If those are the original knobs, the set may not have been blonde to start with; RCA had different part numbers for the lighter knobs, described as "toasted walnut" as opposed to the "standard mahogany" ones.

I'm curious: the removable top cover, screen mask and speaker grille are solid wood on my two mahogany sets; the rest of the cabinet is veneer over laminate. Does anyone know if the blonde sets were just bleached and then a blonde stain applied to complete the lighter effect? Especially since these same solid pieces are noticeably darker than the rest of the cabinet. I did a 40-155 Philco that way once. My original intent was to remove a number of cigarette burns to the top but the bleached effect was nice and looked like just another variation of this common set so I never went back to the (darker) mahogany stain. I've toyed around with the idea of bleaching one of the 621 cabinets but don't want to do anything too drastic. If I can get a reasonable fascimile and some different knobs, I just might be tempted to try.