Circular Output Amplifier Terminals.

Cardas Patented Binding Post
https://www.moon-audio.com/products/cardas-cpbp-crs-binding-post

VAC has been using them on their top amps for a while. They’re GREAT for spades, even 2 sets of spades. No wrench required. IIRC they’re Euro compliant because you can’t accidentally cause a short-circuit by touching + and - spades. But you have to drill a hole in them to accept bananas :( 

Edit: Or maybe Speak-on as others mentioned. Those are neat too. 

These?  They are SpeakONs.

So your amp accepts bare wire for speaker connections. And that Circle to the left of it looks like a freaking tube tester. But I'm just guessing. 

Here's the picture that I thought attached before.  Try again.  It's some sort of aftermarket mod to an ARC D-70 amp.

Still didn't post.  Not sure how to do it.