The reason we do not support the "MK" series of old Dyna amps is partially economic, partially engineering, and partially mechanical layout.
Economic: nowhere nearly as many available as with the St-70 so the "pool" of possible clients is much less, likely too few to make careful engineering efforts and new board designs cost effective for us.
Mechanical: These units all have very small PC cards and there is simply not enough real estate available for new circuit designs using our design ideas that work very well, such as multiple isolated regulated power supplies. Even the Dyna St-70 required a new board that "overlapped" the size of the original by a considerable margin, no room for that on those other models.
Engineering: The power bandwidth of the output transformers of the MKIII and MKII just won't support full power flat response in the audio range, too inductive at high frequencies, too small at low frequencies, so new circuits won't cure the worst case problem - - - the output transformers. In addition the high voltage parts needed are scarce and very expensive, not good candidates.
Regarding the SCA-35, a really bad starting place. The output tubes run at egg cooking temps, the preamp section is a joke (inadequate open loop gain with single triodes for each section), the passive tone control network would be better named a distortion generator network, the high level of circuit hum is simply masked by injecting raw hum directly into the outputs out of phase. Its only virtue is that the midrange is not awful sounding, and the very limited bandwidth masks lots of other nasties. It was adequate in its day nearly 50 years ago, but no way is it a high fidelity product by today's standards. Trying to redesign that unit from the ground up would cost much more than simply buying our already available separates, and the power rating would still be tiny.
Finally, we are not "modifying" equipment in the sense of taking out the bad sounding parts and putting in good sounding parts and wires as seems to be the norm. Each old Dyna and Hafler unit that we do support is gutted and the audio design is simply replaced with ours from the ground up, essentially all new designs in your old box. Hardly a modification.
Frank Van Alstine
P.S. Our message is NOT that we are unable to fit a preamp and amp in the same chassis. Of course we can do that! The issue is whether it can be done cost effectively and supply a unit up to our musical and engineering standards with adequate power at a rational price. No point in it if you cannot afford it.
