Yup...I am aware , but MESA made the tubes to fit and BE INTERCHANGEABLE in these sockets and the use I have put these to is in the realm of reasonable...the PROPER tubes ARE IN the proper sockets...(Mesa says how to pair them...all we did was listen to them)(they NEVER SAID you couldnt mix types...only you had to use THEIR TUBES...and buddy...WE DID)..I DID NPOT interchange tube colors in the sockets they are intended for...THAT should be the only consideration...(meaning I didnt mix inner and outer...I kept them in the proper orientation and placement...there is NOTHING in the Mesa literature that says you cannot mix them this way)...now maybe they see this and speak up...then I WILL FIGHT WITH THEM because the tube sets they have are really NOT the greatest...or we wouldnt have to DO THIS!!!! ALSO forgot to mention...I never use 45 or 10 watt mode...worthless modes that sound like bass-less ****...the one issue I have with the Mark V is it is really not a very bass heavy amp and losing ANY bass destroys the tone!!! SO NO TO 45 watt and 10 watt mode(I wish they would give a mod to switch to 90 watt only and let us mix the el-34 and 6l6 like earlier Marks...it was the 10 watt mode that made them NOT pursue this in this amp!!! ( hate 10 WATT mode...the sacrifice for this mode was WORTHLESS)Maybe you're already aware, but the 10W mode uses the two left tubes (as viewed from the rear) and the 45W mode uses the inner tubes. Of course 90W mode uses all 4 power tubes. So, when mixing colors between inner and outer a cocktail of colors is actually being used for the 10W mode and the 45W mode would only use one of the colors. Not sure what effect this would have on amp performance or tube life etc.