The original X-101ST is a good example regarding knobs Fisher used in the very late 50s. The original unit had the knobs of 400C preamp of discussion that just sold. It was then updated with newer (less architect looking) lighter brown colored knobs, but still with no individual channel adjust. The final version of the same amplifier used the same style knobs, but then incorporated the ability to adjust each channel individually. I'm relatively certain that all of the Fisher equipment that was available during this earliest period of stereo went through this same transition, which by all appearances happened fairly quickly -- and it may be that it was only with the X-101 ST and the 400C, as they are to my knowledge, the earliest non-receiver/tuner stereo pieces offered by Fisher.
Dave