Products > Test Equipment
History of Tachikawa (TMK)
langlv:
Hello joeqsmith,
I got a TMK 100K, with design very similar to Simpson 269. I found a schematic on another forum, but in my VOM there is an additional relay (for overload protection?).
Hope you have some info abit it.
Best, and Happy New Lunar Year
Lang
joeqsmith:
I don't see a relay in the schematic you linked. Maybe you could trace that section out and post it. We may be able to sort out its purpose from that. I found a link showing a few pictures of the meter and talking about the 269.
https://www.vintage-radio.net/forum/showthread.php?p=746757
langlv:
Finally, it's not an overload protection, but a buzzer for continuity test.
The buzzer is not in part list, and is drawn as very discret circle in the schematic.
To achieve 10uA FS, the coil is quite large, almost 1 inch. I guess they did not make enough strong magnet. It's incredible that Triplett managed to build a 1uA FS with a smaller coil.
joeqsmith:
Funny to see the chain drive. Looks like a gear split. I wonder if you could have a set made from brass.
coppice:
I used to own a TMK 100k. I don't know where it went. It was an excellent instrument. The only weakness was the handle mounting. The bolts holding it could work undone, until you applied something to stop them. That chain drive approach allowed for a really nice layout inside, although like most multimeters of the time it must have taken someone quite a while to build it. I liked the way they tuned the 10A shunt. :)
It does have a buzzer for continuity, and it does not have overload protection. It has a nice wide resistance measurement range, but this requires a 15V battery which is probably hard to find these days. The use of a large 1.5V D cell for the lower resistance ranges kept the battery life high when using that buzzer a lot.
Being so sensitive, but with a really long pointer, you really need to use the meter damping "off" position when moving the meter, or it might prove a bit fragile.
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