Editing Hi-Tek Series 725 (section)

==Series 725 switches==
[[File:Space-invader.png|thumb|A space invader that the switches are named for]]

Series 725 is a family of [[metal contact]] switches designed by [[Hi-Tek Corporation]] in the early 1980s, and patented post-introduction in 1984. These switches are used primarily, if not solely, in keyboards manufactured by Hi-Tek and [[NMB]]. Series 725 switches are commonly known as '''space invader''' switches, due to their resemblance to the enemy characters in Taito Corporation's ''Space Invaders'' game from the late 1970s. The Chinese name for them is "怒熊", translating to '''Fury Bear''' or '''Angry Bear'''. The series was also referred to as '''NMB Hi-Tek''' when the relationship between Hi-Tek and NMB was not known. 

Series 725 switches are notable for having a particularly unusual [[keycap mount]] — the [[slider]] is large and flat-topped and the [[keycap]] clips over the top. The [[return spring]] reaches to the top of the slider, meaning that the keycap sits over and around the slider, reducing the height requirement of the keyboard significantly while retaining full travel (the switches are specifically patented as "low profile"). As a result, there is no upper shell, as the slider also serves this purpose.

Like the previous [[Hi-Tek High Profile]] switches, the slider contains a horizontal plastic bar that holds apart a pair of vertical electrical contacts, which close together when the slider is depressed or removed from the switch. Each contact has two legs, for a total of four arranged in a square.

The early switches had a rounded slider with a large opening at the top; this "soap dispenser" or "Gundam" design is the one featured in Hi-Tek's patent. The Series 725 keyboards featuring these switches lack the NMB branding on the PCB, and do not appear to have a manufacturing date on the PCB either.<ref>geekhack — [http://geekhack.org/index.php?topic=33130.msg1450817#msg1450817 What did you get in the mail today?]</ref> The age of the keyboard can be estimated by the lack of dedicated LED switches.<ref>geekhack — [http://geekhack.org/index.php?topic=60707.msg1499485#msg1499485 NMB Hi-Tek Space Invaders discussion topic]</ref>

Within a couple of years of their introduction, the more familiar "space invader" design was introduced, that was maintained for the rest of the switch family's production lifetime; the opening in the slider was reduced in size and made rectangular. The "eyes" in the slider help to visually determine the switch variation where the same colour has been used for more than one switch type.

As with the earlier Hi-Tek switches, the return spring has a tight cluster of turns in the centre as well as at each end.

Keyboards with Series 725 switches typically use a different switch for the space bar. The only difference is that the spring is longer, resulting in a stiffer switch.<ref name="HaaTa1">geekhack — [http://geekhack.org/index.php?topic=12861.0 Nmb rt-8251t]</ref>

Series 725 switches also use custom [[stabiliser]]s where the custom-shaped stabiliser wire clips directly under the switch shell.<ref name="RT101-3">Deskthority — [http://deskthority.net/photos-videos-f8/nmb-rt101-t4076.html NMB RT101+]</ref> There are at least two shapes of switch shell depending on whether a stabiliser is required, but the stabiliser version is used indiscriminately, probably to ease stock management. Reinsertion of a stabiliser wire can require de-soldering a switch.

Series 725 switches were introduced at least as early as 1985.<ref>Deskthority — [http://deskthority.net/keyboards-f2/picked-up-an-xt-keyboard-the-other-day-t3909.html Picked up an XT keyboard the other day]</ref> The NMB RT8255+ with Windows keys indicates that they were produced until 1995.