Fender princeton humming

I have a 1972 Fender Princeton reverb amplifier, it has a humming sound. I have replaced the cord and checked the ground, it still hums. Any ideas?

Well It Can Be Several Things Like
In a Room Where It Has Flouresent Lighting
Or Shareing a Plug In The House That May
Be Connected To Either The Refriderator Or Well Pump / Washer / Dryer / Computer Monitors Or
Optical Mouse's Or Perhaps Your Guitar Isnt Properly Shielded or It May Need a Tube Change

Thing Is You Need To
Try Things Out In Differnt Parts Of The House And
Dare I Say Times Too Because It Wont Go Away
If you Cant Isolate the Problem Haveing Checked It At your Friends Places just Might Be Worty Too
And Maybe try Their Guitars With It And See If it Gos Away If It Works With a Good Guitar
Its Possably A Guitar Shielding Problem

Good luck

I have tried this amplifier in several different houses, same thing, tried it without my guitar plugged in same thing, my guitar is a 1970 ES-335 I dont think that is contributing to the problem, I just dont know what is, where can I take the tubes to be tested?

Thanks

Someplace Like Guitar Center Should Have a Full Tech Staff Every Once In a Great While
Cap's Can Be a Problem But Im Gonna Say Its The Tubes

Thanks, I will give that a try.