Finding the correct capacitor for a 433MHz RF with HT12D
lets suppose you need 0.1 amps to run the radio.

lets suppose you indeed have implememted a successful full-wave rectifier, which produces 2 * 60 Hertz output ripple of 120 half-sinusoids every seconds. We need to store that energy.

Suppose 1 volt ripple is tolerated by the regulator.

Let us suppose the transformer is good, the core is good, and the transformer produces 12 volts * sqrt(2) or about 17 volts peak.

The regulator may or may not be happy with 17 volts peak,including OVERHEATING, or not surviving the 17 volts.

But lets soldier on.

Using Q = C * V, taking the derivative, and assuming dC/dT is ZERO, we end up with

I = C * dV/dT, and rearrange that to have the very useful

I * dT/dV = C

Sticking in numbers, we have

0.1 amp * 1/120 second / 1volt = C

0.1 * 1/120 = C

0.000833 = C ==== 833 uF should suffice.

But if that has failed, then 


the wiring is wrong
the regulator is broken
the transformer/rectifiers are bad