Weird Hps Ballast..

ok i have this problem about 3 years ago i figured id give growing a try... i found a hps bulb in my buddies bastment i asked him if i could have it he said sure.. soi bought a ballast to go with the bulb i bought a 150w ballast kit from the store ... was by sylvania came with the transformer gescap and ignitor... i looked up how to wiree a ballast online and within 20min i was all set up with the bulb runing.. never had no problems..i used it for about 2 mounths then i killed my plants and put it all away.. the i began again about a mounth ago been using it.. i was talking to a buddie that grows aswell and he said he had a 150w hps bulb he wasent using anymore.. i said sure good to have a newer one since the one im using is close to its last days.. anyway i take it home i go to test it and realize this bulb is like double the size.. i put in the 150w it turns on lights up nicely then after 10min shuts down .. i cant understand why it wont work correctly.. the ballast has a label that states HPS 150w bulb type S55.. and that 150w bulb on the package says S55.. i just dont understand ..if anyone has any input or ideas on the problem please share.....

:confused:

could be the bulb if the old one works just takes a few minor dings to kill it by accident on the trip home

allright well i think i fixed the problem... talk about oops i checked most of the wiring earlier just to see maby i messed something up...dident see nething out of the ordinary.. i just ripped the power cord out of it to see maby i needed a lower guage wire.. apparantly i mixed up the com and 120v wire.. jeez lucky it hasent malfunctioned yet..its now preforming beautifully..:D thanks for stimulating my mind invision:D