speaker distortion

I recently built a Class A single-ended tube amp. I bought a speaker off Ebay, It came out of a organ (1968 cleavland speaker) The amp turned on fine, pilot lited up fast. No pops,whistles, or squells. Amp sounds good at lower volumes, nice full tone. Turn it up around have way, it has excessive bass, acts like the speaker is being overextended and way overdistorted. High notes sound clear and clean, but lower notes sound terrable. Amp has been played for atleast 4 hours. Is it the speaker? Sorry about the novel I wrote. Have a good day. Thank you. John