A month or so ago I was able to "steal" a YBA-1 from a local store...they had no idea what is was, felt the Blue Book value was incredibly low...and the rest is history. Kind of a road warrior, had only one 6CA7 in it...I suspect that one was pulled to lower the volume...but all the tubes were original Phillips... This thing is so loud, we really can't play it above about "1" in the basement. Yesterday we took it and a Traynor 6 - 10" cab (we had also "rescued") outside and frankly we couldn't get it much above "5" before our ears were bleeding...any distortion we heard had to be our ears! I have worked out that this amp is probably a 1970, about the time that the Bassmaster "Mark II" came out and I am wondering if that is what this girl really is...90 watts RMS out of two 6CA7's...whew! No fan though, so maybe not... This thing is really much too loud for anything my son and I will ever do, and am thinking of doing a master-volume mod on it, adding the control where I took out the ground switch.