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In Reply to: RE: The Dynaco SCA-35 is back! posted by mark.korda@myfairpoint.net on April 13, 2014 at 11:35:38
Nice! However, I don't have $1K burning a whole in my pocket. I do have a working, all original (except for the diodes) factory assembled SCA-35 that I paid $35 for quite a while ago. I still can't decide what to do with in. There are not too many virgins left! Fare more interesting to me are the available parts that this company is also supplying.
Dave
Follow Ups:
Hi guys,I haven't yet passed my Heathkit DC electronics course yet even though it's been sitting on my wire rope spindle coffie table for over 20 years. So I'm always looking for answers,and I appreciate all your help,I mean it. But I must quote someone and you guys can debate it because your way smarter than I. I asked this question on another site 3 years ago. What do the hum controls on the back of the Dyna SCA-35 really do? I thought they set the power tube bias,I didn't know. Frank VanAlStine gave me this answer: The hum control simply interjects power supply hum into the output,out of phase with the output hum,a kind of 2 hums are better than 1 scheme. The circuit conditions that cause the hum are still there, just masked. Not a good engineering solution. Also in his Audio Basics newsletter,free on his site, I subscribed back then, he explained the plight of the 7199 tube,being noisy and rare and such and he used the word (unobtainium). I don't know who coined it,and I don't care but it's dated and inwriting. I'm not trying to be stir up the nest, I just wanted to share some facts I learned 3 years ago and in 1982 (Audio Basics). Thanks I love you guys but had to get that out of my system.....Mark Korda
I don't think it is all that controversial. I think there are few here who would doubt Frank VanAlStine's technical qualification or knowledge of Dynaco. I have one of his early Super Pass modification of a Dynaco PAS preamp, and it is very well thought out and executed.
By introducing the hum out of phase, they cancel each other out. It would be better to have a hum free circuit, but canceling it out is better than nothing.
7199's are rare and expensive. It is a fact for a lot of tube types. You can substitute a 6GH8A with a rewire or adapter, but they are getting harder to find too. There are also new boards that change the circuit to and ST35 type, but use more available tubes.
Dave
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