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      DO NOT LEAVE A DECPACK IN THE RK05 It will be damaged and likely damage the drive as well. Someone will have to open the case and check on the heads. Don’t do it!

      Pretty sure you can just put a new battery in an RL.

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        What kind of batteries do they use, anyway?

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          According to the illustrated parts breakdown (pg 18 item 38) the battery pack is a 4-cell battery, p/n 12-10641-00. And according to this 27-year-old post, those are 4 NiCads in series. So replaceable, but not quite off the shelf?

          The most amusing thing I learned from all this is actually the little elapsed-time indicator on the back of the device, used to tell the user when the 1500-hour maintenance interval is up. It’s a column of mercury with a little index bubble in it, and the index slowly worms its way along the mercury column. At the 1500 hour mark, you pull out the indicator and flip it around, and the index starts heading in the other direction.

          They work by electrolysis - the index is actually a droplet of electrolyte; when you pass a current through it, the mercury on one side of the bubble starts dissolving into the electrolyte, shortening that column; and more mercury plates out as metal at the other side, making the opposing column longer. It’s ingeniously simple and apparently you could buy these things as recently as 2002.

          Compare and contrast with the safer solution that succeeded it, the electromechanical counter, which is much bulkier, and much more complicated.

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            It’s a column of mercury with a little index bubble in it…

            …that is really cool. I wonder if we could do this with something other than mercury? Worst case, gallium with a small heater in it…

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          IIRC, it’s a standard kind of cell - AA or AAA?

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      Kinda interesting that they chose RT-11.

      PDP-11 could run more interesting operating systems like RSTS/E - although I guess RT11 might be simpler to get up and running with.