[RodB]

Okey dokey, let's get on the wayback machine. Back when radios were running on batteries, they were powered by three DC batteries, A, B, and C. The A is for filament/heater voltage, B is high voltage (typically 22.5 -90 volts) and C is for grid bias. Your radio tubes get these voltages from the power transformer secondary windings. The A voltage is supplied by the 6.3 volt secondary, the high voltage secondary provides the B voltage and C voltage. It is converted to DC by the full wave rectifier tube and filter circuit.

If you look at the 7Y4 in your schematic you'll see the cathode is connected to a choke coil and an electrolytic capacitor. The other side of the choke is a second electrolytic capacitor. This point in the circuit is 180 volts and is your B+ voltage. You can follow this connection up to the output transformer and also to the left to the 220k plate load resistor. Now you can see how B+ is distributed to the plates of the amplifier tubes.