PSU +/- 18 Vcc and -24 rail

[Aleguitarpro]

Hi.
I need to build a PSU for 2 SSL 502 EQ modules.
I've several 15-0-15 transformers and I think it's enough to have a dual 18Vcc rails (15x1,41= 21,15 for rail so enough for a 78/79-18 regulators).
So, the dual rail with a 7818 and a 7918 it'is not a problem.
I think to get the -24Vcc with a doubler and a LM337.
Please, could someone check this schematic because I've all the correct voltage but after a few seconds the positive 18 rails starts to lowering his voltage and C3 and C4 became very very warm...

I haven't found any reference about the use of a doubler with a negative rail but maybe there's an error in the use of the positive rail of the doubler as ground.
Thanks for help.
A.

 

[Matador]

Aren't C3 and C4 backwards?  The + side should be towards the higher "DC" potential.

EDIT: stated another way:  With the "top" of the bridge at ground, the bridge connections (where the caps couple to) will only turn on when the rail goes below ground.  The the signal will swing between one diode drop above ground and the negative going peak of the cap-coupled supply.  This means that for a 18V transformer secondary, those nodes sit at an average value of -10V or so.  Reverse biasing the caps will convert them to near short circuits, which may be why it drags the positive supply down.

 

[PRR]

> C3 and C4 became very very warm...

What Matador said. Probably.

If you are un-sure, put voltmeter across the warm cap, noting which is red or black, + or - on cap, and what +/- the meter shows.

Wear eye protection! And don't do this on the dining room table. A warm cap can get hotter and burst. A little 680uFd 50V is not a big BOOM, but it will splatter borax and shredded paper ALL over the room (and in your face).

 

[Aleguitarpro]

Thank you very much!
I've tried today and reversing the two caps all it's ok!