Will a tube amplifier have hum or noise?

Silence when there is no music playing and minimal interference with the program material is of course an ideal condition for any high fidelity stereo system. Many tube amplifiers have some small amount of hum that can be present either from magnetic induction from the power transformer into other parts of the amplifier, or in other ways. Interference from certain poorly-shielded electronic devices placed nearby can also get into the tubes and become audibly noticed.

I design and test my amplifiers to be as silent as possible from hum or other noise. If you place your ear very close to the speakers, you may still hear a small hum, but this should not be noticeable from a normal listening position. Certain types of tubes, in particular directly heated triodes such as the 2A3 or 300B, may use alternating current (AC) to power the filament that is also acting as the cathode passing current through the tube. To control hum in my 2A3 amp, I add a potentiometer or "hum pot" which is a variable control to balance the filament voltage so that the hum cancels itself out and the amp can be very quiet.

Finally, there can also be some amount of mechanical noise in a tube amplifier inside the power transformer, choke, or tubes given some parts of the design where current is fluctuating at some frequency or a filament is heating up to a high temperature. Again, perhaps audible in close proximity but should not be a concern for listening. All this to say, is a tube amplifier a perfectly silent device? No. But is it a beautiful analog device that makes amazing music nonetheless? Heck yes.