I have had the VTL MB450 as part of my system. They did not hiss. But, they blew a lot of fuses. This was caused by a bad tube. No easy way I could tell what tube was bad, so I had to replace all of the tubes on the amp. That became very costly. I have replaced the VTLs with the BAT 150SE
amp. This amp has self biasing tube technology and you can easily identify which output tube is bad and replace as needed. These amps do not hiss. They just sound fantastic!