Wurlitzer 200A +15V supply question

[David68]

I'm working on a 200A with its original amp, and the +15V supply is a bit on the low side at around 14.2V. I realize that this is not a precision device, but I was wondering if anyone knew exactly what provides the voltage reference for the regulator chip since I don't know what the circuit is inside the chip. Will the 15V supply be off if R54 and R55 (10k 1%) have drifted?