Okay, looking at this schematic: http://ucapps.de/mbhp/mbhp_sid_c64_psu.pdf
Is this going to be adequate voltage for the 6851 or is this only for the lower voltage varieties?
Is this going to be adequate voltage for the 6851?
Yes.
And you transormed it with a Voltage Regulator:
7809 for a 6582 or 8580
or
7812 for a 6581
Yes, well I have the 7812 on my SID board and I assume that’s adequate enough! Looks like it’s working, but I haven’t checked after my 7812 yet as I’m still in the assembly phase. But I will most definitely be checking before plugging in my SIDs.