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In Reply to: Dynakitparts SCA-35 posted by petercapo on November 8, 2014 at 12:27:01:
Years, actually decades ago when I had my Dynaco collection, I had both a nib factory built and kit versions of the SCA35. I had the factory one checked by a tech who tested and confirmed it easily met and exceeded the published specs. Sound wise it was quite decent. I preferred it to my bone stock ST70 and PAS3x combo.
I took the kit and decided to strip the boards and while using the unit upgrade items like the controls and I also built discrete circuits of each PEC. I subbed in metal film 1-5% resistors, each 1 higher wattage rating than the original and new and better caps. In the past I increased the filter caps but not by much. I replaced the original bass, treble and volume controls with new more closely matched ganged controls. The tone controls were individually tested until I found ones that at the null point, both gangs were at about +- .1 db. The originals though in theory were supposed to null were so far off they did not. Same with the volume control where I used a ganged but separated inner and outer shafts, eliminating the need for the balance control which I bypassed. I do hate balance controls.
The selector switch was left stock, at the time I could not find a decent replacement. All wiring was mylar coated silverplated either single strand or multi. From the jack set to the selector all wires were shielded and run through a copper flexitube. The power transformer was encased in what I called a poor man's Faraday case. The jacket was replaced with better jacks, not gold as at the time these were not in vogue. The loudness contour circuit was eliminated as I never use it.
The tone controls were checked through a scope and the null points were marked on the faceplate.
The amp was checked by the same tech who did the factory unit using the same equipment and tests. The resulting specs were far better. Both units had the original nib tubeset. We then tested them on an agreed to set of speakers, My back then fairly new W70D Wharfedales. We used the same input source, a Crown HS 2-track deck and Garrard 301, can not remember the arm or cartridge.
After a number of good between the amp's using a patch cord switcher but no blind testing we both decided the kit as updated clearly sounded very noticeably better. It was the tech who laid the seeds of the idea of using a separate chassis for the power supply but, I never got to it. As it was, this SCA was the last tube amp I kept long after disposing of all my tube units around 2000. I finally sold it a couple of years ago. I had a couple of thousand hours on it and the original tubes were still huffing and puffing away nicely.
I think the biggest failings of the Dynaco products their choice of components. They invested in the opts and circuit design but then cut the corners everywhere else to meet their targeted pricepoint. Sadly, this seemed to be David's failing in all his products throughout his career.
Don Brian Levy, J.D.
Toronto ON Canada
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Follow Ups
- RE: Dynakitparts SCA-35 - Brian Levy 07:03:16 11/13/14 (1)
- RE: Dynakitparts SCA-35 - petercapo 07:15:42 11/13/14 (0)
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