bridging tube amps for mono

what affect does this have (if any...) on sound quality? clearly you get a power boost, but what are the pros and cons of using tube amp in this configuration?
Con...The amps will see a low impedance load, which tube amps are not good at. For example: if the speaker is 4 ohms you ought to be using 2 ohm outputs which most amps don't have.

I once modified a stereo tube amp so that it inverted one channel, simply by reversing wiring at the output transformer. My purpose was to drive a center channel speaker bridged across the amp, while continuing to drive the left and right speakers in the normal manner. (I made the thing into a three channel amp, without adding any circuitry). The setup worked very well.
so are you saying that i shouldn't get another auricle and bridge it.... ;-)

shaky understanding of circuits... why will a bridged amp see a lower impedance load? it's not the load that's changing is it?
Blakeaudio...One way to think about why the amp sees lower impedance is...when operating normally (not bridged) the amp is driving current through the speaker to ground. However, when bridged, the amp is trying to drive current, not just to ground, but against the output of another amp which is "pushing back".
PP stereo tube amp is possible to turn onto a full-function mono amplifier by connecting further in-parallel push and pull tubes between the channels and usning only one output transformer. That's how it's done in BAT tube amps. Just make shure the output transformer has enough of rated power which is in the most cases.