There may be other +6V supplies in the rig, but the +6V Reg line feeding the VFO is only generated on the regulator board. If you're seeing +6V at the VFO it almost has to be on pin 13 of the PB1547 board. You might check that again and also check to see if the +6V supply is reaching the VFO mode select switch which is where it goes before it runs to the VFO itself. Don't get hung up in the voltages on pins 8 and 10 of the regulator board. Those feed the Clarifier (RIT) circuitry and in the PB1547 version of the regulator board they're derived from the +13.5V supply as opposed to deriving it from the +6V regulated supply as they did on the earlier 1314 version of the regulator board. It's likely that your PB1547B board does have circuit changes relative to the base PB1547 board so don't get too hung up in specific components and reverse engineer the schematic if you have to, but the +6V regulator should be similar to what's shown in the service manual for the base version of the board, a regulator IC and pass transistor that sets the +6V bus voltage. When tracking funny supply problems, it sometimes helps to break the existing supply circuit open and inject a known good lab supply. For instance you could lift the side of R12 that connects to the pass transistor and pin 1 of the regulator IC and inject a known good +6V from a lab supply with the negative lead of the lab supply connected to chassis ground. See if your receive warbles go away when you do that. It does a few things, it tells you if oscillations or ripple on the +6V supply is causing your receive distortion problems and it also validates the +6V from the regulator is actually reaching the VFO as it should. Of course putting a scope probe on pin 1 of the regulator IC may be a faster way to figure out if the +6V supply has issues.