Different Model F XT keycaps affect sound more than you might think...

[Wazrach]

Hi guys, after experimenting with my keycaps, I found out something really bizarre. I decided to replace the keycaps on my very pingy US Model F XT with the keycaps from a 1984 UK Model. I noticed straight away that the reverberations were reduced dramatically. It doesn't sound as satisfying. The H key was the pingiest before I changed them, so I decided to put the original back on. The difference is night and day. I'm guessing it's due to the way the springs are seated? Maybe they have less room to vibrate with the UK keycaps?

Here is a demonstration of what I mean. First is UK keycap, second is original US keycap. I chose the H key because that's the pingiest.

https://www.youtube.com/watch?v=bd4ZLwc ... e=youtu.be

Comparison of keycaps. The UK one is on the left, US right:
https://postimg.cc/gallery/2by42pft0/?f ... RP9ze1xxv8

Typing demo of UK keycaps: https://youtu.be/fmVxkSEbaCs

Typing demo of original US keycaps: https://youtu.be/dGuC1zZJ9Yw


As for the actual board, I bought the assembly from Redmaus after asking to buy the pingiest Model F XT assembly he could find out of the 30 or so he picked up at Computer Reset. I'm guessing it's this way because the assembly is quite "tight" out of the factory. Usually, the middle row feels loose and spongy when the foam has deteriorated - but that's not the case here. The middle row is extremely crisp and firm, with no wobble at all, despite the fact the foam is literally just a paper-thin skin. The row below is slightly less crisp, and the bottom row feels pretty spongy. I can live with that.

It's pretty clear that the assembly has been stored in a box for decades, but has still been exposed to the air. There's no dust anywhere, but the barrel frame is pretty corroded and rusty. Like I said before, the foam is non-existent.

It's a bit of a weird one. It has a shiny green backplate with no shop sticker, just two small stickers. It also uses F122-style flippers with rounded corners.

[Ellipse]

In my experience there is an important relationship between the key cap interior height (where the spring rests inside the key) and the spring free length if you want a good sound. IBM had varying measurements for this key dimension and it resulted in different sounds. A good match between these two components will yield a good sound.

The new key factory did a great job with this "key" dimension on the keys. Just now I measured 12.81mm on one of the new keys and 12.81mm on an original XT key - a good match.

Based on the key cap interior height the spring free length should then be adjusted to get a good reverberation sound. As part of the spring production R&D I have done so, and the new Model F keyboards have a good sound (not too loud and not too quiet). Also the new springs should get a bit more reverberant after a number of years.