connecting mono amps to pre amp

"then you would bridge the common/negative on the speaker terminals"

No, use "COM" terminal on left channel output to speaker negative, then if your speaker is 8 ohms, connect "16" terminal on left channel to speaker positive. Also, connect a jumper from "16" terminal on the left channel to the "16" terminal on the right channel.

Not sure why manual shows 2 speakers connected in mono operation, however I’m reading the instructions for my comment.

Thanks, Tony (Tls49). As you realize, my comment and the one by Mb1audio02 did not address the connections between the amps and the speakers, since they were not asked about by the OP. The manual you linked to indicates that for mono use the two channels on each of the amplifiers are paralleled, so what you stated in the last paragraph of your first post is correct with respect to the speaker connections. It should also be noted, though, that the tap which should generally be used (assuming the speaker’s nominal impedance rating is reasonably accurate, which of course is not always the case) corresponds to the nominal speaker impedance multiplied by two. In other words the paralleling of the channels results in what is designated as the 16 ohm tap becoming an 8 ohm tap, and what is designated as the 8 ohm tap becoming a 4 ohm tap, etc.

I would expect, though, that connecting the speaker to the appropriate right channel terminals and jumpering the right channel tap that is used to the corresponding left channel tap would work equally well.

Best regards,
-- Al

Thank you all!!! You guys are a plethora of knowledge!  never have had the opportunity to utilize mono application in my younger years,,,,LOL. have a couple of tube amps that I'm using with a mac c26, but using those to bi -amp a set of paradigms so  a little different than trying to do the MONO thing. Thanks again!

You're welcome, 2channeladdicted.  Just be sure to keep in mind the following statement in the 2120's manual:

Should the MODE SWITCH be left in the STEREO position and the output transformers be strapped for a monophonic load, one channel will attempt to drive the other and cause circulating currents and overheating. Be certain that the MC 2120 is never operated in the stereo mode with the outputs connected for monophonic operations.

Regards,
-- Al
 

So it should be placed in the MONO mode that has MONO(L+R)  Correct??