Hello. I need help changing a 24vdc 6a power supply to a 5vdc 40ma to operate a 555 chip. any suggestions

 

It would probably be easier and lots cheaper to just get a 7 - 9 volt DC wall transformer and a 78L05 voltage regulator.

 

I certainly agree with beenthere:

However if you have the 24V supply at hand and are resolved to use it, you could build a small LM7805 regulator circuit:-

http://cva.stanford.edu/classes/cs99s/datasheets/LM340.pdf

As long as you keep the LM555 load circuit current to a conservative value say ~70mA max, you could probably get away with a TO-220 package without any heat sink (assuming a maximum ambient temperature of (say) 40 C and R thermal(J-A)=55 C/W ).

If you are confident with electronics construction you make it something like this ..

http://peterflemming.ca/flemmweb_current/schem/opamp_linear/7805.pdf