can any stereo receiver be turned to mono?

thanks!

What audio source are you playing? If it is an external component such as a CD player, you can convert the input signal to mono using a pair of Y cable connectors.

If what you want is a stereo/mono switch to summing the stereo signal to mono, insert this circuit to tape-monitor loop, the tape-monitor button will become a stereo/mono switch.
https://www.vinylengine.com/turntable_forum/download/file.php?id=11690&t=1

Or use a stereo to mono converter box.
https://www.amazon.com/OSD-Audio-SMC21-Converter-Isolator/dp/B07FFBJ8KR/ref=pd_lpo_328_img_1/136-081...

Even easier, connect the + from both channels into one. +L and +R both go to chassis ground, so connecting L+R positive sums them yielding mono. This is what happens inside the Y connector. Either that, or the amp goes up in smoke. Which this being a receiver and knowing how I feel about receivers just may be my ulterior motive.

Only one way to find out for sure. 😂🤣

millercarbon - please do NOT give engineering advice that looks serious.   I understand that you might think this is a joke, but somebody may take your advice and potentially fry their receiver/amp.  You never want to connect two outputs of anything into a single target, especially if they are speaker outputs from an amp/receiver. 

Also, this is NOT the same thing as a Y connector.  It is perfectly fine to use a Y-splitter to send a single output to multiple inputs.  However, a special circuit is required if you want to "sum" multiple signals.