I think you'll find that low end response with tube amps will correlate with output transformer design. VTL amps excel in this regard. I have a pair of VTL 300 monos which provide the most controlled and musical bass of any tube amp I've tried. They built a few model options in the 200-450 watt range.
Must say I'll add my agreement with John that 200-250 are hardly "moderate power" but I would say for ANY amp.
Must say I'll add my agreement with John that 200-250 are hardly "moderate power" but I would say for ANY amp.