Ripple Rejection DC power supply

[kumar_prashu]

Hello
I m trying to make a variable voltage Rectified power supply using LM338. But i am facing an unusual problem of ripple at the output of LM338. when I set the Output at the particular voltage, the ripple current at the output just doubles the DC value.
just as if DC o/p = 12 volts.
AC o/p = 24 volts.

The exact specs. of the components are as follows:

Transformer- 220/15-0-15 volts, 5 Amps. (center tapped)
Diodes- MIC 6A4
Cap.- 10,000 microfarad /25 volts.(at the o/p of rectifier)
large value is just to keep the low ripple

LM338: 0-5 Amps. input- output differential voltage = 3 volts

Why do this happens.
pls explain.

I want to completely remove the ripple content.

[MP]

How are you rectifying this voltage? Post a schematic.

MP