HP-46 - how do I set the mains voltage ?


I got a new toy today - my HP-46. My problem with this unit is, that it is set to 110 VAC (U.S. setting). I'd need to convert it to 220 or 240V (European setting). I know, that I have to change the fuse, but what's the clue with the PC card?

How do I change the setting ? Please help.

Here's some text from the HP-46 description here on the museums HP-46 page:

This was an AC-only device that operated at 100, 120, 220, or 240 volts at a frequency from 48-66 Hz. Voltage was selected by a combination of the orientation of a small (about a square inch) PC card and the selection of a fuse at the back of the machine.


Dave's Museum CD set has the HP-46 Operating Guide on it. I'd recommend getting a set because you never know when you'll get an old calculator or peripheral without documentation, and this set has nearly everything! Anyway, here's what it says about power:

"Before connecting the power cord to the back of your calculator, check the setting of the voltage selector card in the power module. The number visible indicates which voltage is set. The HP-46 operates on power line voltages of 100, 120, 220 and 240 volts ac, with a power line frequency of between 48 and 66 Hz. If the card is set to the available power line voltage, you may skip the next step and go to step three.


"To reset the voltage selector card: Slide the plastic window on the power module completely to the left; then remove the fuse by moving the FUSE PULL lever to the left. Pry the voltage selector card out (use a pointed tool such as a ball-point pen) and re-insert it so that the number representing the available line voltage is readable. Move the FUSE PULL lever to the right and insert the correct fuse for the new line voltage setting. Then slide the plastic window back to the right.

"NOTE: For 100 and 120 volts ac operation, use a 1/2 A. fuse. For 220 and 240 volts ac operation, use a 1/4 A. fuse.

"Plug the power cord into the back of the calculator and into a suitable power outlet. The calculator requires a maximum of 40 voltamps.

"Turn your calculator ON by pressing the LINE switch. Each time the HP-46 is switched-on, the word CLEAR is printed (provided PRT OFF is released). To switch-off the calculator, merely press LINE again so that OFF is visible.

"Your calculator meets current NEMA (National Electrical Manufacturers' Association) grounding standards provided that a 3-conductor power cord is used to supply power to the calculator from a suitably grounded outlet."

The manual also mentions that there were five different power cords (with different plugs) made for this calculator. The cord included was supposed to match the outlets in the area in which the calculator was sold. If the cord you have doesn't fit your outlets, the manual says to contact your nearest HP Sales and Service Office. However, I'd say the chances of them stocking HP-46 power cords at this late date are slim, so I hope you already have the right cord.



Hi Wayne, Thanks

I looked at it and found out where the PCB was yesterday. I just don't have a clue now, what fuse to take - slow blow or fast blow. I'll insert a fast blow for the first time. The U.S. fuse I got with the unit says 250VOLT (which is common for the small fuses) on one side and BUSSMDL 4/10 on the other side. 4/10 seem to be 0.4 A (for the U.S. setting), but what's the speed ?

BTW: the fuse requirement is written onto a sticker on the unit, so this wouldn't have been the problem.

Anyway, everything else is like I guessed it.

The power cord is a normal power cord found with a lot of equipment today (In German we call it "Kaltgeraetestecker"). This one's very common.

Thanks again for your tips.


I checked the manual again, and found a list of the spare fuses that originally came with the unit. They were:

1/2 A, 250 V slo-blo

1/4 A, 250 V slo-blo

Hope this helps!



Yes, slo-blow was the magic word. The other values are at the rear of the unit. I just couldn't decode slow or fast from the fuse. In German the fuses normally are marked with Voltage, current and "T" ("träge" = slo-blow) or "F" ("flink" = fast blow). I just didn't want to risk my new toy.

Thanks again


Glad I could help!

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