New US-made KT88 – Actually, it's the GaNTube 88MkIII [$1'500/pr] from AGD Productions so a modular plug'n'play output stage in a glass bottle which switches at 800kHz and can upgrade their Vivace and Audion class D amplifiers. The redesign has extended bandwidth to 60kHz, increased output filter slew rate, lowered noise to -140dB and THD to below 0.003%. In the Vivace MkII monos, it delivers 250 watts into 4Ω and still 200 watts from the Audion's smaller power supply. Max peak current is 30A. In short, this isn't your dad's KT88 tube and in fact won't work in anything but AGD amplifiers. Casual onlookers who poo-poo'd Alberto Guerra's 'tube' decision as a frilly design choice now stand corrected. What other solid-state amplifier offers an output stage which the user can upgrade without a screw driver or soldering iron to enjoy ongoing tech advances and superior performance specifications? The closest thing would be socketed discrete op-amps in a solid-state amp's driver stage. But actual output stage? If you know of one other than AGD's, do let me in on it so I'm not telling porkies.