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From: frank on 12 Sep 2009 13:12
Jim Yanik <jyanik(a)abuse.gov> wrote:
>>
>
> could be a geometry problem with the CRT;
> input a square wave signal,one cycle per division,turn up intensity to see
> the (fast)rising edges,and check for distortion.

the vertical edges are straigth on the "good" part of the CRT area, they
just aren't focused, look a bit broader than the horizontal lines.
Distortion is visible on the "bad" part of the CRT, but that's with any
kind of signal.

Regards.
Frank IZ8DWF
From: frank on 5 Oct 2009 11:35
Hi all,
I had time to investigate further the problem on this scope and I just
found out that the metallic shield around the CRT's neck is slightly
magnetized. I suppose this is a mu-metal tube to shield external
magnetic fields. I just don't know if a slight magnetizatization is
normal. The shield attracts a small blade in every place I tried, so
seems like a total magnetization.
Comments and hints are welcome.

Best regards
Frank IZ8DWF
From: Jim Yanik on 5 Oct 2009 14:05
frank <frank(a)ottone.venere.it> wrote in
news:4aca1238$0$694$5fc30a8(a)news.tiscali.it:

> Hi all,
> I had time to investigate further the problem on this scope and I just
> found out that the metallic shield around the CRT's neck is slightly
> magnetized. I suppose this is a mu-metal tube to shield external
> magnetic fields. I just don't know if a slight magnetizatization is
> normal. The shield attracts a small blade in every place I tried, so
> seems like a total magnetization.
> Comments and hints are welcome.
>
> Best regards
> Frank IZ8DWF
>


AFAIK,the CRT shield should not be magnetic.
Are you sure your blade is not magnetized?

try a TV degaussing coil to remove the magnetism from the shield.

--
Jim Yanik
jyanik
at
localnet
dot com
From: frank on 5 Oct 2009 14:23
Jim Yanik <jyanik(a)abuse.gov> wrote:
> frank <frank(a)ottone.venere.it> wrote in
> news:4aca1238$0$694$5fc30a8(a)news.tiscali.it:
>>
>
>
> AFAIK,the CRT shield should not be magnetic.
> Are you sure your blade is not magnetized?

you're right, I picked a magnetized blade :(
I checked with another one and this time I couldn't find any
magnetization on the shield.
So problem "solved".

>
> try a TV degaussing coil to remove the magnetism from the shield.

it has none, as far as I can tell at least. I read that a mu-metal
shield shouldn't magnetize at all.

Thanks for hint and best regards

Frank
From: Sjouke Burry on 5 Oct 2009 15:58
frank wrote:
> Hi all,
> I had time to investigate further the problem on this scope and I just
> found out that the metallic shield around the CRT's neck is slightly
> magnetized. I suppose this is a mu-metal tube to shield external
> magnetic fields. I just don't know if a slight magnetizatization is
> normal. The shield attracts a small blade in every place I tried, so
> seems like a total magnetization.
> Comments and hints are welcome.
>
> Best regards
> Frank IZ8DWF
Probably the blade is magnetized, it is made of hardened steel,
and can easily be magnitized.
The Mu metal attracts any magnet quite well, because it is so
soft(magnetically).
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