Leeds & Northrup -  Precision Test Set 5430-AM - Page 1
Forum section: electronics / testgear

author: Vtile
author_rank: Super Contributor
timestamp: September 06, 2017, 07:49:05 pm
content: One evening last weekend I were reading the history of tangent-bussol and man named Nervander (http://www.geophysica.fi/pdf/geophysica_1957_6_1_030_keranen.pdf). That lead to severe TEA symptoms (..and 200 pages of reading about the subject) and I did end browsing local buy/sell site, just before getting to sleep. Search word were Galvanometer (in finnish), I ended up bying L&N bridge in working mystery condition, the only hit for "Galvanometer". At monday I did drive to get it to the new home from an older gentleman, who as I understood had it as a retirement gift from his workplace or something on those lines.The older gentleman did show me the box, it were really worn out. Then I noticed the brass shields on it stating "Suomen kaapelitehdas". Interesting I thought, the gentleman said to me that " You can not imagine how much cable have been measured with this". Suomen Kaapelitehdas Oy were founded by Ab Gottfr. Strömberg Oy (now ABB Finland) and were later years know better as Nokia Cables (The mobile phone corporation in the later years) and now it is part of Prysmian Group. So the Bridge test set is most certainly made before 1967 as Suomen Kaapelitehdas were merged with some other small companies to form Nokia corporation. So I own a small piece of Finnish industrial history now.He also did show the internals and I could at that moment say that I do want the unit no matter the condition of the batteries at the bottom. The selling advert did say that the batteries need to be changed. I didn't even check the condition of those, put the cash in hand of the previous owner and quickly evaded from the property.Indeed the batteries are toasted.. Crystals every where around and one inside corner of the box.I ended up bathing the whole aluminium case to get rid of the leaked and crystallised battery gunk. You know that the measuring instrument is good when you can clean it with dishwashing soap and brush.I noticed that there were this foam bad in the bottom of the case, but as I soaked the case I noticed that it were paper (impregnated some how) and only extremely dirty (no text were seen through the gunk). The final threatment were to bath the battery compartment in distilled water for a few hours. Then I did dry it until next day and used compressed air to get rid of the moisture from some parts.While the case were bathing I did measure the bridge resistance a bit with my Keithley 197A, Kelvin setup. It definedly is in nice shape electrically only a bit of dust etc. The Keithley did agree with the decade knob set to 1x10 ohms.Both are in mystery calibration so the absolute value is something else. Isn't those rotary switches are a thing of art.... Leeds & NorthrupNow it is clean only small dot of oxidation is still there. I need to clean it more someday.I also made some picture manipulation magic on computer and printed a new instruction sheet to the top cover. As the old one were burned away in one corner as the case were repaired by welding.The instruction label inside the box re-glued in place and all clean and shiny first time who knows how many decades.This is how the real connector looks like, no that plastic rubbish here.Cleaned, assembled and ready for the service for the next 100 years or so.It did agree closely to all the 0.1% resistors I did throw in it. In picture 1.5K resistor. I did found one translated instruction sheet, that claimed that the guaranteed accuracy of these is 0.15%+0.01 ohms with internal 4.5 batteries, the external can be up to 200 volts. Don't know if it is true, but according my quick tests this unit is in those specs more or less. Hooray.Now, I need to test it more. I didn't get any phase shift what I tried to measure, up until 1MHz with sinewave and series resistor. User error or is this really so parasitic free (compensated). Hmm..Now I go to play more with the new toy.