Dyna SCA-35 or ST-35 rebuild? Your advice?

Dandy

Addicted Member
A while back I posted that my SCA-35 had a hum problem and the consensus is that it was because of unmatched power tubes. I have a matched quad on order, but meanwhile the amp has suddenly gone very soft in one channel and will not bias at all on that side. So that may be the underlying cause, which now needs to be sorted.

I got this amp in a messed up non-working condition with an old, disconnected preamp board, Chinese clone main boards and a powersupply board from Audioregenesis, pre EFB.

I went through the amp carefully with help from here and very kind help from George Ronnenkamp and added a P2P EFB mod. I am now thinking of doing a complete rebuild using all of Dave's nice SCA-35 replacement boards. I like the controls and compact phono stage, but I hear such good things about the ST-35. Should I just make it into a ST-35 instead?
 
My suggestion ( for what it's worth ) : Keep it as original as possible. There are no more
made. ST-35 on the other hand is available both at unmolested originals and brand
new as kits.
Thus keep the sca35 and use until you can buy a st-35. Don't destroy a uniq piece of history!
 
I'm on the flip side. Harvest the transformers and build a Stereo 35. Sell the remaining parts to someone who might want to build an SCA35. While the SCA35 is not a bad integrated by any measure, it is nowhere near as good sound-wise as a Stereo 35.

-D
 
If the original boards are missing then there is nothing unique left to save. Go ahead with your plan. I am currently nearing the end of a rebuild of a SCA-35 chassis which was stripped of xformers, tubes, faceplate and power cord. I am using Dave's boards for the rebuild (tronola.com) as well as Dynakitparts.com transformers. If you decide to go the ST-35 route take a look at Bob Latino's offering at http://www.bob01605.50webs.com

Either way good luck.
 
Thanks for all the thoughts. They really help when you find yourself talking to yourself!

I sympathise with Peterh's restoration view, and have taken that approach with my Scott 222C. But this chassis has already been badly hacked up at the back, so it will never win a beauty contest, and because Dave's EFB mod is so well-respected a modern restoration seems a good midway. The front plate, knobs, cage etc are good and it's nice to be respecting the original purpose of the amp as a compact integrated.

So, I'll probably restore it, but maybe I should saving for a ST35?! The iron is expensive to ship in.
 
I bet sonically great though!

I thought shipping was more to the UK , but it looks like medium rate Flate rate shipping (under 20 lbs) is $63 USD and maybe the seller may add delivery charge to the USPS. But maybe VAT etc. gets you like our taxes in Canada.

These Z-565 copies should be a good OPT for the $ and they have a great rep.
Really affordable also. Note they offer Two different secondary outputs.

For the PS trans maybe you can find something affordable over there and diy chassis or even look at what diytube's version. Maybe look for a higher rated (mA) or do mono blocks with the stock rated trans for cooling running (longer life) and probably better sonics as you should get better headroom.

http://transcendar.com/3.html
 
Thanks for all these further thoughts. I really appreciate the chance to think about both options. I'm leaning towards a nice rebuild of the SCA-35 and a separate build of an ST-35 clone later. I like the simple layout and design of the ST-35.

Getting a suitable PT locally would not be hard. Those transcendar OPTs look really nice Shadowdog! And the Triode ones come in at just a little less ($140). I wonder if anyone has compared the two?
 
Occationally used st35's are seen on ebay.co.uk , they will have 220 mains transformers
and you don't have to pay for customs and expensive shipping. You need the mains transformer
PA-028 ( the domestic PA-774 has only 120V AC )
 
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I guess i'm in the minority, but i'd leave it as an integrated. It really is a nice little amp rebuilt to spec with EFB. Let me ask? Do you really need a 17wpc power amp for something in particular? If so do the PA. If you like the all in one keep it whole. Mine has been out on lone for better than a year now which makes me happy because the person with it is enjoying it and it likely would be sitting on a shelf here (next to 4 other tube integrateds not being listened to )making me question my sanity. I hope that helps but looking back probably not.
 
Thanks nj. I must admit, like many tube AKers, I enjoy building amps and learning by doing. I always wanted to hear one of the EL84 Dynas, and so was very happy to find this one, even in poor condition.

I've now decided to rebuild it as a SCA-35 and have ordered all of Dave G's boards. Watch this space ... or not if you've seen it all before. :) Thanks for all the help in making the decision.
 
Maybe I'm a sucker but I find myself following everybody's builds and restores. Yours won't be the exception. Enjoy!
 
Good choice, I did the same thing. I think you will be pleased. The other thing I did was bypass the tone controls. There are instructions online to run them through the high filter switch to be able to switch them in and out of the circuit. Taking them out of the circuit gives you significantly more volume and headroom.

Good luck! I will watch your progress.

Thanks nj. I must admit, like many tube AKers, I enjoy building amps and learning by doing. I always wanted to hear one of the EL84 Dynas, and so was very happy to find this one, even in poor condition.

I've now decided to rebuild it as a SCA-35 and have ordered all of Dave G's boards. Watch this space ... or not if you've seen it all before. :) Thanks for all the help in making the decision.
 
I have too but you really aren't getting more gain, Just more gain in the first part of the volume knob. i was under the same impression but Dave Gillespie set me straight. If you go that route i can probably get you the info
 
When you put together your parts list for the boards you will need to add 2 100 ohm 0.5 watt resistors to the list. They are needed for jumping between pins 8 and 9 of V6 and V8 of the PC-10A boards when installing the capacitor board with EFB.
 
I think to do tone bypass and match the stock gain you need a 4p2p switch that fits where the high filter switch was. It involves having a resistor in series with each signal and another shunting each signal to ground . If you opt that way I'm sure I can come up with exact mod with the circuit and resistor values. I will say mine was pretty flat with tone controls centered and bypassing made little difference. Doing it with just the double pole switch adds a lot of gain early. So switching it in makes amp louder at same volume level and seems more detailed ( but its just perception).
 
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