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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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17th Jan 2022, 3:44 pm | #1 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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Decade box maintenance
I have what I believe is a high accuracy decade resistance box from Genrad. I’m guessing it’s quite old and just wondered if there is any maintenance required. The switch contact are large brass things with multiple contact fingers. I wondered if a wipe over with DeOxit may help keep things clean and in good order. I was hoping to use this to test the resistance ranges on some DVM meters I have been asked to review.
Thanks Chris
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21st Jan 2022, 11:42 pm | #2 |
Heptode
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 901
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Re: Decade box maintenance
I recently restored a vintage decade box - more repair than maintenance!
The 3-blade rotating switch contacts have gouged slight troughs in each of the step terminals, although for my item the main issue was the slow brass oxide coating built up over decades of no use - which I resorted to 1000 grit paper to just remove to get fairly consistent readings. For maintenance I added a light switch contact cleaner/lubricant to hopefully suppress any change in contact resistance. Even so, sometimes I measured a slight variation in resistance, so moving a step and taking a reading may need to be done a few times to confirm the reading is consistent (certainly if you down under 0.1% tolerance). https://www.dalmura.com.au/static/GA...ance%20box.pdf Ciao, Tim |
22nd Jan 2022, 12:32 pm | #3 |
Hexode
Join Date: Nov 2006
Location: Biedenkopf, [Hessen], Germany.
Posts: 425
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Re: Decade box maintenance
in my Box made by Siemens is written to care the contacts of the switches with clean vaseline. It´s a laboratory class type, expensive hand work. The contacts are covered by a front sheet, not open
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22nd Jan 2022, 1:19 pm | #4 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Decade box maintenance
I've had can of DeOxit a long time, but I don't often use it. I definitely don't think that I would use it on brass. As above, a mild solvent cleaner with a lube, perhaps vaseline, sounds better to me.
B
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22nd Jan 2022, 3:29 pm | #5 |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Decade box maintenance
Similar question about cleaning decade resistor contacts on eevblog at the moment; https://www.eevblog.com/forum/repair...ve-to-deoxit)/
Looks as if the contacts are meant to be self cleaning in normal use, with vaseline or similar used to keep oxidation away from the bare copper or brass contacts. And avoid abrasive cleaning. I did note that Genrad use silver plating on some low resistance decades & every zero contact too. 1433 RESISTOR.pdf David |
22nd Jan 2022, 3:54 pm | #6 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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Re: Decade box maintenance
Ok thanks for replying. I had heard about Vaseline but wasn’t sure as it’s such a good insulator.
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22nd Jan 2022, 4:30 pm | #7 | ||
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: Decade box maintenance
Interesting IET still make the Genrad 1433 decade boxes, but the current range have solid silver-alloy contacts. https://www.ietlabs.com/pdf/Manuals/1433_im.pdf
The instructions state the following, if the decade box hasn't been used for a while; Quote:
Quote:
Looks as if the newer ones use all silver alloy contacts & older ones use bare copper for the 1k & above contacts, except the zero contact. See about the 9 minute into the eevblog video, not sure about his choice of standard WantonDestruction-40 at the end. https://www.youtube.com/watch?v=fKrvtYS_6fI David |
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22nd Jan 2022, 4:54 pm | #8 | ||
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Decade box maintenance
Quote:
B
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22nd Jan 2022, 5:39 pm | #9 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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Re: Decade box maintenance
I need too open up the boxes and have a closer look at the contact material. I may even see what the cost would be for getting the calibration checked
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