Hum is common, but not a requirement of using tubes. It often takes some work, but you might be able to reduce the hum more. But the first thing you have to do is see if the hum is originating in your tube amp, like Mike suggested. If it is, then to reduce hum you need to mod or replace that amp. A shorting plug is simply an RCA phono plug whose positive and negative terminals are connected together, aka the signal (+) is shorted to ground (-.) You can make one with an old plastic midfi interconnect, as long as it fits tight and is clean. Cut off an RCA plug along with 4" of cable. Strip the ends of the cable 1/2" and twist or solder them together. You'll need two of these plugs to short the L and R inputs simultaneously. If it is integrated amp, set the input selector to the input that has the shorting plugs installed. This will make the amp as quiet as possible. Only the power cord and speaker cords are connected, no ICs connected at all as they can cause hum even if not selected. You could also try lifting the safety ground of the tube amp temporarily, using a ground buster adapter. This is for diagnostic only, to determine if your house circuit wiring might need some connections tightened. You must not run the amp without safety ground, no matter how good it sounds. Tube amps have high voltage DC inside, so you really need the safety ground to protect your life.
Hum is most often caused by either high impedance grounds (which should be low impedance grounds) or EMI.
A ground connection must be low resistance to work right. Resistance causes current to flow which is the cause of ground loop hum. Where there is supposed to be low resistance ground connections, like IC jacks, wall outlet/IEC inlet, tube sockets and pins, internal ground wiring faults, loose chassis ground screw, dirty contacts anywhere, can all be source of hum.
EMI is electromagnetic interference, usually stray magnetic fields from the power transformer, especially if the hum is 60Hz. AC power wires nearby signal wires inside the chassis, AC heaters, etc radiate noise that is picked up by the sensitive, high gain stages in the amp. These are design flaws and cannot usually be fixed easily. Low cost amps allow more noise to keep the cost down. Time to upgrade.
If you find that the amp is quieter when input is shorted, then there is a ground loop with another component. Look for opportunities to reduce resistance on signal, power and tube pin connections by cleaning and tightening these. If the other components are on different electrical circuits and are quiet when moved to the same circuit/outlet as the amp then check the connections in the outlets that cause hum. These can come loose and make a high resistance ground that can cause hum.
If you can't find the cause of the ground loop, or find that it can't be easily fixed, then you can still fix it with gadgets, like you alluded to above.
http://www.jensen-transformers.com/iso_aud.htmlModel CI-2RR for the interconnects. These are supreme quality transformers that break the DC connection to eliminate the hum on the interconnect ground, but the AC signal still gets through nearly perfectly, with only 1B loss.
http://www.jensen-transformers.com/iso_vid.htmlUse VRD-1FF if you have cable TV or FM radio antenna coming into the system.
http://www.b-p-t.com/http://www.equitech.com/To remove ground loop potential from your mains power, works especially nice on tube amps. These make a floating ground and other significant improvements in power quality. But heavy, expensive and the transformers usually make some mechanical hum.
