Help with tonepad`s power supply

[jn777]

Hi i recently build the power supply posted on Tonepad http://tonepad.com/project.asp?id=59 

ive changed this components due to availability:

Diodes(6): 1n4004 instead of 1n4002
Resistor: 220ohm instead of 240ohm (for the regulator side).

Used a 12v 500mA central tapped transformer, which i connected 2 outs the circuit and central tap 0v as ground.

The maximum amount of voltage out i get is 6.03V with the trimpot all the way to the maximum, and the minimum voltage is 5.42V
Also the diodes that receive the 12V and ground from the transformer get really hot, and they start to smoke, maybe the soldering paste that was left, but also i can notice that the board looks a little brown 

What could be wrong?
does that resistance value change, be the one making this power supply not reach 9v?

Thanks in advance!

[Ice-9]

it sounds like you have the transformer wired wrong. what are the windinig labelled as. eg. 6'0'6 or 12'0 etc as i dont think you should have the centre tap on the secondary side to ground. Sorry really fast post as i'm about to leave work.

[jn777]

There is only one side labeled, the one that is not labeled has only two wires(black).
The labeled side says:  12V  500mA,  and 3 cables come from this side 2 browns(1 on each side) and one white with a red line(this one comes from the center)  I took the white with red line as center tap.

Thanks a lot for your time!

[jn777]

Got it fixed thanks to Ice-9,  i took the Center Tap out of the board, and now i can get 9v out of it, the diodes do not get hot!
Now im going to wire everything to test it.

[Ice-9]

Glad you have got it working, the diodes shouldn't get hot though, maybe a bit warm to touch. The use of 1n4004 instead of the 4001's is fine, i believe they are rated at a higher voltage if i remember correctly. The resistor you replaced (240ohm) and the trim pot is what is used to calculate the Vout.

Here is some info on how the LM317 voltage regulator works, it gives some insight on how to calulate the Vout using maths for the resistors if your interested in how your new psu works.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#317.gif

[jn777]

Thanks a lot Ice-9, now the diodes do not get hot, before i did what you told me it was really really hot, to the point it started to make some smoke.
It seems that when i used the central tap the voltage is divided to 6v-0v-6v thus providing less Volts to the regulator.
Now with the Central tap out of the circuit i get the full 12v.
I was able to regulate it to 9.1V steady.   

[Ice-9]

Hi, The reason it wouldn't work with the center tap to ground, is that the output from the secondary windings from the transformer would effectively be shorted out to ground through the diodes in th ebridge rectifier. Hence the heat and smoke.

Congrats on getting it all working .