[Chas]

What am i missing?

   

The lead wire on the left  

This cap will affect the high frequency audio as well as clip spikes from static. It will also aid in the reduction of "tweet", that is the high pitched whistle from an adjacent carrier. Indirectly, the cap will save the output transformer...

The "mod" may have been at request of the user for any/all of those reasons.

Use the schemas 110pf, see how it sounds, if harsh a 330,470 or 510 will suffice, it is not critical. Use a silvered mica as a mush-a-lized yellow cap doesn't come in that small a value

If your a stickler for authenticity I may have all those values in NOS mica, Aero, Cornell, Elmenco.

Fair warning, can't get so cavalier with mica's in the RF section, no mica twisting as that will cause another handicapped cap Buy that cheap plastic dental mirror to look around corners...

Chas