Power supply regulatable
0-28V 20Amp By LM317 and 2N3055

Part list for 20 Ampere regulatable power supply:

• 2 x 15 volt 20+- amps

• D1...D4= Bridge rectifier MB2504 (25 amps cooled)
  or eight BYW29 8 amp diodes (TO220 pinning cooled)
  or 8 x MR750 (MR7510) diodes (MR750 = 6 Ampere diode) or 16 x 1N5401 (1N5408) diodes.

• F1 = 2 Amp

• F2 = 25 amp

• R1 2k2 2,5 Watt

• R2 240 ohm

• R3,R4,R5,R6 0.1 ohm 10 watt

• R7 6k8

• R8 10k

• R9 47 Ohm 1 watt

• S2 mini switch

• R10 8k2

• C1,C7,C9 47nF

• C2 four times 4700uF/50v or one 22000uF/50v

• C3,C5 10uF/50v

• C4,C6,C9 100nF

• C8 330uF/50v

• C10 1uF/16v

• D5 1N4151

• D6 1N5401

• D10 MR750

• D11 LED

• D7, D8, D9 1N4001

• IC1 LM317

• Two 2N3055 transistors

• P1 5k

• P3 10k trimmer

• relay = 30 volts AC, 2x10 amp switching

S2 switches between +- 3 Amps and full output current

The relay is used to switch off the power supply voltage when the mains (S1) are/is switched off. So no delay do to the discharge of C2, and so preventing output voltages from not return to zero immediately.

A MB2504 is used as it is a 25 ampere rectifier bridge which also should be cooled. Or you could use eight BYW29 8 amp diodes (TO220 pinning) mounted on a heat sink.

Mount a little heatsink on the LM317 IC

Remember to isolate the 2N3055 transistors from the chassis/radiator! Use a radiator (heat sink) of appropriate size and surface area; insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste.

Read More Source :
http://users.belgacom.net/hamradio/schemas/
6-20amps_regulatable_powersupplies_on6mu.htm
Thank you.