Question:Transformer for Bi-polar PSU

[rufustf]

I'm all set to build the Bi-polar PSU as shown on ggg, for 9V. It says to use a transformer that puts out 12V. What I have is a transformer that puts out 24V. I noticed that in the anderton sch. it uses a 24V center tapped trans. going into + & - 8V regulators. If that works, I'm thinkin I can go ahead with the trans. I have (24V, not center tapped). My caps are rated at 25V. Should this work or should I go ahead and get a 12V trans. as stated in the instructions? Thanks in advance.
Jason Myers

[Paul Perry (Frostwave)]

If you have a 24V transformer, and it is not centre tapped, then sorry, you are out of luck for making a 9v supply.
Because, one side of the transformer has to go to ground & the other to a pair of 1/2 wave rectifiers (one +, one -) and at 24v AC input, you get a peak input to the regulator of 1.4 x 24 which is 33V or so, not what you want to run into your 9v reg, even if it handles it as input, the voltage drop across the regulator means you cant hget much current thru without overheating it. (power dissipated = votltage drop x current draw).

Most regs are 35v peak input, too close for safety.

[puretube]

if you happen to have an "open" transformer, and if it happens to have a CT or 2coil primary which allows 110V or 220V operation,
and you happen to live in a place with 110V mains voltage,
you could wire the primary for 220V operation, hook it to the 110V mains,
and voila: it puts out 12V instead of 24V...

[rufustf]

Hmmm,...
I got a 12.6V trans, built it, and the meter reads a bit over 9V when connected to the + & - output. Now after about 5 min. of being turned on, the - regulator heat sink it pretty hot, while the + regulator is only a bit warm. The guy at Electronics city may have given me the wrong regulator, (it doen't say 7909 anywhere on it), or I made an error with the transformer, which says 6.3 V on both secondaries.

Also, it doesn't seem to provide power to a working effect that I'm sure I wired correctly, as the 2 batteries still power it when the cable from the
PSU is disconnected. I used 1/8 stereo plugs with a 2n.c. stereo jack in the effect. Wired incorrectly there's no way the batteries could still provide power.

The meter reads 9V+ at the reg. output, and nothing at the 9V- reg. output. I suspect the 9V- reg. but I'd really dig a 2nd opinion on the subject as this is my first project dealing with AC wall power.

Again, thanks in advance,
Jason Myers

[puretube]

neg. regulators love to have a different pin-out than the pos.regulators...
:?:

[rufustf]

Right, looking at it from the front with the pins down, it's out, in, ground from left to right, correct? That's how I have it wired. The heating imbalance is what has me worried, or is it supposed to get that hot? That neg. reg. really starts to cook after a very short time, plus it doesn't do it's job.
I'm going to see if there's any difference in the pin layout for different manufacturers of the -reg. If it's working, the meter ought to read 9V when the - probe is touching the output and the + is grounded, though I tried it the opposite way too and the -reg. doesn't read any signal at all.
Thanks for the help.
Jason