My 1st tube amp: transformer buzz audible 15 feet?

It is not necessarily the amp that is defective.

Does it make this hum regardless of where it is plugged in or what it is plugged into?

In my case, it was my apartment's cruddy power. The amp was a Nelson Pass designed and built FirstWatt F1. One of the best amps I have ever owned and lived with (the entire FirstWatt line is fabulous). The crappy receiver I had before the F1 didn't make this noise. Did I want the receiver back in my system? Heck no. I found the cause of the problem and fixed it. Thank you Humbuster and long live the F1.

I suggest systematically explore the issue until you determine exactly what the culprit is.

Regardless, I wish you a hum free existence.

I tried two other wall outlets and there was no change, so I don't think it is the polarity.

Previously I did have the identical model demo unit at home, and I could hear it but only up to about 4 feet. Mine is significantly louder. My desk is is centered behind the sweet spot seating, and I can hear it from the desk, with my ears 17 feet (I measured) from the amplifier.

This is NOT normal. Return it and get a full refund.

This is not acceptable and is ridiculous for them to tell you anything otherwise.

There are plenty of other integrated tube amps that will NOT give any transformer hum.

Return it NOW. The other thing to check is a loose tube socket. Touch the tubes with a wooden stick and see if one of them is resonating. If so, a socket may be loose. If so, then you return it. Either way, return it. The transformer is just a buzzer, get rid of it. The goal is less noise, not more. If they don't have better quality control, change brands. Jallen

What is your amp sitting on? I had a similar problem with a more or less new RM-10. It was my first tube amp as well and I could hear it 10 feet away. I had it sitting directly on a piece of ply on spikes on a rug over concrete. I believe it was resonating with the ply and amplifying the existing hum--and it was annoying as hell. I happened to have some herbies tenderfoots I wasn't using so on a whim I stuck them underneath the amp. Problem solved. I can still hear the same hum if I stick my ears right up to the amp but it's no longer audible from my seating position or even 2 feet out. Nothing magical about the tenderfoots, because I switched them out (tonight as a matter of fact) with some audio technica footers I have and same result: quiet. Try it ASAP. I suppose trying a different platform might work as well.

If it doesn't work then, as most everyone has said (and obviously correctly), return it.