think of it this way...the more tubes in an enclosed casework the warmer it will become.
They run extremely hot. From my experience, this is normal. I have a VK-51SE and originally placed it on the bottom shelf of my rack. After a few days, the left channel was not playing. After I checked that all the tubes were working, I placed it on the top shelf to give it more ventilation. I have never had a problem since. Even with all that ventilation, I would not be able to place my hand on the top of the unit for more than 10 seconds. Since the 52SE also uses the 6H30s, I would think it would run very hot as well.
Please let me know how you like the 52SE. I am considering upgrading. Have you also tried the Audio Research REf 3? I believe it is the same price and has received a great deal of praise on this site.
I just went over and tested my BAT VK-50SE. The top plate has a large center section (maybe 75%) where many ventilation slots have been machined. Of course, this is right above the 8 x 6H30 valves, so this is where the heat is generated.
If I put my hand on the solid plate area outside the ventilation area, the metal is only slightly warm. On the ventilated area, the metal is much hotter - particularly towards the rear of the case. But I can put my hand on this area for some time - it's not so uncomfortably hot that I have to remove my hand.
Mine is on the lower shelf of a two shelf PolyCrystal rack, but there is a big gap (9 inches) between the amp and the top shelf where the CD player is.
Over the 5 years that I've had this setup, the warmth reaching the top (heavy duty) PolyCrystal shelf and the weight of the Sony XA777ES has caused the shelf to bow somewhat. Had I known that this would happen, I probably would have put the preamp on the top shelf.
I'd also like to know what you thought of the 52SE.