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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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9th Apr 2020, 8:15 am | #1 |
Heptode
Join Date: Jun 2019
Location: Oxfordshire
Posts: 738
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Marks on 465B graticule
My trusty old Tek 465B has one of the fine metal mesh plates, and ever since I've had it it has a mark which will not come off with water or IPA. I suspect it's corrosion. I have an ultrasonic bath and metal cleaning fluid but I've been loath to try cleaning it that way in case it damages the mesh - as I'm not sure what the mesh metal is. Is this likely to be safe - what sort of metal is it made from?
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9th Apr 2020, 5:50 pm | #2 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Marks on 465B graticule
It may be lack of knowledge on my part but I would have thought that the outer surface of the CRT is plain old glass and that the graticule is printed on the inside surface. I do know that the 465B CRT has a metal (platinum?) mesh screen through which the electron beam passes but that is inside the evacuated glass enclosure. I suppose the screen might have some kind of non-reflective coating although I don't remember seeing a reference to such a coating in any of the literature.
Alan |
9th Apr 2020, 6:08 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,869
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Re: Marks on 465B graticule
It's a woven-mesh sheet in a frame that lies against the face of the CRT. Iknow the HP ones not the Tek ones, but it's removable once the bezel is removed.
They act to improve contrast , and at least on the HP ones there is a little grounding lug so that it works as an electrostatic shield for EMC emissions via the CRT face. I think the wire the screen is woven from is brass with a chemical blackening process having been applied. David
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9th Apr 2020, 6:20 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
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Re: Marks on 465B graticule
Is the mesh on the +outside+ of the graticule-plate, embedded in it, or on the inside?
If it's embedded or on the inside, you might be able to polish-out the damage using one of the kits available from places like Halfords for removing surface-discoloration from plastic headlamp-shields. |
9th Apr 2020, 6:51 pm | #5 |
Heptode
Join Date: Jun 2019
Location: Oxfordshire
Posts: 738
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Re: Marks on 465B graticule
David, the metal mesh could well be brass that's been plated. There was a sort of greenish residue on the mark which suggests copper in there.
It's only a minor irritation - maybe I'll try a bit of brasso and see if that works. |
9th Apr 2020, 7:09 pm | #6 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Marks on 465B graticule
Is the mesh removable? If so, would it be possible to post a photo? My standard 465B doesn't have this feature and just has the bezel with its blue acrylic sheet to provide implosion protection. There doesn't seem to be any mention of the mesh in the parts list. I'm intrigued.
Alan |
9th Apr 2020, 8:04 pm | #7 |
Heptode
Join Date: Jun 2019
Location: Oxfordshire
Posts: 738
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Re: Marks on 465B graticule
Alan, attached some photos. The first is with the cover removed showing the tube with its own (internal?) graticule.
The second is the mesh graticule on the left which sits between the earthing plate (centre) and the cover (right). And the last the mesh (cleaned a bit!) as it fits into the cover. Keith |
9th Apr 2020, 9:12 pm | #8 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
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Re: Marks on 465B graticule
Thanks for going to the trouble of taking the photos Keith. It's as if the mesh is an alternative to the normal blue screen protector. Not something I've come across in relation to the 465B before.
Alan |
9th Apr 2020, 10:46 pm | #9 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,350
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Re: Marks on 465B graticule
I think i first came upon these external metal shields on a Cossor 4100 'scope.
I have previously smashed up colour TV tubes (after first releasing the vacuum by carefully tapping the seal under the"valve base"). I have used a cut up piece of a delta tube's mesh on a small scope. It worked, but there may well be better sources of screening mesh. Les. |
10th Apr 2020, 10:25 am | #10 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,780
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Re: Marks on 465B graticule
The Tek 453 was often fitted with a mesh screen: they're so fine it's not obvious at first glance. Ditto (David) I think they're either brass or copper with a black finish. Ditto some marks don't come off! I find this type of contrast-enhancer the most effective in general.
John |