Quite large.I own the 9 mk2.It has been moved to center channel duties.(Bi-amp with Aerial-CC3)(bi-wire capable) While I'm not trying to say this is the best amp; I can modestly say it ain't bad.The original 9 was class B the9 mk2 was A.As I read thru different posts I can tell you it's better then what some folks use.The reason you don't see as many used is 2fold #1:It is one of those "hard to beat for the money" amps,#2 they didn't make as many as say AR or CJ;they don't make it any more.It has user friendly biasing;trim pots W/ leds.You can use EL34-6550,KT88.I have sets of ea.When the AR VT100 came out,I borrowed one for a weekend, a dealer demo.-sorry guys it wasn't nearly as musical it was harsh to my ears.Both amps being tube,I figure it wasn't a synergy problem.While I admit I am anti A.R., it is the dominant tube gear Co. Stereophile reviews EVERY PIECE they come out with.Gives it their highest ratings,and has little space for other products. This is why so many of us haven't heard of a lot of gear.