F1X hum problem

[bumhucker]

I just bought a used F1x and I love it very much but I'm having a hum issue.  The DI out hums.  The ground lift switch has no effect.  If I have the full range out and the DI plugged into the same mixer then the hum is gone.  The Full Range out by itself sounds amazing.  I tried cables, power sources etc.  I cleaned the FX. Return jack, exercised the jacks., tried different tubes.  Anyone have any ideas?  I searched this forum and read up.  I am going to have a tech check it out but the insight on this forum is always top notch and would the tech at the very least.  Thanks!!

[hammer]

Have you checked this post and Edwin's advice.  http://club.alembic.com/index.php?topic=22256.0

[bumhucker]

Thanks--I'll have them checked!  That actually may be related to another thing I noticed.

[edwin]

I don't think it's filter caps if there is a way which you can hook it up without hum. Old filter caps create global hum. This sounds like a bigger problem between stage power and the FOH or perhaps a bad mic cable. As an interim fix, you could always run a DI off the full range out between the preamp and the amp. If you still get hum, then you know that it's not you.

[bumhucker]

Thanks--I did try it through two different mixers in different locations with different cables and power still have issues.  I also tested my GK head's DI and it was fine in the same situation.  I appreciate the info-this will help me and the tech narrow it down.

[bumhucker]

Just for posterity-
I finally found that the xlr jack ground tab (the 4th connection on the jack) was not actually grounding to the chassis!  I noticed that it was a Switchcraft so maybe it was a replacement?  I put a Neutrik in there and it seems to have solved it!!  There was no metal to metal contact on the old one. I realize I could have just scraped the inside of the screw hole on the jack but I figured a nice jack can't hurt....

Thanks again!