41C external power options?


One of the features of my 71B and 50g that I really like is the ability to power externally. What are my options to do this with the 41C? (I did search and found rechargeable solutions, is that all there is/was?)



Early 41C units had spring-loaded contacts in the side "tunnel" that were intended for an external power adapter that HP never sold. The only external power solution HP offered was the 82120A rechargeable pack, which would accept an 82059A charger (or the equivalent for other regions).


HP didn't sell a wall adapter for the early C's with "gold balls",

but a Company named Corvallis Team sold an AC adapter with a suitable slide plug.

I can upload a photo of that adapter on request.




I can upload a photo of that adapter on request.

Thanks. Requested.


Here you are:

And while we're at it, a pic of some of the famous multi-outlet AC adapters from CT (CT7050, CT70520),

to which one can connect an HP-41C and up to three peripheral devices at the same time:




I just read the 82120A docs, but it was not clear that if I run the calculator while connected to power that it will run indefinitely. I am assuming that it will.


cheater cord 1

cheater cord 2

cheater cord 3

I was talking to Richard Nelson about the power connectors and he came up with the following recollection relating to the cheater cords listed above:

"PPC was the primary promotional force for HP-41 users to power their machine using a readily available so called TV "cheater cord" and a sharp knife to trim some rubber off to make a nice fitting connector. You would cut the rubber off on the "D" side of the connectors. A very common DC source was a lantern battery which cost $2 at the time. Do you have a reference to the PPC article and date or maybe a picture of the modified cheater cord."

Hope this helps, of course the cheater cable could be hooked up to an appropriate adapter.

Cheers, Geoff

Edited: 7 Sept 2009, 6:32 p.m.


In my HP-41 Input Output Board & IL2000 Interface System I describe a solution for an external DC power supply box for HP-41. Furthermore this solution includes a small add on circuit for switching on the HP-41 by an external event....

Best regards - Christoph Klug


Thanks. I have your book. What page?


Dear Egan,

Please refer to I/O-Board manual Chapter XIII.07

In Chapter XIII I describe a small circuit which activates HP41 by an extern signal (galvanic isolated with help of an opto coupler).

In Chapter XIII.07 I modify the HP41 battery holder with a small +6V backup battery and an 5 pin terminal for external DC supply. I add an micro switch for selecting internal backup battery or external DC supply. The micro switch is activated when the external cabel /harness is pluged in ....

This extenal Dc supply application is helpful for long time interface applications - and for advanced interface applications which need an wake up of the handheld by an external event - and last not least I use the external DC supply when burning ZEPROMS...

Best regards - Christoph


Excellent. Thanks.


I use my MLDL2000 with an external 6VDC adapter. This is directly connected to the BAT line of the module connector. On the HP41CX and CV there is some voltage drop, resulting in the BAT annunciator being on, but this is not really a big problem. Of course, this can only be used if there are no batteries in the calculator!


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