A testament to the quality of Dynaco's original circuits is that their products were made using low tolerance, inexpensive parts (with the exception of the transformers, of course) and they were often built by complete amateurs (most people don't know that "Factory Assembled" units were built by starving Drexel University students) yet they still sounded quite respectable.
But these designs had their weak points, too. Since they were intended to be built as kits, they often made compromises in the grounding and power distribution in order to make assembly easier. From personal experience, I can tell you that one can greatly improve the sound of a stock Stereo 70 by simply changing the way the cathodes of the output tubes are grounded and by changing the reference ground points for the feedback circuit.
But these designs had their weak points, too. Since they were intended to be built as kits, they often made compromises in the grounding and power distribution in order to make assembly easier. From personal experience, I can tell you that one can greatly improve the sound of a stock Stereo 70 by simply changing the way the cathodes of the output tubes are grounded and by changing the reference ground points for the feedback circuit.