Hello, I'm troubleshooting an R-4B and am searching a later SN schematic, which has OB2 regulator voltage included (V11) and a PCB board not included in the first models. So far, I've had no luck yet, but found and downloaded only two different copies but are for low SN rcvrs. Any scan or pdf would be helpful. Thanks in advance Regards Guillermo - LU8EYW.