How can you tell if a recording is in mono?

How about disconnecting one speaker and see if you can hear everything coming out of the speaker that is still connected.
Would that work anyone?

If using 2 speakers the sound will be in the center between the speakers, no left or right sounds. The sound stage will be narrow.

Gawdbless, that could probably work, but it would be easier to just use the balance control on your preamp or receiver.

Some old tuners have a built-in scope, or you can use a seperate oscilloscope. When measuring right vs left on a scopes x-y mode, mono will be a diagonal line with no with, while stereo will be a diagonal 'squiggle' (for lack of a better word) varying in width.

Personally I hate mono and the early sixties ping pong stereo inspite of great music of the era - John Coltrane, Miles Davies, Sonny Rollins to name few.

I stay away from any recordings prior to 1959 and early sixties. IOWS, anything recorded before 1959 would be mono ( someone pl, correct me if I am wrong) I am talking about the ones available on CDs. As good a digital system I have (IMO), the re-mastered recordings ( classic jazz) from this era have that high freq tinge around analog notes that it is annoying. (may be the inorganic nature of the recordings has something to do with it) Same recordings played back on LPs are much more bearable though. Not great but bearable. I am referring to Jazz recordings. Classical recordings on the other hand from the early stereo era on Vinyl sounds great.

IMO, recording technique/s have come a long way ( excluding compression mastering taht is on going on commercial releases). May be I am getting way off topic....