With a 12.6-0-12.6 @ 2A Radio-Shack piece there are a few possibilities.

One is a Full wave rectifier( CT is the negative of the supply ), and filter: Capacitor-Resistor-Capacitor. Simple and fairly easy.

Second is use a single cap, and an LM317 regulator. Slightly more complex, but voltage regulated and not disturbed byvarious 5687 filaments.

Third is to use a full bridge and an L-C-R-C. This is a bit more expensive and should probablybe done later....

The first is probably the best, keep in mind that we'll be running the 5687 at 12.6 so as to cut the current in half as compared to the 6.3-volt's requirement of an amp or so.

Resistors are not too bad, 2Watt, 1-Ohm are going to drop a half volt each( or so...) and are cheap and easy to get.

1N5407 diodes are 1kV/5A rated and have been pretty indestructable in my projects.
regards,
Douglas

....damned Thrintun!