I've owned 4B's over 23 years, they depend upon lots of unrestricted air movement for cooling, put one in a closed in area and it will get too hot to touch! they produce a lot of power, and summer, heavy use, restricted air all can and do add to the heat. However that said, if it is getting as hot as you describe, and its got lots off available air [I always put mine on at least 2 inch tall 2 inch wide 12 inch long blocks running front to back, always placed with nothing above or below] I have had this occure more than once, if its the same thing you have a slight service problem. the remedy is easily preformed by any qualified tech. it is a simple adjusment of bias, usually one side gets hotter than the other, bingo. However whatever the problem, do yourself a favor, take care of it asap, I have twice had post warranty repairs to 4B's the bills were in Can.$110.00 and $130.00 I have a Bryston preamp and 8 Bryston amps in my system, and I'm damn glad I do.
p.s. a favorite way to place a 4B is alone on top of a milk crate, the kind that used to make good record holders, that proclaim property of so-and-so dairy, non-dairy ones are available from wall-mart type retailers, painted black, and with lots of the sides cut out, the 4B fits like it was made to, and placed behind a speaker. after all the less speaker wire the better. [i use almost none even though crossed over 5 ways, using 8 amps] Lastly, this set up has actually cured me of a never ending desire to upgrade that had lasted over 25 years, since the first day of 2003 over 7½ months, and still absolutely satisfied.
