Besides frequent tube replacements, heat wreaks its havoc on other surrounding circuitry as well.
BAT Thoughts.....
i am a tube guy but my listening space get's too warm with the vk-55 tube amp. the vk-5i tube pre seems to be less of an issue. ever tried a tube pre/ss amp pairing? also, i will get another tube amp for the winter season and desire something with a bit more "creamy dreamy" presentation than the 55, which i found to be lacking in sound warmth (the unit itself could sure get warm!. the cary brand works for my ear but wondering if anyone has other thoughts?