[Arran]

It looks like the PENDD61 valve/tube must have failed, so someone replaced it with the EBC33, which is a double diode-triode like a 6Q7, and replaced the power output tube with whatever the other one is (can't find an EL53 is it an EL35?). Someone went through a lot of work to do this as you can use the more common 4 volt version with a dropping resistor for the heater, but maybe they figured adding a 1st audio stage would improve performance? Now if I ended up with one over here where power pentodes with detector AVC diode are non existent, the set would probably have had the 78E replaced with a 6B7 (the alternative being to add SS detector diodes somewhere), and the pentode replaced with either a 6F6/#42 or a #41/6K6 with adaptor. If the cabinet is good I would wait for a parts set with a smashed cabinet, or a parts chassis rather then completely undoing the modifications, or you could redo them to make them better copying the A537 schematic, but the chassis layout looks a little different, which was not a very Philco thing to do.
Regards
Arran