[Arran]

Without looking at the schematic it sounds similar to what many table sets and small consoles used in the early 1930s, they took the output from the second detector tube. I found the schematic on Nostalgia air, and it shows that there is a 25 K resistor between the full B+ line and the primary of that interstage transformer, so I think maybe the voltage spec was in error.
Assuming that the rest of what they quote for the second detector is true then the plate draws a current of 8 ma, so if there is a 25K resistor in there then it would have to drop 200 volts, therefore the plate voltage for that 27 should be 75 volts not 255 volts. See if there actually is a 25 k resistor in there and not a 2500 ohm one or something, either the 255 volt measurement is wrong, the current rating is wrong, or the value given for that resistor is wrong. As my math teacher used to say, "Ask yourself the question, does this answer make sense?".
Regards
Arran