I've used these for years on my Fender Bassman 300. The most powerful amp I have ever owned. The sound was organic and 3D. Much better than stock Sovtek. I used a ring on them which reduces vibration and micro phonic effect, because you know a bass amp is not a picnic for tubes. This application is rough time and this amp played in studio almost everyday but did not get out much. The tubes suffered about 2 years of this abuse. Not bad! I'm telling ya, it's rated 300W on the back of the amp, but when those tubes glow, the lights are dimming. That's the juice they can take. Compared to a solid state amp, 6 of those tubes can produce equivalent of 900W. Nothing sounds like tubes.