S4 Leko body 575w cap vs. 750w cap

I am not aware of any difference between bodies themselves, my understanding was the only difference was in the lamp caps, today I don't think they make the '575' cap anymore, I'm pretty sure they're all 750

The original series Source 4's will not accept a newer style cap.  There is a difference.  The older ones had a slightly different back end where the cap goes on.  THey have little nubs that don't let the new caps on them.  I have plenty of these in my rental stock, so it's sort of a pain.

In addition, there are some Source 4 fixtures that were built before the 750w lamp that will take the 750w cap.  We have had a full rig of them operating on Mary Poppins for going on 4 years now with no problems that we have heard of in the shop.

I can't remember where I may have heard this now (either from official ETC info or not) but I believe you could grind the nubs off to make the new caps fit, I have not needed to test this theory yet as the need has not arisen

*edit* my statement of there not being a difference was simply on the basis of the reflector etc, I had indeed forgot about the change in the cap mount */edit*

I work at a theater where we did just that.  I took a angle grinder and cut off the nubs.  The new caps fit on nicely now.