I have a Yaqin Integrated Tube Amp for my M2 + 2 X EP400 'Audio Only, SACD System' that doesn't impart any distortion that I can discern at normal listening levels - 85 to 90 DB at my MPL:
Last year I bought a whole compliment of new tubes for it to use when the OEM tubes finally give out. I used them for a month until their warranty was up & then put them into storage. According to the fanatics on the various 'Tube Forums', I should have heard a dramatic difference in changing out even one tube let alone the whole bunch; however, there was no difference that I could tell. That exercise reaffirmed to me that I'm not able to discern any appreciable difference in sound except for speakers. That amp also replaced a SS Sony basic 2CH Receiver & again, except for some initial placebo euphoria, no significant difference to me as well.
As for my 'exlabdriver' user name. I'm a retired RCAF Pilot who flew the mighty Boeing 'Labrador' Helicopter in the Search & Rescue role for over 3 decades. Here is a pic of yours truly training over a crash response boat locally in the waters off of Vancouver Island (where I reside now). I'm safely in the cockpit:
And another one of yours truly again in action off the north end of Vancouver Island over cruise ship heading for Alaska:
Seems so long ago, ha!
TAM
