s with one already with new audioregenesis boards (exept the EFB but with PC-10 boards). My choice was to pick the SCA with the best looking chassis.

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This one is ready for restoring. The original pertinax (pressed paper) boards are a bit discolored because of the heat of the tubes.
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The bottom of the circuit board was a bit a mess.
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The new PC-10A boards are in place, the old stuff besides it.
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At the output tubes it is becoming crowded already.
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To connect the wires for the input selector takes a bit more time! Lots of spaghetti on a square cm.
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This is the new Power Supply Capacitor Board with EFB™ . The board has double layers and the holes for the wires are full metal throughout the hole. The screws for attachment are already there. The manual is sent with the board, and very good I must say. If you want to see the manual for this board, visit http://www.audioregenesis.com/manuals/pdf/SCA35-CAPR05_Installation.pdf
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This is the bottom of the can capacitors. One of these capacitors is not available anymore. The other one is, but sending it to the Netherlands, Europe is very expensive. In fact a complete power board with EFB is almost cheaper. ;)
If you want to read more about David Gillespie's EFB™, go to http://tronola.com/A_New_Look_At_An_Old_Friend.pdf
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Fine, these are gone. Two yawning holes stay behind.
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The new power board is placed within a minute, it fits just perfect. Connecting the leads can start.
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Everything has finished! I check all the wires again. With a magnifying-glass I even check the soldering. This is a good thing when you use the old wires again. I partially renewed the wires.
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Now I can put in the new tubes. I have new matched EL84 from JJ and the 6GH8A are RCA. The preamplifier became the old 12AX7. Give pressure to the bottom side of the boards when you put in the tubes! Isn't it a fantastic view?
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Now I can connect it to 'the grid' and set the right bias on the power board. This is possible with the decent test sockets. The average voltage for left and right channel has to be 0,27V what is a bias current of 27mA. The original design has a bias current of 35mA. The power dissipation is lower and thus extending the lifetime of the tube. A new (extra) feature is using an EFB modified ST-35 or SCA-35 as a pseudo tub tester to match output tubes for bias current. The EFB circuit makes this possible, it would not work with the stock, cathode bias circuit. As I understood, there will be a procedure for that soon!
A CD of the Rolling Stones is lying ready to play with the song "Start Me Up" under the play button. On the multimeter you can see the voltage 0,27V.
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The cover can be attached! Listen to some music :))

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How does it sound? I will report in the next post.
Excuse me for my bad English language
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Postby Sal Brisindi » Sat Jun 11, 2011 6:15 pm

Excellent job on your SCA-35. Looking at the photos of your setup, you have some very mint looking Dynaco's.

Regards,
Sal
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Postby Dynaco_WJW » Sun Jun 12, 2011 6:01 am

Sal -- Thank you very much. To be honest, the actual work was already done by Audioregenesis. I'm very pleased with the circuit boards. It took only a few hours of work. The leads for the filament is maybe the most work. When I bought this SCA-35 I discovered that the balance pot was not the original one. These where specially made for Dynaco. Last year, during holidays in France, I found a original balance pot on the Internet. To replace this pot with the wrong one was maybe the most of work because of the little space behind the front.

Yes they look mint, but some of the chassis have some corrosion. These chassis are cadmered and that is forbidden right now. (only accepted for aviation). It is possible to nickel plate it, like Audioregenesis did, but then you will have to 'silkscreen' the text again. I don't have any experience yet in silkscreening. But, someday I will do a complete restoring for the one with the most oxidated chassis. FIY, there is rust-stripper from Rust-o-leum that 'eats' the corrosion from a cadmered chassis. http://www.youtube.com/watch?v=-n8-vY7OBaQ

My next project is restoring a ST-35. I think I will do a new post for that. I want to make the EFB on that amplifier too.
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How does it sound.... the comparison

Postby Dynaco_WJW » Sun Dec 04, 2011 1:48 pm

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Test report in progress....
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THE TEST RESULTS

Postby Dynaco_WJW » Mon Dec 05, 2011 3:23 pm

In this test report I compare two fully restored Dynaco SCA-35 amplifiers. One employs the new Audioregenesis *EFB capacitor board and PC-10A (6GH8A) output boards, and another uses the more conventional AR capacitor board and PC-10 (7199) output boards.

*EFB (enhanced fixed bias) is a concept developed by Dave Gillespie to increase the power, lower the distortion, and prolong output tube life in Dynaco SCA-35 and ST-35 amplifiers.

Music Source: Sony CDP-303ES CD player.
SCA-35 EFB Amp. PC-10A Tubes: RCA 6GH8A, JJ EL84 (matched quad)
SCA-35 Conventional Amp. PC-10 Tubes: RCA 7199, JJ EL84 (matched quad)
Speakers: Rauna ‘Opus 3 Chaconne’ (Sweden) 90dB sensitivity

The program material I chose for this test was from the Rolling Stones ‘Still Life’ remasters CD, and in particular, the ‘Start Me Up’ track.

The tone controls for both test amplifiers were set to the flat position and the volume controls set at 55%.

Listening Test Results:
I listened to the ‘Start Me Up’ track on the SCA-EFB about 20 times, then immediately switched the cables and speakers to the ‘conventional’ SCA-35 which had been on and fully warmed up. Upon playing the track again the first thing I heard, or rather did not hear, was the ‘depth’ exhibited by the SCA-EFB. The sound didn’t surround me any more, it was just there in front of me. The ‘s’ sounds were noticeably less clear, which I found somewhat disturbing. The cymbals seemed to be absent and overall it sounded somewhat ‘muddy’. Compared to the EFB version, the conventional SCA-35 is just less enjoyable to listen to, and it’s as simple as that.
I then switched back to the SCA-EFB. The bass was more solid, and overall just a smoother, cleaner sound. The room was again ‘filled’ with music. The vocals and ‘s’ sounds were more natural. The most significant improvement, I believe, is that it is much more pleasant to just ‘listen to the music’. At the end of the track, the clarity of the shouting crowd is nice to hear, but with the conventional SCA, it was just not as pleasant to listen to.

Conclusion:
For me it is clear, the new Audioregenesis EFB capacitor board was a very good choice for upgrading the SCA-35. I will continue testing with other program material, and perhaps another report to follow.



Image
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Postby dcgillespie » Mon Dec 05, 2011 8:14 pm

WJW -- Thanks for taking the time to report your listening impressions. I believe they mirror quite accurately those impressions that others have reported as well.

While I didn't go into nearly the detail you have, I summed my impressions up as the amplifier being much more dynamic and having greater overall clarity.

The execution of EFB(tm) on the Audio Regenesis power supply board is very well done. I'm glad you have found it to be such a worthwhile effort with your amplifiers -- both of which look very nice indeed!!

Dave
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Postby nyazzip » Tue Dec 06, 2011 3:07 am

...now if there were only Diytube ST-35 EFB boards available.....! i don't think i'm brave enough to cut my traces up on my "rev D", especially since they seem to be unavailable now =:o
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Postby Dynaco_WJW » Tue Dec 06, 2011 10:00 am

dcgillespie -- Thank you very much. I repeated the test with a song from the album 'On the Road from the *'Eelco Gelling Band'. Song #5 Travellin' Man was my test song.

This song contains, voice, drums, guitar(s) and Hammond organ. The results are again the same. This time power was set to 95%.

The difference is most remarkable when switched over from the conventional to the EFB amplifier.



* Eelco Gelling was together with Jan Akkerman one of world best guitarists in the seventees. He toured with Eddie Boyd and Alexis Korner. In 1966 they toured with John Mayall. link: http://en.wikipedia.org/wiki/Eelco_Gelling
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Postby steady » Thu Dec 08, 2011 8:28 pm

Dynaco_WJW

Great post, pics and review of the performance of the AR package.

I just confirmed yesterday with George at Audio Regenesis that my SCA-35 driver and preamp boards have been shipped (for my early Christmas present). My work-in-progress is running Dave's inspired EFB mod from AR and exhibits that same clear dynamic that you describe. Unfortunately is also suffering from some significant hum which I am sure that George's upgrade/new tubes will clear up. I will likely rewire and refresh some other parts of the old warrior while I am at it.

Any more mods in the works ... new volume pot or tone bypass?

Can't wait until you do your ST-35 project.

Cheers

Dave
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Postby Dynaco_WJW » Sun Dec 11, 2011 3:49 pm

Dave - Thank you very much for your compliments, and congratulations on your purchase of the remaining Audioregenesis boards to complete the SCA-35 set. I understand you already had the capacitor board with EFB. I always like to renew all the boards to avoid the possibility of degraded performance, or reliability problems, with components that are over 40 years old. I like the Audioregenesis boards because of the professional quality and technical support. I also purchased new tubes for the both the preamp. and output boards. This way I can have confidence that everything will be OK. I have never had any hum problems, and my amplifiers are built and wired as shown in the original manual, other than the minor modifications required for the EFB feature. I did not find it necessary to resort to additional shielding, etc. I think the original Dynaco engineers knew what they were doing. Hum can be caused by a number of things, like improper wire routing, a bad ground, aging tubes or components, and such. With all new boards, good tubes, and following the manual for assembly, your hum problem will likely be solved. What type of tubes do you plan on using in your restored SCA-35?

As for the volume control and tone control bypass, I have no plans at present to change or modify these. They seem to be working well in my amplifiers. Note that bypassing the tone controls in the SCA-35 is a little more complicated than you might think. To do this properly you would need a 4-pole switch, and an attenuator of about 18db should be inserted in place of the tone controls when bypassed to avoid a drastic increase in volume and volume control sensitivity. It is important to set the tone control pots. exactly described in the manual to obtain flat response at center, and when set properly they do not significantly degrade the performance, so I just leave them that way.

On my ST-35 project, I still need to build the EFB. I was thinking of making a heatsink which could be attached to one of the bolts of a transformer.

Good luck with the installation of your new Audioregenesis boards. You will have a very nice amplifier when completed. Please keep us informed on the progress, and how it sounds. Pictures are always welcome.

Best regards,

Wim
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Postby steady » Sun Dec 11, 2011 4:24 pm

Thanks Wim

I will post pictures when it is completed.
George clued me in on the challenges of bypassing the tone controls. I think I will wait until the new boards and tubes are in.
Good luck with the ST-35 and once again, great job with the SCA-35.

Cheers ... Dave
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Postby Shannon Parks » Mon Dec 12, 2011 7:27 am

nyazzip wrote:...now if there were only Diytube ST-35 EFB boards available.....!


Hopefully very soon. I had hoped to have some prototypes done by Christmas, but another project has zapped my time. Working with Dave and plan to have it be exactly the same footprint as the Rev C and Rev D (for easy swaps). Rev EFB?

Shannon
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Postby nyazzip » Mon Dec 12, 2011 10:58 pm

how about "Revision E.1 EFB"
i am totally onboard with this and i would definitely purchase 1 and probably 2.
i was out earlier tonight and talking to some young vinyl music afficionado, and i tried to sway him into building a tube amp kit...he seemed intrigued. i wish someone had talked me into it when i was young; i missed out on a lot!
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Postby DerekVa » Wed Jan 18, 2012 1:00 am

Shannon - just a suggestion / impassioned plea - while you are at it (making the new Rev.E.EFB boards) - make a stand-alone EFB board as well, so that those folks with earlier revisions can retrofit EFB into their Rev.D or earlier ST35.

Pretty please with sugar and cream on top? O:)

-D
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Postby Shannon Parks » Wed Jan 18, 2012 6:36 am

But isn't that the Audio Regenesis board already?
http://audioregenesis.com

I would make the board the same dims as the Rev C & Rev D, so a retrofit would be easy.

I'm in the bowels of a commercial Budgie project. It basically has absorbed all my tube time in the last several months. But the revamped ST35 is on my short list of 2012 projects.

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