SCA-35

[kurtbauer]

I did an SCA-35 rebuild that got out of hand (in a good way, I think). I used ST-35 amp boards, initially based on James Lin's article, replaced the selector switch, installed an Alps pot, took out the tone controls, used Sheldon Stokes' cap board, and ended up scrapping the phono board rebuild and inserted a Scott Nixon non-oversampling DAC in its place. As a result I had to bring in some add'l. DC power. So I ended up with digital as well as line level analog inputs.

If you end up looking for a phono board (and a bag of parts, BTW), I have one.

Have fun with your project. Let us know how it goes.

Kurt

[sorenj07]

Major update. I completely, thoroughly gutted the whole amp. Unscrewed and carefully unsoldered all transformers, drilled out the rivets for all the PC boards (damaged the phono board), unscrewed the faceplate, and threw out all the pots. I was feeling a bit OCD and besides, I bet I can wire it up more nicely than it came, with shielded wire etc.

My impulse at this stage is to bolt some perforated aluminum metal over the holes and point-to-point a new circuit, but there's really not much room under the hood for coupling caps etc. If I plunk in some ST-35 boards, which have a better reputation, the front panel becomes a bit weird if I don't actually include any tone controls. One option would be an active tone control circuit before the power stage:

http://www.angelfire.com/electronic/fun ... one-A.html
(the one labeled "Figure 14") At the cost of two 12AX7's, it seems like a pretty good one.

Tacking on a phono stage would be cool but I'm not sure the PT has the heater power to feed four 12AX7's..

Keeping the old chassis at this stage means drilling out more rivets, installing new RCA jacks and binding posts (disregarding the silkscreening), filing out an IEC socket, and installing new hum pots. Seems like a lot of work. I could replace the front panel with a piece of aluminum I get fabricated, maybe with some lettering engraved into it, but you can hardly call it a Dynaco any more...

Maybe I'll go to hi-fi hell, but I'm tempted to cut and run, and scratch build my own amp using the iron and tubes. I'll avoid all of the issues that come with salvaging what I can from the SCA-35. I'd use the PA774 with a pi filter, 3.3uF/5H 65R/470uF to put out ~340V B+, at 38mA/tube. I'd probably use an LTP with either a CCS derived from a tiny bolt-in transformer, or another negative voltage supply like in my most recent amp.

So yeah, I have a few options. Luckily I have some time to mull things over, and fix up my monoblocks. I might put them up for sale later.

[TomMcNally]

Sounds like you had some fun !

I'd suggest one of the diytube ST-35 boards and
one of your home made chassis. You'd have
a nice lil amp in a few hours. Sell it and
build your SET !

... tom

[sorenj07]

Hey. I would love to use the diytube board, but unfortunately I have a real thing about point to point, so if I'm doing a scratch build, I'd probably want to go that route. Plus I can try different tubes, and different topologies. I like to think that each amp is an opportunity to try something new.

Given that this is some of the best iron (for the that can be had for EL84/6V6 types, I'm considering actually selling the triode EL84 amp I'm using right now. I can put a triode/UL switch in the new one using Z565's. I love the chassis I'm using but I'd rather have something with a nicer faceplate and thicker aluminum that doesn't need oodles of aluminum angle and bolts to be stable! Yellow_Light_Colorz_PDT_07

[TerrySmith]

I did a rev. c board and used a SCA35 chassis. I took out the center section, got some 1/2 aluinum angle from Home Depot to tie the front and rear panel together. Then for a flat floor a Hammond 12x10 cover fits almost perfectly.

The circuitry was totally stock Diy-35.

[K-MAN]

I was just reading through this old thread and noticed separks said that the tone control bypass adds hum. I thought it would create less hum? Also does adding the choke to the power supply reduce hum or can it add hum with it's magnetic field?