I have just acquired an Audio Aero Capitole amp for demoing. It uses both EL34's and KT88's. I recently, today, changed out the KT88's for some 6550's. The 6550's do not have the base control of the KT88's but they do allow the sweetness of the EL34's to come through much more clearly, giving me the nearest to the C-J sound that I have lived with and loved for many years, only with much more articulation, detail, breadth and much else. Hope that helps.
