I think a certain amount of hum is normal. But for example my Dual Rectifier is much much noisier than my QR. My QR is pretty damn quiet.
There are so many things that can contribute to hum as Jack is pointing out. And that hum can have a cumulative effect as well. I have spent countless hours tracking down hum and it didn't get any better when I got an ABY pedal to play the QR and Recto together.
For context:
I now have NOS Chinese square getter preamp tubes in the QR (thx to
@just42dave )
I run a volume pot in the loop of the QR set to say 7/10
My guitar goes into a Boss NS2 suppressor and then back into the loop of the QR
I have 4 pedals out front going into the ABY including a wah and 2 boosts (one is an SD1 which is buffered)
The ABY connects 3 amps actually including a Peavey Vypyr 60 combo on pass thru mode - rarely turned on
All amps and pedals are all fed by the same wall outlet (very important). If you don't do that you introduce ground loops for sure.
I do NOT have any kind of power conditioner, or filters etc. But I do know I get continuous steady AC - which is important.
I can turn on a bunch of pedals, including the loop, and the amp is still relatively quiet.
I stand fairly close to my amps, and the MIM Strat can get a bit noisy (60 cycle hum) if pointed in the wrong direction
I have an MXR10 band EQ in loop of QR but it doesn't really affect hum
My pedal cables are all bunched up under pedal board as well. Some would say to separate those more and maybe even run power perpendicular to patch but that's another rabbit hole I don't feel like tackling.
I do run a ground lift on the Recto (3 prong to 2 prong converter) but that is not technically the safest thing to do