Hum sound

I have a valve amp with xlr input but the amp is not balanced.There is a hum when using xlr cables and i tried different xlr cables it is not the cables.When using rca no hum.What is the best way to ground the xlr connector pin 1 in amp.Can someone please give advice.
Do i need to ground pin 1 to the chassis
Not all XLR's are wired the same way.  What is the manufacturer of your amp?  Maybe check with them to see how they wired the internal XLR pins.

You could send the amp back or have a cable company wire a set of cables to the correct pinout for your amp.