I'd suggest calling VTL and asking them. I believe they are quite particular about the tubes they use, and will have some suggestions that would help. One of the best things about the high end manufacturers is that you can call them and speak with someone who knows what they're talking about, or who may even have designed the unit. Take advantage of it.
Beating the Tube Rush
The tube rush from my preamp is more than I want. For most kinds of music I listen to, it remains unnoticable. However, thanks to a recent classical buying spree, and although the dynamics are stunning, during the otherwise quite spots the tube rush can be noticeable and annoying. I retubed the pre (VLT 2.5) 3-4 months ago with Mullard NOS--and that was a significant improvement across the boards--but after a few months the tube rush had crept back up to noticiable levels from my listening position (which may very well not be as far away as it should be, but I'm stuck with it for the time being). Does anyone have any great tricks or hints for beating this, or it is just the nature of the beast? (Yes, could go solid state, but I'm pretty addicted to the sound, so is there anything less drastic?). Many thanks.