I just purchased a 41-C on ebay. The owners manual does not provide any information on an AC adaptor. Is there one for this calculator??

Second there is a small plastic cover on the right side of the calculator and it has two brass contacts. What is this for??



An optional rechargeable battery pack was available, and after removing the plastic cover, the "tunnel" allowed for the external AC adapter to connect to such battery pack. While the "gold balls" could have been used as a power connector, such feature never appeared in the market, and the gold contacts disapperared from later 41 models.

Except you are a very heavy-duty user, a set of 4 N-size alkaline batteries is the simpler, cheaper and mostly recommendable power source. Batteries could be obtained at Radio Shack, or as Eveready/Energizer E91, or Duracell MN9100, among other brands. Be sure about using 1.5 volt batteries, and not to allow batteries to fully discharge inside the calculator, as battery leakage will cause severe corrosion, perhaps the weakest point of the HP 41.

Congratulations for owning a wonderful machine!



actually, an AC adapter for the ball contact exists.
AFAIK it was made by a company called 'Corvallis Team',
a third party supplier of accessories for HP mobile products.

CT made some other nice things, like HP-41 port extenders, and a multiple outlet power source for HP-41 and HP-IL products, the CT 70520.



Hi, Barry;

just to add a few info to the ones Andrés and Raymond have already posted. I was lucky enough to collect two sets of these contacts - two brass (golden platted) balls, two springs (also golden plated) and a rubber support - and I use them in two 41 calculators: a CV and a CX, both fullnut models. AFAIK, all fullnuts are ready to use these contacts, but a few of them have the set itself, as mentioned by Andrés.

I use an external pack with four D-size alkaline batteries to power the calculator when using the card reader (and/or the optical wand) without worrying about discharged batteries. The worst case is the starting of the card reader pulling engine, a peak of current that exhausts the N-cells quickly. To power the calculator with the external batteries I use a home-made contact, a single-sided PCB conveniently cut. The copper surface is periodically polished and I managed to separate it in two parts ([+] and [-]) with a single cut in the middle. I added a plastic fastener in the isolating surface so both balls are pressed through the copper surface by the springs.

If you plan to use your HP41 as a "stand alone" calculator, a fresh battery pack will rest long enough so you'll forget it needs replacement (as Andrés mentioned, too). In fact, when you are a "first timer" in an HP41, the battery pack may rest for a few months only, because you'll want to use your HP41 too often... Never mind, we all here know what does it mean.

Congrats! You found a piece of the best Engineering available for its time that still amuses many people.

Luiz (Brazil)

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