Source 4 Par EA 575w or 750w

As I understand it, Yes is the answer to your question.  When the fixtures first came out, there was only the 575 version.  With the introduction of the 750 watt lamp, they were all upgraded to be the 750 watt version. This upgraded the wire inside to rate it for the 750 watts as well as a couple of other small items. 

The other thing is that maybe your 750 watt stickers have just fallen off the back of the lamp cap?  :-)

This is my understanding, but Im not absolutley for sure about what all was done to the fixture during the upgrade.  You will really have to ask Tom Littrell for the whole truth.

Thanks Jeff,

I think you answered my next question, what is the diffrence between the two versions.

Henry

Another change was the integral safety attachment point included on all newer fixtures.

To answer Henry's question.

The quickest way to identify what rating your source 4 cap is look where the lamp plugs in.  There were 3 major revisions to all fixture caps.  If you look where the lamp plugs in you will find 1 of 3 styles, this will tell you the rating of your cap. 

1 - There are no key holes below the contacts for the lamp - Rated for 575w

2 - There is 1 key hole below the contacts for the lamp - Rated for 575w, and 575w 77v (dimmer doubling)

3 - There are two key holes below the contacts for the lamp - Rated for 575w, 750w and 575w/750 77v (dimmer doubling)

See S4 Cap.doc attached to this post for pic

P-