[Arran]

I have always heard of them refered to as Philco Hex knobs or dome knobs not acorn knobs. When someone mentions acorn knobs I usually think of the bullet shaped knobs that came about in the late 1930s on Philco and other brand sets that are flat on the back and pointed toward the front. The station selector knob is probably the largest of the three styles, over 1'' in diameter, and there would only be one of that size used on any given set, there would likely be two of the other sized knobs to be used, probably two of the larger kind and the smaller one between the two larger ones.
Regards
Arran