I have a VR that has started to sound quite terrible. It has lost power, tone, has no bass and is quite distorted. I replaced the power tubes, thinking that might solve the problem, but it didn't. All the pre amp tubes seem fine, but I haven't tried replacing them yet. What could cause this? The caps were replaced a few years back as well. Would a rectifier tube going bad cause this? If I cannot figure it out, to the tech it goes. Thanks.