Mesa Boogie Tube SPAX 12AX7

I was so very disappointed in these valves. I bought a complete set for my mesa boogie mk iV that is approx 12 years old, thinking that they would be more reliable, and that they would bring the amp sound quality back to almost as it was when it was new (or even better?) - how very wrong I was.
The clean channel and the crunch channel volumes dropped away significantly, and the sustain channel sounded so brittle it was painful. Certainly not the warm gutsy sound the amplifier had when I bought it, so I have reverted back to my old valves and the sound I love is back.
I played one gig with these SPAX valves and spent the whole night fighting with the amplifier to get any sort of decent sound - they are absolute rubbish and I am sooooooo disappointed to put it mildly.
The end result is that I now have around £200 worth of useless valves that I cannot return, and the only option is to maybe try and sell them on ebay. It may be that these weren't right for my amp, but might be OK for another , but since they bear the name mesa boogie I expected so much better - poor quality product.