Turn on thump is a common phenomenon with valve amps. The solution: turn your preamp on first, then your power amp. That should fix the problem.
Help my preamp sucks in my woofer
I have an Audio Innovations tube preamp about 12 years old. When I turn it on, there is a weird sound in my speakers and my woofers move in at the same time. This has happened with three different amps so I believe its the preamps fault. With A tube amp, the sound was when I shut the preamp off not when I turn it on Now I have a solid state amp which runs in the always on postion all the time and the sound and woofer suck-in happens on turn on???