[Ron Ramirez]

It looks like the type 6 ballast tube socket was there, I can see that the rivets were ground out. If I am understanding things, a 38 would have had the socket, but a jumper would have been placed across the filament contacts. Does that sound right?

That is correct. I've owned a few model 38 sets over the years; all of them had the socket for the #6 ballast, but all had a removable heavy jumper wire across the filament pins of that socket. The stickers on the back of the chassis indicated "CHASSIS TYPE 38" and not "38A".