John at Champ Electronics in Nottingham England has prototyped a 1000w tube amplifier using the beastly 813 tube. The 813s have a staggering plate voltage of 2500V DC and the quartet puts out an astonishing 1015w RMS.
I'm not certain what the musical application for this would be, but for the sake of all our hearing, I think it should be kept out of J. Mascis's hands at all costs.