MOTM

I just can't resist adding to this thread.
Assume a filament voltage of 6.3VAC.  My old tube databook says about 
300mA per tube for filament current.  You would need a transformer 
with a primary of about 40 Amps at 120 VAC and a secondary at about 
550 Amps (assuming you run at about 80% capacity.)  If you use AC for 
the filaments the thing is going to hum like a SOB even if the 
transformer is located some distance away.  What size cable would you 
have to use to connect the transformer to the board?  Maybe two pair 
of 0000 gage?  It will be hot enough to easily fry eggs.  As someone 
else pointed out you won't need a microphone.  Try finding out which 
tube is microphonic out of 1539!  This thing would need its own air 
conditioner.  And thats just for the filaments!  Actual power 
consumption could be twice that.  You could series wire the filaments 
as someone else has suggested, until one goes bad and you lose 20 
tubes. (Like Chinese Christmas lights)  Maybe it's liquid cooled!  
Don't laugh, I've seen it done.  Looks like too much work to me.
Why not take the easy route and use superconductors and a liquid 
nitrogen cooling system for improved signal to noise?
From one of the old fart tube heads.