Hi Deril
two things to consider :-
1, small transformers output can 10 or 15 % larger off load , than at maximum load
2, 12v rms when rectified will give you up to 16.9 v dc ( 12 x 1.414 ) across C11 & C12
on the diagram supplied by Les
the diagram indicates this voltage drops to 15v with the load on the power supply
this is about the minimum for the regulators to work
If I remember correcly the 1 amp regulators need an input of 2 or 3 volts more
than the expected output
I think the negative regulator will be KA7912
If you search 7812 and 7912 you will find a large number of data sheets
eg National semicondutor part start with LM , fairchild parts with uA
note – if the transformer output is too high , the regulators will run too hot without heatsinks
the metal tab on the 7812 is connected to ground but
the metal tab on the 7912 is connected to the input !
in this case the transformer does not provide mains isolation
the +12v is connected to the rectified mains from bridge rectifier B1
John Swift