Actually, the best clue you can provide is whether it is 60 or 120Hz. Each comes from a different source for hte most part.
1. Just because you replaced the filter caps a while back, doesn't mean one didn't fail, or the solder that connects it failed.
2. Bypass caps will not introduce hum, they will affect frequncy response and gain.
3. Isolate the problem. Is the hum present without signal? Is it present with all the controls set at zero? DO any of the contros affect the amount or tone of the hum?
4. Have you recently replaced the phase splitter tube? If so is it a Sovtek?
5. You might have replaced all the B+ filters, but did you replace the bias supply caps as well?
6. Are all the jacks tight and making good contact?
7. ANy loose nuts on the pots?
8. Any loose hardware on the transformers?