Line in on my 65 2-10
         jochen.wendeba…
      
      
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 It's to the right of the extension speaker jack. Is it stock? How do I use it???? Do I even want to???  | 
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 The stock MM 210-65 did NOT have any such jack on it, so yours is a modification and an unknown quantity unless you open the amp and figure out what it is!  | 
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 Since there is only one jack, my guess would be that it is a line out to provide a line-level signal for a PA or recording feed but I would certainly be careful about testing that assumption!  |