A good power conditionner with tube amps ?

I have to agree with Sns......IMO If you want to do something for your amps consider D-Lines, good wall outlets and power cords. Many find dealing with the ac part of the system can be most rewarding. Happy Listening!

"Not just my experience, read the threads, this has been gone over many times before. IMO, power conditioners are for everything BUT the amplifier."

This is not intuitive to me.

How or why does it negatively affect the amplifier's sound?

Mapman, I did state all the PCs I've tried diminish dynamics to some extent. This is heard as a rounding of transients, often very subtle, the music loses just a bit of life. While it sounds smoother, I'm just a bit bored. Take the PC back out and I'm engaged.

As for why. I suspect the transformer based PCs lose through all the additional wire in the transformer windings (and capacitors on AC outlets). I suspect others lose through additional capacitors, resistors and other circuitry in AC path. All these additonal components also color the sound to some extent. I've played around quite extensively with different capacitors, they all have their own sound. My own BPT 3.5 Sig. now offers the option of V-Caps on AC outlets, I'm sure it changes the sound, something I plan on investigating very soon.

I've even found the the minimalist AC filtering of two caps in series on AC outlet to color tonality and restrict dynamics on various amps. In a perfect world there would be no need for AC conditioning, unfortunately, my AC is so dirty the plusses outweigh the minuses for my front end equipment.

Dynamic needs for front end equipment is much lower than for amps, ie. not as impacted in this regard (although I've heard some argue they hear front end components dynamically restricted by PCs) I like the BPT as it is the least colored I've tried.

Check out the the power strip which improves sound at
Mapleshaderecords.com
To my ears, it actually enhances the listening experience, even including perception of transient speed and dynamics on the tube amps with which it has been paired.
Like some of this company's other offerings, there is a fragile physical quality which necessitates taking a bit of care with this fine product.