Brings back memories. A neighbor replaced his Stromberg Carlson integrated amp with some solid state stuff, and gave me the old tube unit. I didn't have any stereo speakers, or speakers at all, but decided to improvise. It was my first 'audio' project. 1967 or '68.
I found a round (probably 5" or so, I don't recall where I got it) paper cone driver, mounted it in an empty Maxwell House tin (the larger can), stuffed it with insulation I scavenged from a house under construction, poked holes in the tin's lid with a nail, using that as a grill. Sounded horrible, but I was very proud of it.
I used it with a pocket transistor radio headphone out jack, into the Stromberg's line input. AM Top 40 never sounded so bad. No bluetooth, because that hadn't been invented yet!