MusicMan 2475-130 design error?

[vintasonic]

Got a 2475-130 on my bench, the model with the 12AX7 PI. The schematic shows - and the amp is wired as such - that all the cathodes are tied together (on the schematic shown as 'y') and there is a 10 ohm resistor at either end, both tied to ground, making it 5 ohms to ground .  There is a service bulletin that has a note on biasing and talks about only one resistor.

Not my first Musicman nor my first tube amp, I've repaired hundreds, so I post this because it strikes me as so odd.  Breaking the cathode link between the pairs of output tubes would seem to be correct, that way you could measure bias of each pair.

Any one have any insight? Again, this in the schematic and looks like factory wiring. Here is the schematic https://www.thetubestore.com/lib/thetubestore/schematics/MusicMan/Musicman-2475-130-2275-130-Schematic.pdf

[sluckey]

Breaking the cathode link between the pairs of output tubes would seem to be correct, that way you could measure bias of each pair.

You could do that. If I owned the amp I'd probably just use four 1Ω resistors, one for each tube. If it belonged to a customer, I'd let it be. There's nothing wrong with the way it is. The note on the schematic says adjust the bias for exactly .5V at point Y. So, .5V/5Ω = 100mA. That's 25mA/tube (assuming perfectly matched). Easy math. Sounds reasonable.