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