Just for the record, that circuit and board layout are counter-intuitive. While one is tempted to think they are a mirror image layout, they aren't.
The diode D5 is the reference for the 65v to 49v regulator.
the -49v regulator is a mirror tracking regulator, which tries to keep the base of Q14 at -0.6v, with the R38(47k) / R39(47k) + R40 (120 ohms) voltage divider
connected to the +49v dc and -49v dc rails.
R37 is the limiting resistor paired with the C32 / D6 24v zener making QUIET and clean 24v dc for the phono / eq amp's input stage.
THEN the bean counters changed D6 to a 5100 ohm resistor, although with the low draw of 120k resistors, the voltage divider scheme gets ~ 25.5v and MAY be quieter than the zener diode.