On the Canadian side of things, Bryston is very similar to Klipsch, when it comes to customer service and standing behind their products.
Just phone them with the serial number and they'll give you the skinny on the 4B.
Very reliable amp, home or pro use.
You can send it in, not just for a check up/tuneup,but upgrades are also available to take a regular 4B and transform(LOL) it into as ST or SST version.
However, as with all great companies, times are a changin', the warranty periods are getting shorter, a long time wizard, head tech has just retired as well.
He used to not only service Bryston products, but whatever you brought to the main Bryson outlet/factory.
Had a pair of Crown D150's serviced and tuned by him.