Teardown coming soon Vishay Model 1303 Ohmic Standard - Page 1
Forum section: electronics / general

author: Cerebus
author_rank: Super Contributor
timestamp: May 16, 2016, 05:06:40 pm
content: I was fiddling with something the other day which would have been much easier if I'd had a resistance decade box. So, as you do, I went onto ebay to see what I could pick up. Among the usual decade boxes I spotted a Vishay Model 1303 "ohmic standard", no bids, just under £40 GBP starting price. Long story short, it's mine for £40.77 GBP including postage and it's on its way to me. Once it arrives I'd do a teardown and post it here. I can't claim that I won't turn it on first as it's entirely passive.I had a hard time tracking down any information on it and with a serial number of 127 I suspect there were never very many of these made. I found some other pictures of this model and the 1304 model, which had an additional calibrated potentiometer. The wooden outer case looks exactly like those used by Mann for their standard resistors. Mann were taken over by Vishay in 1983. Curiously I came across a US patent, No 3,571,778, assigned to Vishay and titled "Ohmic Standard Apparatus" which has illustrations that look remarkably like the construction of the model 1304. If it is the apparatus described in the patent then it's filled with hermetically sealed bulk metal resistors, and should have 50 ppm (0.005%) initial accuracy, 5 ppm/year drift, 2ppm/C tempco and about 5pF parallel capacitance. If anybody has any further information on this, please share.Hopefully it'll be here in time for a weekend teardown. Meantime a picture from the ebay listing.

author: Vgkid
author_rank: Super Contributor
timestamp: May 16, 2016, 08:39:03 pm
content: Looking forward to the teardown. i rememer seeing one on ebay, and they wanted to much for it.

author: GraemeMurphy
author_rank: Newbie
timestamp: July 23, 2018, 10:37:36 pm
content: Did you ever teardown the box?

author: Cerebus
author_rank: Super Contributor
timestamp: July 23, 2018, 10:46:06 pm
content: I'd forgotten all about this. I've some pictures somewhere, I'll dig them out.

author: GraemeMurphy
author_rank: Newbie
timestamp: March 27, 2019, 08:59:43 pm
content: Hi Cerebus.Can you post those pictures please?

author: andymcc
author_rank: Newbie
timestamp: April 02, 2019, 03:34:46 pm
content: Here you go. This is the six-decade version, model 1328, serial 105. I paid a bit more than cerebus (£60) , and it's not landed yet, but fingers-crossed it'll prove to be a good investment. The resistors are the sealed-in-oil type and range from 0.001% to 0.003%.Pic #1Pic #2Pic #3Pic #4(EDIT: This forum seem to be removing IMG tags from my post, so some direct links to the pics added..)

author: 0.01C
author_rank: Regular Contributor
timestamp: April 03, 2019, 01:21:03 pm
content: Great resistance box

author: HighVoltage
author_rank: Super Contributor
timestamp: April 03, 2019, 02:26:19 pm
content: Very nice indeed, I remember seeing it on ebay.Would be nice to get some measurements to see how good it is after so many years.

author: jasongeo2@aol.com
author_rank: Newbie
timestamp: April 18, 2020, 02:37:37 pm
content: I have two of these. One is model 1304.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 18, 2020, 06:32:31 pm
content: You’ll find the Achilles heel in those units to be the ratcheting switches, the resistors will be spot on unless they’ve been overloaded. Once the gold plate begins to show signs of wear, the box will lose accuracy. The switch contact resistance is rather high from the onset and is taken into account in the resistor values, so long as the contact resistance remains constant, all is good.While the boxes were sold as secondary standards, many more where sold (and used internally) as part of calibration stations in the very early days of VRP when they had rep/distributors doing final calibration (trimming) of S102 chips to the desired values and doing final encapsulation and delivery to end users. That went on until about 1978 or so when the design of the basic device changed to allow automated calibration to the final value and it was no longer cost effective to do hand trimming.The units that were used in calibration stations tend to have switch issues due to the heavy, daily use.