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Old 23rd May 2012, 09:29 PM   #111
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You might want to look here. CurcioAudio.Com - DIY Vacuum Tube Audio & Dynaco Repair Restoration Upgrade to a Pas3 design and then mod it with Joe's modification. Easy straightforward with great instructions.
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Old 23rd May 2012, 11:27 PM   #112
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mr2racer.
Do you mean this " http://curcioaudio.com/Dynaco%20PAS%...tion%20Mod.pdf " ?
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Old 27th September 2012, 02:04 AM   #113
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Yes tofsound that's what I did.

I have some questions if anyone can help? I wanted to use DC for the preamp filaments in the phono section and for the 12DW7 preamp tubes in the output section. (I'm using ST35 boards.) There wasn't enough amperage to simply use one winding for the preamp and one for the outputs. So I paralleled the two windings and then split them to run AC to the EL84's and built a rectifier for the preamp tubes. Also, I removed the 'hum adjust' pots. The question is should I use a ground after the last tubes? Ala PAS3 and ST35? Or put the pots back? I also intend to use Dave Gillespie's EFB biasing system.
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Old 27th September 2012, 02:51 AM   #114
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The classic recommendation is to bias the heaters up to about +25 volts DC, or the factory original way of biasing up to the output tubes' cathodes. You'd only need one of the original hum pots if you wanted to try trimming. And why not? You've got the thing right there!

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Old 6th October 2012, 10:08 PM   #115
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Hey All,

I powered up my SCA35 last night and the power tubes are wide open. Dave Gillespie's circuit shows the middle leg as the adjust terminal. The LM377T shows the left terminal as adjust. Which is right? Is Dave labeling the terminals differently?
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Old 7th October 2012, 04:18 PM   #116
ArtG is offline ArtG  United States
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The correct device to use in this application is an LM337 not LM377. (typo-?)
In the TO-220 package, from the front with the tab facing up, the leads are numbered 1/ ADJ, 2/ INPUT, 3/ OUTPUT. If you wired the regulator otherwise, and powered it up, I'd consider replacing it.
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Old 11th October 2012, 02:27 PM   #117
rhing is offline rhing  United States
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I thought I would chime in here. I restored and modified my SCA-35 using modules from Audio Regenesis. Some here might feel this is not "true" DIY, but I just wanted high quality components in my rebuild since I was going to put a lot of time into restoring this amp. This amp in stock form wasn;t in the best of shape and needed new boards anyway.

Dynaco SCA-35, 5.jpg Dynaco SCA-35, 7.jpg

I purchased the power supply/EFB module with an implementation of Dave Gillespie's EFB circuit. I've implemented the EFB mod on my Dynakit Stereo 35 power amp, and it was a great improvement, so I knew that I could get great results on implementing the same on an SCA-35. Moreover, the Audio Regenesis module is an elegant solution combining the EFB circuit with better power supply capacitors.

I also purchased the PC-10A and PC-11 amplifier modules. I modified my phonostage board according to Adrian Chan's post on Audio Asylum:

Re: Dynaco SCA-35 phono input stages - Adrian Chan - Tubes Asylum

This is basically an adaptation of Joe Curcio's modification to the PAS3 phonostage. Further improvements included shielded Beldon plenum cable and Mil-Spec Copper wire, a new set of tubes including a pair of Sovtek 12AX7LPS tubes from Jim McShane. I added a few of my preferred caps and resistors here and there to my liking. I put a ton of work into cleaning up the chassis, reconditioning all the pots and switches and rewiring the unit.

Dynaco SCA-35,13.jpg Dynaco SCA-35,15.jpg

For my analog front end, a friend donated a Kenwood PC-400U belt/idler wheel drive turntable. He bought off a seller from eBay who didn;t properly pack the turntable and the acrylic cover was shattered into multiple pieces. The turntable itself wasn't too bad, and needed some care to bring it back to life. I focused on restoring the drive system, and fabricated new thrust bearing plates for the main bearing and the belt/idler wheel pulley bearing. I also rejuvenated the rubber on the idler wheel with MG Chemicals Rubber Renue compound. I polished the bearing shafts and sleeves as best as I could and then applied Honda Molybdenum grease to the main bearing and Shell Formula 5W-20 oil to the belt/idler wheel bearing.

PC-400U, 3.jpg PC-400U, 4.jpg

I installed a Shure M97eX MM cartridge on the table and properly set up the balance, alignment, and tracking force. Together with the SCA-35, this is analog heaven.

2012-10-06 09.44.38.jpg
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Old 11th October 2012, 11:49 PM   #118
ArtG is offline ArtG  United States
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You did a beautiful job on the SCA-35. I'll bet it sounds even better than it looks! Congratulations! BTW what's that odd looking unit on the shelf under the turntable? Doesn't look much like a Dynaco item to me!
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Old 12th October 2012, 12:41 AM   #119
rhing is offline rhing  United States
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Quote:
Originally Posted by ArtG View Post
You did a beautiful job on the SCA-35. I'll bet it sounds even better than it looks! Congratulations! BTW what's that odd looking unit on the shelf under the turntable? Doesn't look much like a Dynaco item to me!
You are correct. That is my Audio Research LS-7 line stage preamp. It's in mint condition and I bought it for $575 from an ARC enthusiast in the San Francisco Bay Area. She wanted to make sure that she was selling it to a caring buyer (s0 I guess I qualified). I use that with my restored and modified Dynakit Stereo 35 power amp. Eventually, I will have two complete systems with analog sources. I am in the middle of restoring and modifying an AR XA with a Grace 707 MkII tonearm. I'll need to build a suitable phono stage to feed the ARC LS-7. For now, everything is in the man cave, but the second system will go in the living room.
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Old 12th October 2012, 11:08 PM   #120
jgf is offline jgf  United States
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Wow, that looks great, excellent work! I'm sure it sounds great too, the EFB mod really transforms it. One question: Should those PECs (packaged electronic circuit) be on the phono inputs after the phono stage mod? I read those instructions, but it's not clear to me...
Quote:
Originally Posted by rhing View Post
I thought I would chime in here. I restored and modified my SCA-35 using modules from Audio Regenesis. Some here might feel this is not "true" DIY, but I just wanted high quality components in my rebuild since I was going to put a lot of time into restoring this amp. This amp in stock form wasn;t in the best of shape and needed new boards anyway.

Attachment 305843 Attachment 305844

I purchased the power supply/EFB module with an implementation of Dave Gillespie's EFB circuit. I've implemented the EFB mod on my Dynakit Stereo 35 power amp, and it was a great improvement, so I knew that I could get great results on implementing the same on an SCA-35. Moreover, the Audio Regenesis module is an elegant solution combining the EFB circuit with better power supply capacitors.

I also purchased the PC-10A and PC-11 amplifier modules. I modified my phonostage board according to Adrian Chan's post on Audio Asylum:

Re: Dynaco SCA-35 phono input stages - Adrian Chan - Tubes Asylum

This is basically an adaptation of Joe Curcio's modification to the PAS3 phonostage. Further improvements included shielded Beldon plenum cable and Mil-Spec Copper wire, a new set of tubes including a pair of Sovtek 12AX7LPS tubes from Jim McShane. I added a few of my preferred caps and resistors here and there to my liking. I put a ton of work into cleaning up the chassis, reconditioning all the pots and switches and rewiring the unit.

Attachment 305841 Attachment 305842

For my analog front end, a friend donated a Kenwood PC-400U belt/idler wheel drive turntable. He bought off a seller from eBay who didn;t properly pack the turntable and the acrylic cover was shattered into multiple pieces. The turntable itself wasn't too bad, and needed some care to bring it back to life. I focused on restoring the drive system, and fabricated new thrust bearing plates for the main bearing and the belt/idler wheel pulley bearing. I also rejuvenated the rubber on the idler wheel with MG Chemicals Rubber Renue compound. I polished the bearing shafts and sleeves as best as I could and then applied Honda Molybdenum grease to the main bearing and Shell Formula 5W-20 oil to the belt/idler wheel bearing.

Attachment 305845 Attachment 305860

I installed a Shure M97eX MM cartridge on the table and properly set up the balance, alignment, and tracking force. Together with the SCA-35, this is analog heaven.

Attachment 305846
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