[Robert Gribnau]

With V+ disconnected the screengrid volatge of B4 is 'zero'/floating. Under these circumstances B4 should hardly be passing anode current because in pentodes the anode current depends largely on the screen grid voltage (and control grid voltage) but hardly on the anode voltage.

What happens when you remove B4 with V++ still connected to S23 and V+ still disconnected? Does the rectifer than still struggle? How do you know it struggles? Rectifiers and power valves get hot even when working normaly. Can you measure the current between the rectifier and C1?

Addition: If there really was no connection between the anode of B4 and S23 than I do not see how you would be able to still hear some stations.