KT120 question

[zintolo]

I think it was Messa who made a bass amp using six 5881s that was awesome.

Schematic shows six, but it was with twelve 6L6GC:

 

[Koonw]

Siegmund Big Boy 330 | handmade 330 Watt ultra-linear KT150 Bass Tube Amplifier
[SIZE=+1]6x KT120 300 Watts UL class AB or
6x KT150 330 Watts UL class AB[/SIZE]

 

[zintolo]

I saw it few months ago but... aren't those KT150 too close to each other? Also considering that, despite the fan, they are in an almost closed cabinet:
http://siegmundguitars.com/images/bigboybackgrill.jpg
http://siegmundguitars.com/images/bigboycab.jpg