This Dynaco SCA-35 is an integrated tube amplifier that any headphone enthusiast could appreciate. This is not only suitable as a headphone amplifier, it is a stereo integrated amplifier rated at 17 watts per channel. Classic Valve Design - Dynaco Clone and Original Design Boards. Home About Us News & Updates Build Showcase Services & Rates PCB's & DIY. We are now carrying boards for the SCA-35! Manual and instructions for the line stage. Legacy instructions for the phono stage.
I it's anything like my Dynaco Stereo 70, I believe it is it's one killer clean amp. These reproductions of Dynaco experiments proved very successful, have won fans worldwide of the amp listening 'Elite'. I too have seen many fine amps like McCintosh in use, Dynaco tube amps are the Bees Knees in butter. I've been using the 70 since the 70's. Had many amps come and go. My buddies had great reverence for the amp. I was getting this great sound on the guitar with 12' speakers, the organ sounded fantastic through the 12's, Vocals through the Dyna.and 12's.oh rich complex mids, bass definition we tested amps.talkin bout a super sparker.
Like beyond.I know this band I used to love to listen through that used McCintosh for PA power stage amps for stringed instruments.here I am talkin tube trash again! As long as you're not expecting a gainy class A/B type sound, and love warm, rich sounds, expanded dynamic range etc etc etc makes the boxes all sound way different than my MkII for instance I would say you'ld be loving to having a Dynaco amp product around. 35w is a big round sound!
I went through something to rebias it for 120v. Some of the older amps like this were designed for the lower voltage available at the time from any wall outlet 110v. Running it at the higher voltage after reads on the subject caused the 7199 tubes in the pcb to fry the pcb. I rewired the entire front end, then had extensive re-bias work done to it, and added a cooling fan plent o room.However I understand all this except maybe the fan was completely unecessary, the way to do it is reduce the voltaqe coming in at the ac line that goes to the wall outlet.I understand resistors will do this but AFAIK using more than one somehow to increase heat dissipation. Could be 64's were running cool enough.I saw a place where you can get aftermarket PCB's. Upon glance inspection my PCB was buckled, discolored, etc. They are not hard to work on, especially if the manual w/schem is there.
Actually the amp, and amp literature helped me with early electronics diagnosis learning. I don't want to scare you off.these things need work FTTT. I've changed tubes once since the late 70's, and I don't think it was even necessary at that time.80's.
These transformers 440A's Stereo 70 and other Dyna's are known for being overrated and 'indestructible'. I would put a beat output tube in one side, turn the bias up on it to 'medium fry' cause it to glow orange, and get melting tube tones.harmonic feedback pitch shifts, octave's?' Down etc.ultra cream.'
Till the tube innards became so malleable that they warped and melted to death.awesome!!! Once the tube got to Med fry temp., it would last only about 20 min max though. Neat way to get the last big kick out of an otherwise diminished output tube.
I had the cooling fan in there.the output tubes sockets are in frame holes.proceed at your own risk.probably not recommended for maximim amp life.lol. Actually the 70 has those 7199's in pentode config like AC 30 I read, this boosts the preamp input even more than 'normal' and lets the amp work at about 30% vol with the guitar plugged straight in. I wasn't going to mention this it's in contradiction to an earlier post about not amp hacking on Dyna's.the bottom end I read is easy to tighten up.I would be guessing try ampage 'they rock amps' there. and is a fairly common mod for using these as musical instrument amps. Getting one of these going is not always plug 'N play.however a 'right' working one is well worth the trouble.IMO. Finding a tube amp that is exactly what you want it oto be can be this way or pricey.I had to fit a side ways cap 'in the basement over the bottom under the pcb.I couldnn't find the original' replacement for the big double cap. When ' I had dude' work on it he found the part to mount in the original way though.
One of the big differences between Dyna's/Mac's and other amps is the transformers. Being highest quality hand wound.they have very even response to a wide band of freq's and don't tend to cancel any of them like an Iron with overlaps or gaps in the windings. That and the fact that these Dyna experiments ckt turned out to be very well liked. Can be 'some messing' to get one working properly and the way you want.but once you do you'll be going uuoohhh Yeahhh.that or.Find a Matchless for cheap lol. I read a review in guitar player 'Big amp shootout' and they did a part on the new Vox amps nothing Vox was available for the fifteen year period of contracted Thomas distributionyerx anyway the old ones had better Iron according to the review.louder and more responsive.
Introduced 1964 17.5 watts per channel four 6BQ5 power tubes two 7199 drivers two 12AX7 in the preamp This belongs to my dad. It's been sitting on a shelf for years.
I powered it up and of course it sounded bad. It had an annoying hum.
I replaced the can caps in the power supply with SDS board, built it up myself to save some money and use larger value caps. Cleaned it up a little. Replaced some of the coupling caps with parts I had laying around.
I need to order some resistors and caps to finish the job. Took me 4 nights to finally get it installed and working. Ran into some problems but got it straightened out. Now the hum is completely gone! Been listening to it all morning and it is a very cool, clean little amp. Can't wait to do some tube rolling on this thing.
Sushimaster. In the 80's, when I was real small he bought a Marantz 7 at a flea market in California for $5. A few years later, he sold it to a guy here in Houston for $300 because he didn't know he had a 7c.
Later he found out the 'c' stood for cabinet. He sold the same guy his Mac 240, his Mac 75 (one channel), a bunch of Dynaco ST70's, and a HK Citation tube power amp II for a few hundred each. He threw away in the trash an AR XA turntable because he thought it sounded like junk. When his Audio Research 75 tube amp stopped working, he threw it in the garbage. Same goes for a pair of AR3A speakers that probably had the pots go out. This was all before the internet, where people now can find all the information on these things and how to restore them. I think he threw away or donated some Scott and Fisher tube amps too.
It pains me to think of all the great stuff I could have restored but now costs and arm and a leg. All the gear he purchased real cheap at flea markets back in the early 80's when people didn't know what this stuff was or how much it was worth, including the Audio Research 75. But luckily he kept a lot of his Dynaco gear that I like and can now restore. Just thought I'd share this nice little history. Sushimaster.
Made by Audio Technica.I found these at Goodwill, I wanna say 6 bucks or something real ridiculous.I usually keep the price sticker on these things so I can shock my friends with how much I paid for them. The surrounds were rotted. I refoamed it and was planning to sell it but they are so convenient because of their small foot print.
I find myself using them for testing amps that I restore and they are so easy to move around. The tweeter is a bit bright however and it's Acoustic Suspension design makes it low sounding for most amps. Sushimaster. Update: well the left channel went out again. I thought I had fixed it when I replaced a suspicious coupling cap on the PC board. It was making music for less than 1 day. Then I turned it on this morning and heard a crackling noise on the left channel, then poof.no sound in the left.
I swapped the tubes so I know it's not that. Sometimes when you repair something like the power supply, it will cause something further down the chain to fail especially on old tube equipment with 50 yr old parts. Waiting on new resistors and caps from Digikey.I'm just going to change out every part on the motherboard. Sushimaster.
Here's a pair of my Dynaco Mark III tube monoblocks that I'm using right now. I have my squeezebox plugged directly into them (no preamp). I bought this particular pair off eBay a few years back and of course it needed restoration but the cosmetic was pretty good for its age. I again used the SDS labs cap board to replace the can cap. New metal film resistors on the driver board.
And a new qaud set of SED 6550 to finish it off. Introduced 1957 60 watts two 6550 or KT88 one GZ34 rectifier one 6AN8 driver - Sushimaster. The Mark III's IMO sound good even with the original coupling caps in place. From my understanding, coupling caps and tubes affect the tone of the amp. Resistors on the other hand mostly make it less noisy and not so much affect the tone. I would imagine, that if you change the coupling caps to something more modern like Teflon V-Caps, then the Mark III would sound more like a modern amp. But I haven't verified this.
I thought about replacing the coupling caps at first with something more modern, but then I also wanted to hear the system with as much of the original parts as possible to form a baseline. Then maybe later down the road change/upgrade the caps, but surprisingly I like these original caps so I may just stick with them.
I also think the original coupling caps enhance the vintage sound. But at the same time, I don't have any other 6550/KT88 tube amp to compare these to. I did have to use modern metal film resistors because I encountered intermittent noise on the driver board and I thought maybe that would resolve it. Some of them were out of spec, so I changed them all. Of all my current tube amps (ST70, SCA 35, Mark III, Conrad Johnson CAV50), I like the Mark III's the best (but don't get me wrong, I like them all). It's the most tubey sounding of them all (YMMV).
It makes the CAV50 seem Neutral even though I know it's not. Then again it could be I just prefer the 6550 tube type. I'm not sure.
Sushimaster. Update: well the left channel went out again. I thought I had fixed it when I replaced a suspicious coupling cap on the PC board. It was making music for less than 1 day. Then I turned it on this morning and heard a crackling noise on the left channel, then poof.no sound in the left.
I swapped the tubes so I know it's not that. Sometimes when you repair something like the power supply, it will cause something further down the chain to fail especially on old tube equipment with 50 yr old parts.
Waiting on new resistors and caps from Digikey.I'm just going to change out every part on the motherboard. Sushimaster. That's the thing with really old tube gear.it could be anything or nothing at all. On my dad's PAS preamp, I had replaced the cap board with SDS labs. Then, sometimes it made sound, other times nothing. I checked every solder joint, double checked and triple checked all my connection (thought maybe I made an error), replaced all the tube.spent all day troubleshooting it with my multimeter, it almost drove me to the breaking point where I wanted nothing more to do with fixing vintage tube gear.
I told myself after this, I was going to buy only modern tube gear from now on. Turns out it was a bad tape/input selector switch. When it was engaged 3/4 of the way, it made contact and there was sound. Push it all the way like it is supposed to be, and there was nothing.and I discovered this by pure luck. It may very well be tube sockets and it might not.
But the thing is you change some things and start the process of elimination. Sushimaster.