[MrFixr55]

If memory serves me correctly, tolerance for old school 'lytics were something like +80 / -20%, so the cap could be 20% low or almost double the rated capacity.

I don't know why capacity of filters was so low back in the day. Go forward a few years and instead of 8 or 16uF caps, you see more like 20, 33, 47uF and still saw a field coil doubling as a choke. Did cap tech improve, causing manufacturers to raise capacity of what was installed?

Granted, if increasing capacity, this may raise B+ but may improve hum. However, if it works well with the originals, then leaving well enough alone would be a good idea.

80 / 5Y3 are rated for up to 40uF cap from cathode to center tap, but that may be for later versions; that spec is not in the RC10 (1932?) version of the RCA Receiving Tube Manual but is in the RC14 (1940) version of the manual. This may be because by then, the 5Y3 had come out and the 80 and 5Y3 have the same specs but with the 5Y3s improved filament