L/R poweramp hot---centre amp not, why?

[indus]

Apologies for the long title.

I have a Quad 909 amp firing my L and R (its about 140w).
I have a Quad 99 biamping my centre (80w)

Via the preouts of my Onkyo 875.

Speakers are MA GS20, and MA GSLCR.

After watching a film the 909 is often quite hot, the 99 never more than barely warm. I'm just curious, since the centre channel works the hardest, why is the 909 getting hot and the 99 not?

Thanks

[Mark.Yudkin]

You're driving two speakers with one 909 as opposed to one speaker with the 99. In addition your assumption that "the centre channel works the hardest" is incorrect when talking in terms of the amp (the centre does the the dialogue, which needs little power). In most setups the centre speaker is smaller (less bass), and power draw is inversely proportional to the frequency. The centre channel also has less transient peaks.

[lbstyling]

the class a bias is prob much higher in the 909 amp.(if its a more expensive amp than the cooler one -this is likely the reason.)
the trade off for higher class a bias is lower efficiency (roughly half)-therefore much more heat.