Tubes are tricky with Logans due to the wide impedance swing presented by the panels ranging from 30 ohms to 1 ohm. The item to note here is NOT to get bogged down by the low 1 ohm load @ 20khz since there is little music (energy) to be reproduced in that area. Any well-designed tube amplifier worth its salt will be able to handle this load at this extreme frequency without problems. It would be another story if this 1 ohm load occurs around the midrange area (1khz - 5khz). With this requirement from Logans, SET are pretty much out of the picture due to the fact that they like to see constant, flat impedance curve instead of the wild swing of the Logans. I've been in contact with various well-regarded amplifier designers asking about a good tube amplifier dedicated to the task of driving the panels and pretty much got the same feedback from all of them: about 30 to 60 usable watts of push-pull, (preferrably) triode design will suffice. It's worth mentioning here that the designers include Mick Mahoney of SupraTek, Dennis Had of Cary, Victor Khomenko of BAT, Fred Volz of Emotive Audio, Gary Dodd of Dodd Audio, Paul Grzybek of Tube Audio Design, etc... The key is to look for well-designed, choked regulated power-supply in order to keep the input voltage rock solid regardless of the demands during tough musical passages. Now, given that the Vantage (or Summit) have internal bass amplifiers already, the sweet spot for a good, musical amplifier is around the 50wpc area in triode mode, up to 100wpc ultra-linear. On the solid-state side, 50wpc (or 100wpc) class-A power from Pass Labs or Monarchy Audio are more than you'll need on the panels.
