[tab10672]

17y (.03) goes to the tone control switch. Just because the other cap goes to the 5Z4, the schematic may not show a direct point A to B link. The 5Z4 pin may have been the closest B- (or whatever) to tie into. But if you trace that cap from all the connections you will find a lead somewhere on the scematic that will tie them together as it is in the radio. Also sometimes when a tube doesnt use all the pins then the unused lug at the tube socket may be used as a junction terminal.