My little kay 507 tube amp hums like crazy.  How do I fix this?

sounds like your filter caps have gone bad.  replace them...
but : WATCHOUT, THE CAPS CAN HOLD A CHARGE AND IF YOU
DONT KNOW WHAT YOU'RE DOING, IT'LL KILL YOU.

If this makes you nervous, than i would get a qualified amp tech
to do it, or study up on how to discharge caps.  remember,
if you work on a tube amp, only use one hand, and keep the other
in your back pocket.  if you have one hand on the capacitor,
and the other on the chassis, the current could go through your
heart and you could be pushing up daisies.......

ok, though a little OT, here we start:

1.) How old is the amp, since when do you have it, and when did it start humming?

2.) Does it smell unusual, when on?

Well you could have bad tubes, bad caps, a bad ground connection inside, a bad part somewhere. Its kind of hard to give a good diagnoses without more information. Saying "I have a hum whats the problem ? is like going to the doctor and saying "I don't feel good what wrong ?"

Check out the tube amp FAQ. If you haven't worked with tube amps or high voltage you might was to just send the amp to a good tech.

Andrew

QuoteMy little kay 507 tube amp hums like crazy. How do I fix this?

Read the tube amp information at http://www.geofex.com.

In particular, the Tube Amp Debugging Page, and after that the Tube Amp FAQ.

99% of what you need to know is in those files.

Yes, check out R.G.'s document. It's really good and it has helped me a lot.

I've changed the power supply caps on different amps with success!

Thanks R.G.!

You could possibly have a bad connection to ground. Maybe a wire to ground has worked loose or something. This could be especially true if the connection to ground relies on a wire that is screwed to the chassis or something.

The usual other things are bad tubes or bad filter cap(s).