[Radioroslyn]

The two that are fixed to the chassis are Philco issue. The third can isn't and just has two leads, a red & black. These equal the + and - connections. There is no connection to the outside part of the can. On the Philco parts there is a connection to the can.
The - connection on the Philco caps is done thru the metal clip that is fitted between it and the cardboard insulator. B- is not at chassis ground as use to provide - 15v or so to the control grids of the 42 tubes. That's also why that 10uf cap looks like it's in backwards. It's filtering - voltage or the - side of the power supply. We can dig into that later if you like.
 
What looks confusing is on 77 is one of the center terminals is connected HV and the terminal right next to it is connected to chassis ground. You rarely see any of the center connections connected to chassis ground. Typically electrolytic cap in a can the - are all connected to the outside shell.
All of the + are terminated at the bottom and have makings to tell which is which. There just about all the time they are at a + voltage. Back to the 3650 the outside of the can (shell) would be at -25vdc or so both 77 & 78 caps.