[morzh]

Well....I doubt you will see the difference.
This said, it is not really part of the filter.
Were it part of a filter, I'd say, no difference; this one, however, is to compensate the residual ripple after the inductance. As you know, capacitor shifts the current -90 degrees vs voltage, whereas inductance does the opposite, so the two of them create two ripples 180 degrees apart, and if sized right, the cap could cancel out the residual ripple.
Philco calculated that value to be 0.13uF.

Now, many of us simply do not even populate this cap, as we found out it is not effective at all, and simply beefing up tthe second filter cap (lugs ## 1&4) could have much better effect on the ripple and thus on the hum.
I think at the time they simply did not have good caps, so the second cap (not the 1st one) could be increased quite a bit. A 20uF cap is not out of the question.