Mains adapter/charger for HP-67 and HP-65?

[n1msr]

I have an original HP mains adapter (UK 220V) that I use for my HP-67 and HP-65 calculators. I still have new but old (bought new in 1995) HP NiCad packs for these, so this works well.

However, if the mains adapter were to fail, I am not sure what I would do. I know that many have built more modern rechargeable battery packs, e.g. with NiMH and charge them outside the calculator.

Do you know if it is easy or hard to adapt a modern off-the-shelf mains adapter to work with these calculators? One tricky bit would be the connector that plugs into the calculator. Fabricating or re-producing that might be the hardest job, so I'd have to rely on the original I have.

I have googled things, and I see some quite detailed analysis of the circuits inside the calculators (e.g. HP-41 battery pack) and some detail on the 65 and 67 boards (the toroid transformer) but nothing about getting the mains adapter itself to connect to the usual calculator input.

Any advice/experience appreciated. Thank you.

Mark