Marks on 465B graticule - UK Vintage Radio Repair and Restoration Discussion Forum

Keith956 · 9th Apr 2020, 8:15 am

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?

ajgriff · 9th Apr 2020, 5:50 pm

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

Radio Wrangler · 9th Apr 2020, 6:08 pm

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

G6Tanuki · 9th Apr 2020, 6:20 pm

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.

Keith956 · 9th Apr 2020, 6:51 pm

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.

ajgriff · 9th Apr 2020, 7:09 pm

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

Keith956 · 9th Apr 2020, 8:04 pm

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

ajgriff · 9th Apr 2020, 9:12 pm

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

MotorBikeLes · 9th Apr 2020, 10:46 pm

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.

John_BS · 10th Apr 2020, 10:25 am

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

9th Apr 2020, 8:15 am	#1
Keith956 Heptode Join Date: Jun 2019 Location: Oxfordshire Posts: 737	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? Attached Thumbnails

9th Apr 2020, 5:50 pm	#2
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	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
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

9th Apr 2020, 6:20 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	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
Keith956 Heptode Join Date: Jun 2019 Location: Oxfordshire Posts: 737	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
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	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
Keith956 Heptode Join Date: Jun 2019 Location: Oxfordshire Posts: 737	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 Attached Thumbnails

9th Apr 2020, 9:12 pm	#8
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	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
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	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
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,779	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