More Questions re: Integration and Mallards

for the DIY ST35, the Dynakit and every other PP EL84

More Questions re: Integration and Mallards

Postby Bottlehead » Fri May 28, 2004 12:13 am

This is more stuff regarding my previous questions under "Integrating Baby Blue"--I don't mean to hog board space but I'm starting a new thread to keep it visible, I'd like some input from any double-E types.

Thanks to everyone who responded. Shannon, my current unit is a Rev B that's up and running but still in the tweaking stage and I was planning to purchase a C or D for this project--with the transformers re-arranged I would have room for a 9"x4" hole and could mount a Rev C with no problem.

I agree that the SCA35's stock tone circuits suck, but I had figured on using a stepped ALPS unit for volume control, replacing the PECs with hard-wired components if necessary (Dynaco bragged about these high-tech minicircuits) and rewiring everything with 20ga silver/teflon. The stock pots seem to be good quality after a liberal bath of De-Oxit. The input selector isn't the greatest but a fiberglass replacement is available. OR I could just bypass the tone circuitry altogether--the only reason I'd like to keep it is because it's there. The output connections from the pre-amp board lead to pins 4 and 5 of the easternmost EL84 for each channel.

I was hoping someone knew of a replacement board. Curcio has both line stage and phono stage boards for the Dyna PAS preamps, I assume that tapping into the PA774 PT wouldn't be a problem--I'll do some more research for future reference, but I'd like to keep the cost down and for now I'll likely try component-upgrading the original circuit as best as I can. I don't see how I can really go wrong unless I fry something expensive. The chassis isn't doing me any good anyway, and will serve well as a straight enclosure for Baby Blue if I decide to drop the "integrated" scheme--I'll just fabricate a new face plate and use the gold RCA's for another project.

I'm a simple self-taught tinkerer and if any of you engineering types have reason to tell me I'm an idiot I won't be a bit offended--in fact I'd appreciate it. My only major concern is that one of the OPT's will be tucked tightly between the preamp PCB and the input terminals (where the cans are now) and on general principles that's the last place I'd like it to be, but if I route things carefully I should be okay. If inductive hum is a problem some small pieces of soft iron or mu-metal should shield it out, I'd think. Maybe it's not even a concern, it's just a problem I ran into once before.

The first link is the assembly manual w/schematics for the SCA35 and the second is an article that runs down some details on the preamp section.

http://www.curcioaudio.com/SCA35%20Manual.pdf

http://www.tnt-audio.com/ampli/dynaco-sca35_e.html

Now I just have to find decent replacements for those Hershey's Kisses with hyperactive pituitaries, the foreign Mallard duck tubes. They might even be okay, they nearly top out the scale on my Dyna-Jet 606.

Any additional advice, information, guidance or questionable reflections on my parentage is appreciated. Hey, where my people come from first cousins have been getting hitched for generations and it ain't caused no problems so far, except maybe for the time when Bubba Earl escaped from the root cellar and gave them tourists heart attacks. Me, I just stay indoors and mess with lectrical gizmos. I'm working on a time-travel thingamabob right now and I've just about got it figgered out.
Bottlehead
 
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Joined: Thu May 22, 2003 3:15 pm
Location: Olympia, WA

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