Identify this vintage test device? - Page 1
Forum section: electronics / testgear

author: MathematicalJ
author_rank: Contributor
timestamp: April 25, 2021, 12:39:22 pm
content: I acquire this vintage device recently but can't figure out its purpose. What does it do? How does one use it?More pictures:https://photos.app.goo.gl/xoznhMZgnGXAP4BS7I haven't opened it up yet.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 25, 2021, 12:43:23 pm
content: I think it's just a potentiometer with taps instead of a knob.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 25, 2021, 01:08:06 pm
content: Here's some description for that box:https://www2.humboldt.edu/scimus/HSC.54-70/Descriptions/L&N_ShuntBox.htm

author: Nusa
author_rank: Super Contributor
timestamp: April 25, 2021, 01:19:49 pm
content: If you carefully open it up, you'll likely find precision hand-wound resistors and not much else. How precise I'm not sure. If you've got some decent test equipment you can find out.

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2021, 02:48:37 pm
content: It is a precision resistor box, designed as a "shunt" to allow current measurement with a potentiometer.

author: graybeard
author_rank: Frequent Contributor
timestamp: April 25, 2021, 04:43:41 pm
content: Quote from: TimFox on April 25, 2021, 02:48:37 pmIt looks like a current shunt to me as well.

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2021, 04:54:00 pm
content: Why is it still assembled?

author: Johnny10
author_rank: Frequent Contributor
timestamp: April 25, 2021, 04:56:44 pm
content: Yea, I love it! Its cool.Great Company

author: MathematicalJ
author_rank: Contributor
timestamp: April 25, 2021, 05:21:44 pm
content: Thanks, everyone! It's a gorgeous bit of kit. I wish they still made test equipment out of polished mahogany and chrome plated brass. I'll post some photos of the inside when I am able to crack it open.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 26, 2021, 09:22:53 am
content: I think the right place for the teardown pictures would probably this thread:Teardown: Standard Resistors. Not sure if that box is metrology grade, but IMHO it would fit in there.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 02:39:13 pm
content: It's not just a current shunt. It's a series of precision resistors so it's also a precision voltage divider. Do not exceed the current limit marked on each leg. Note that in a device like this, that those limits are VERY conservative and are calculated so that the I2R heating is only a tiny fraction of a degree in order to maintain the accuracy of the resistors. These aren't circuit boards resistors that can withstand 40 degree or more temperature increases.Note that some of the digits in some of the number are missing, so make sure you know what you're doing before you applypowerto it (other than just a multimeter). Is there a model number on it somewhere?I have a May 1941 ad for some L&N devices similar to that and most of it is rated at 0.1% accuracy. Their One Ohm Standard Resistors were rated at 0.0001% accuracy! Unlike some other companies, I don't think that L&N made anything that wasn't accurate. The lowest accuracy item that I see in their ad is still 0.2% accurate.I have a few pieces of similar old L&N and GR equipment that I want to clean up and put on display.Conrad Hoffman has a website that shows the internals of a similar L&N device. You should take a look at it.

author: TimFox
author_rank: Super Contributor
timestamp: April 26, 2021, 02:58:54 pm
content: Twoflower’s post above links to a description of this current shunt and its application.