You can use a lower voltage if that's the idea. in fact you'll probably have   
   to if you want low enough value plate resistors to directly drive the mixer or   
   whatever. Making balanced is no sweat, feed the grid of one side, bypass the   
   other and tie the    
   cathodes together.    
      
   I don't usually send people other places but Audio Asylum has a "tubes DIY"   
   section for people who build their own amps and other tube equipment. Some of   
   them guys are pretty sharp and can probably give you good answers. They are   
   also familiar with    
   balanced lines but it might not be the same impedance, so tell them the   
   impedance.    
      
   The site charges nothing, installs nothing but a cookie, and the only password   
   requirement is 6 characters. Quite easy to deal with. And it has image hosting   
   for attachments to posts so if you don't, you can post an electronics question   
   there and if you    
   wanted to display the picture somewhere for people here for example, you can   
   just stick the URL in your post. That will reveal your nick there but so what,   
   people can get your real email here.    
      
   It does sound doable though, but the ECC83 might not be the best tube for it.   
   They might recommend a 6SN7 or whatever. If you don't use an output   
   transformer I think the tube will be feeding a lower impedance than it likes,   
   but I think it will do it.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)