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Differential amplifiers?

8/1/1997 9:47 AM
Erik M. Wood
Differential amplifiers?
I am curious about tube differential amplifiers. I discovered a website which describes some pretty interesting designs for tubes. Included are your basic single ended design, balanced differential, cascode and bridge circuits, all of which are touted for their relative benefits and deficiencies.  
What I do not understand, is how when you have two parallel triodes, cathodes tied together, then both of them in series with a single resistor to a negative power supply (B- equal to B+), as in a balanced differential design, how an input signal to either grid will produce (as they describe) equal but out of phase outputs at the two plates (tied to B+)? Could someone please explain to me how one of this identical pair of triodes will be in phase with it's input while the other will be out of phase?  
I am of course assuming that in a single stage triode, the plate output is 180 degrees out of phase with the grid input signal, no?  
By the way the adress to this website is:  

R.G. >> ... how when you have two parall... -- 8/2/1997 8:59 AM