My Belles 150 is buzzing when I turn it on..

Before making such test, as you've just did, I would thoroughly check if you can turn this amp unloaded at all especially for the long time.
Some of amplifiers may go to the high level of oscillations when no load is present hence buzzing takes place originally at collector output circuits of power transformer which IS quite distructive!
You may use a dummy load resistors(I guess you should get 25...50W/10Ohms) I always conduct such tests of reserviced amplifiers and once-in-a-while I burn them literally seing some smoke comming up due to some mistakes taken place during circuit repair or re-mount.
For you I'd suggest connecting such dummy load resistor 50W in your case(available at partsexpress.com or percyaudio.com). Turn on your amp with resistors connected at both LCH, RCH terminals wait and listen what's goning on:
if you see smoke, than something is a-miss... if you se no smoke than try to touch resistor but first bring your fingers close enough to the resistor surface to make shure you're not feeling the high heat. If the resistor is quite warm or hot than you're probably having the case with oscillations that you'll need to take care off either yourself or with experienced tech.
The reasons could be various with no exempt to shipping damage(the solder joints may get loose because of age and stress.

Sometimes a very low level buzz that can be heard from less than a few feet away is considered normal. There are several other possibilities, let the amp warm up a while and it may go away or there is a light dimmer or some other control in the house that is causing this.
My Belles 350a makes a noise on start up then goes away after about 2-3 minutes. I had a 150a hotrod that made a slight noise at start then went away within a few minutes.
I consider this pretty normal stuff.
BTW, I wouldn't turn on the amp without a load. I don't think it will hurt this amp but some will do as Marakanetz above says and some will just blow the output transistors.

Sounds like you make have some transformer hum, a very common problem without a single/simple solution, and which poses no real problem for you if you can't hear it from the listening position. Could be the transformer has become loose, could be caused by the the incoming current, etc. You could lift the lid (after a long turn off so the amp is tatally discharged) and check the connections of the transformers to the amp frame and or your could mass load the transformers/amp lids to reduce the resonance. You could also borrow a power conditioner to see if that would help. Hope that helps........

I owned a Belles 150a Hot Rod for a couple years and it hummed anytime my power supply was polluted by line noise from appliances, etc. This amp seems inordinately excited by such noise! Try to see if you can trace any correlation to lights, motors, etc. turning on. I talked to Dave Belles, the designer, about this issue. He more or less just shrugged it off with the observation that toroids are prone to buzzing & humming in certain circumstances.

more than likely transformer noise. quite common with that model.

mike

I have an OCM 500, the older sister to the Belles 150. It used to buzz a bit when I had it plugged into a different outlet. I also noticed the buzz would change as certain other things in the room would power on or off (e.g. a vacuum cleaner).

I eventually plugged the amp into the amp outlet on the same Monster AVS 2000 as all of my other components (which are plugged into an HTPS 7000) and the buzzing went away. I know what is said about not plugging amps into power conditioning which is why I originally had it straight to wall on a separate plug, but the buzzing was too annoying for me. I don't know if it was specifically the AVS 2000 that made the buzzing stop or (effectively) putting it on the same wall plug as everything else. In either case, I'm happy with it now.