I have been using the 12BZ7s (gray plates sound smoother than black plates) in my Jolida for more than 2 years. Significant improvement in my opinion; smoother analog-type sound with more presence with my MG 3.6 Maggies. The 12BZ7s draw twice the filament current (300ma per tube) as the 12AX7 so I had to mod the 12 volt power supply to protect the 12V regulator chip that is rated at only 1 amp. The 12BZ7s worked fine without the mod but pushed the regulator to its limit. (No issues with plate voltage or current) The 12BZ7 is taller so you can't use the tube shields. The tip of the tubes just clear the top cover and protrude slightly through the vent holes.
