Replica HP-41cx



#7

I have lately bought an hp-41cx from ebay but it seems quite different from my old 41cv. The keys of the 41cx are brown and 41cv was black, keys of 41cx are dull and keys of 41cv were shiny, the material used for the keys seems to be softer on 41cx,you can feel the PRGM and ALPHA marks under ON / USER writings. Although the 41cx seems as newer been use the key clicks of my old 41cv is sharper. The 41cx is a halfnut withh serial number 2646s21781 and old 41cv is a coconut with serial 2402s42122. The 41cx is also working fine as well
Did any one ever heard about replica HP-41 calculators, becauce I doubt the 41cx I bought is an replica.
Thanks in advance


#8

No reason to worry.

If you check your old HP-41CV under neutral light, you'll see that it's brown, too.

Ok, it's a _very_ dark brown, but it's _not_ black.

The keytops have changed more than once, and also the actual switch mechanism.

From my experience, the units with the best tactile feedback are those from about 1984 up to mid 1986.

After that, there were production runs where the keys gave a softer feedback (mushy ?) .

And no, I didn't hear about HP-41 replicas so far.

Can you imagine how difficult it would be to re-make the production tools?

I think it wouldn't be profitable, as the market is very narrow;-)


#9

Units that have "mushy" keyboards is due to a manufacturing change.

There is a rubber sheet that lives between the keytops and the key snap domes underneath. This provides some quieting and mechanical dampening of the metal snap domes.

Originally, that rubber sheet was 0.016" (0.4 mm)thick. Over time, it was learned that the keys began to actually puncture the sheet and as a result, some keys would sit a bit lower than others. When the halfnut redesign came along, they doubled the thickness of that sheet.

With the 0.032" (0.8mm) sheet in place, the keys have to press through double the thickness of material to actuate the snap dome, making them feel what most call "mushy". Solved one problem, got another...

It is interesting to note that some early halfnuts had the thinner sheets installed, no doubt as an effort to use up existing stock on hand. No, I can't give you a specific serial number range of when the change over occurred :(

Between the fullnuts and halfnuts, the actual switch components have not changed, only that rubber sheet. The only change to the keytops was the early 41C "tall key" variant. They were the same slope as the earlier 30 series keys. It is also common in the early "tall key" models to have poor tactile feedback of the 1 & 2 keys. Changes to the heat stakes and the elimination of the circuit board hold down nuts corrected the problem.


Edited: 4 Feb 2008, 1:43 p.m.


#10

Many thanks for the clarification and detailed post:-)

So far I had the impression that the dome material had been changed over time, too...

Regarding the rubber sheet:

Would that punctuation cause any damage to the dome or the key tip?

Or is it a cosmetical thing only, having some keys rattle a bit?


#11

Quote:
Would that punctuation cause any damage to the dome or the key tip?
Or is it a cosmetical thing only, having some keys rattle a bit?

The domes never seem to fail :) I've seen perhaps two or three over the years but those were on units used outdoors for twenty plus years. The cracked domes still worked, they just didn't have any tactile feedback. This is same as to what happens to a classic when the key strip fractures. I've never seen a pin break off the key.

As I see it, the only real downside to the key pin puncturing the rubber sheet is that the key sits lower then those it surrounds and it has less physical travel since it now rests directly on the dome. This changes the overall feel of the key when pressed, it simply doesn't have the same "click". This failure, if you want to call it that, does not cause keys to rattle. With 11/15C's that is usually due to broken heat stakes with the entire keyboard becoming loose on its moorings.

FWIW, the original Voyager series all used the same 0.016" thick sheet. Well used Voyagers develop the same "low keys" as the 41 due to the key pin wearing through the sheet. They did not change the Voyagers to the thicker sheet for perhaps the feel issue. The 41 numeric keys are larger than the others, perhaps HP felt it was an okay compromise with the 41 but since all the keys are smaller on the 10 series, it just didn't have the right feel. I doubt we will ever know unless the original engineers pop up here and offer some sage wisdom.

The later and current 12C's did get a change in the rubber sheet to a harder material but thickness remained the same. With the harder material, the keys don't want to stick to the sheet, perhaps this is why the current units tend to have rattling keys. Just my theory.


#12

Thanks for the valuable information that you have supplied. The real reason that my first question has reised was the great quality difference between my old coconut and the new halfnut. I can even say that the poor quality of haflnut had disappointed me. Altough it runs properly it seems as if it is an home made calculator.


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