Stan: Check to see if it's the speaker voice coil or the audio output xmfr that is open. (Sometimes the output xfmr is mounted on the speaker itself, sometimes on or under the chassis.) To check the voice coil or the xfmr secondary, you'd need to disconnect one of the leads from the output xfmr secondary to the voice coil.
If an ouput xfmr winding is open, you can replace it and keep the speaker itself. If the speaker voice coil is open, then you'll need a replacement speaker.