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Hi-Tek Series 725

Contents

Overview

Series 725 (alternatively 725 Series) was Hi-Tek Corporation’s DIN-compliant discrete mechanical switch keyboard series. Linear, tactile and momentary switches were offered; other variants included corner illuminated, alternate action, and higher weight for space bar. The series was created to meet German standardisation. So far there has been no evidence to suggest that switches were ever sold separately. As such, the switch designations remain a mystery, leading to various ad-hoc methods of naming the many variations. (Chances are, the variants would only have non-schematic numeric part numbers anyway, as with the preceding switch types.)

“One-eye beige” (older tactile type)
“Two-eye white” (newer linear type)
“Two-eye black” (standard click type)

History

Series 725 was introduced around 1983. The European patent was filed in 1984, citing a priority date of a US patent application from a February 1983 patent. The US patent does not seem to exist, as the US Patent and Trademark Office has no record of any patent with the application number in question.

From the examples collected by Sandy55 on his NMB Hi-Tek page, Series 725 remained in production until at least 1997.

Retooling

Not long after Series 725 was introduced, it was fully retooled, with the rounded plunger design being replaced with an angular style. One possible theory is as follows:

Premises:

  1. Series 725 production was initially set up in the United States
  2. NMB (later Minebea) moved the production to Thailand
  3. Shipping the tooling to a new country is time-consuming
  4. Production in a new factory will take time to get going

As such, it is possible that NMB felt that shipping the tooling to another country would be too much of a risk: it would mean a cessation of manufacturing for an undefined period, as any mishaps with import, installation, production etc. would mean an end to manufacturing output until it was resolved.

From this it could be suggested that NMB had replica tooling constructed and tested in Thailand, built to a revised and simpler design for cost efficiency and ease of construction (perhaps from what was learnt from making the original tooling) and once the Bang Pa-in factory was up to speed, the US tooling was scrapped.

There is, however, some doubt as whether this is exactly what happened. There is a Tandy 1200 HD keyboard with a switch type that falls in between the “US” type and “Thailand” type. It has the redesigned plunger style associated with Thailand, but the “eye” is circular (as with the “US” type) instead of square like the “Thailand” type. This example is marked as being manufactured in the US, and it has the same brand of support chips (Mitsubishi) as the earlier American example, instead of the Texas Instruments chips from the later Thai example. All three seem to be around the same age, judging by the dates on the ICs. It is as though retooling occurred in the US first, and then new tooling was made in Thailand first to an almost identical design to the US tooling. The suggestion is that the redesign occurred for other reasons, shortly before the takeover. It is still likely that fresh tooling was produced in Thailand, but it quite possible that this had no part in the change of design of the switches.

Specifications

The series name refers to the height at the centre of a home row keycap, measured from the bottom of the PCB, measured in thousands of an inch (0.725″ or 18.42 mm):

(The illustration above is from Hi-Tek’s product literature; see Documentation below.)

The following details are taken from the RT-8200W brochure. The force and travel figures are standard for NMB keyboards.

Contact body Spring temper phosphor bronze
Contact surface Gold alloy inlay
Pretravel 0.070±0.020″ (1.78±0.5 mm)
Total travel 0.140±0.020″ (3.56±0.5 mm)
Operating force 2.0±0.5 oz (57.1±14.2 gf)
3.0±0.5 oz (space bar)
Tactile force 85.6±14.2 gf (audible click keyswitch)
Rated lifetime 100 million cycles

Documentation

All documentation was provided by Susan Kennedy (formerly of NMB) and scanned by Benjamin Rockwell, except where otherwise noted.

See also