Help understanding 1986 schematic for Rohde & Schwarz cryptographic key generator
This doesn't look like a noise generating circuit.

According to the BOM on page 29, D21 to D24 are SN75150AP, so RS-232 line drivers, which need a dual +-12V supply. That's exactly what V1 and V2 are doing: being rough, regulated power supply. I'm not sure, but V3 and V4 being BZX79-C13 have a ~ 13V Zener voltage – these might simply be protection diodes.

Generally, your PDF is the manual and service manual to the V.24 serial interface card, not to the board that generates the randomness.