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

[Dave Britten]

Conventional wisdom is that you're better off not plugging in your HPs these days. The 65 and non-programmable Classics are allegedly fairly resilient, but with the 67 being based on Woodstock technology, I would be very nervous about killing it if it's plugged in and the battery isn't connected securely.

I just use Eneloop AAAs in my Classics, with one of Mark Hoskins' excellent AAA battery cases:

https://www.ebay.com/itm/323932408596

A modern AAA NiMH (~750 mAH) should have capacity pretty comparable to a 1970s NiCd AA (nowadays 600-1000 mAH). You can get Eneloop Pro AAAs if you want 950 mAH.

I like this setup so much that I made a similar AAA case for my TI-59, though it's not quite as pretty as Mark's.

If you still want to get some use out of the NiCd packs you already have, I'd probably try to track down one of those HP spare battery chargers (or just make one, since NiCd charging isn't terribly sophisticated).

[John Garza (3665)]

As a rule, I externally charge batteries for all my LED machines. It's just safer and more foolproof that way. The little black HP 'Reserve Power Pack' is ideal for this and it even works for TI-59 style battery packs. And spare classic power adapters are available on ebay or if you've been collecting for a while, you should already have bins full of them. One series I do not have an external charger for is the 10/19C. I charge those with a small HP lab power supply where I can adjust both the voltage and current. Model 6214A. The original HP classic NiCds charge at 50ma - and that's what the Adapter connected to the Reserve Power Pack supplies. However, newer battery types may require more current sometimes in the charging cycle to charge properly. I generally keep 1000mAh triple cell NiCd packs for the classics and don't use the 2-3Ah NiMH cells so I can charge them with my existing equipment in a reasonable time frame (like 8-12hrs).

-J