Hello
New to the forum

I have a Peavey Transfex 208s-(25 watts X2) with problem.No sound comes out of the left speaker.Speaker is good when I swapped the wires from the working one.
Now when I plug my headphones into the stereo phone jack, I get stereo sound.I verified its stereo by changing the left/right effects levels.
Question is, does  the headphone circuit normally tap off the preamp or tap off after the power amp?
The amp uses 3 lm1875t power amps.Just wondering if its just a matter of replacing the amp that feeds the left.But if the headphone circuit comes after the power section then it seems that the power amp for the left is fine and its some other dubious problem.
Since the speakers do cut out when using headphones, is it possible the phone jack is at fault? 

TIA
Doug