Re: 454, Amplitude Decline


J. Hemetsberger
 

Bob, thank you for your help.
Good idea, I didn't think of a constant magnetic field.
The instrument is definitely in its original condition and foreign bodies would not remain unseen. Do you think the mu-metal shield itself could have been magnetized?
However, I tried to influence the beam with a stack of permanent magnets (neodymium), but the deflection achieved was rather small.
Johann

-----Ursprüngliche Nachricht-----
Von: TekScopes@groups.io [mailto:TekScopes@groups.io] Im Auftrag von Bob Albert via Groups.Io
Gesendet: Mittwoch, 11. März 2020 21:05
An: tekscopes@groups.io; TekScopes@groups.io
Betreff: Re: [TekScopes] 454, Amplitude Decline

Perhaps some stray magnetic material has found its way into the unit. Maybe degaussing would help.
Bob

On Wednesday, March 11, 2020, 12:15:49 PM PDT, J. Hemetsberger <attergau@...> wrote:

Hi Tek group members!

I am a member of the hp group for years, but recently I registered at
TekScopes too. During the last year I repaired two 465's and now I have a
454 on the bench. Trigger and Vertical Switching are working again, but
there is a slight decline in the amplitude from left to right. It is not a
barrel distortion, because it is not symmetric to the vertical center. From
my understanding it has to do with the tube geometry but not with the
Vertical Output Amplifier because the effect is completely independent of
the time base setting.

A strait line (vertically centered & no signal applied) proceeds absolutely
along the horizontal grid center, but if shifted to the top the line bows
down by about 1/10 (to 2/10) Div. Inverse effect appears if the line is
shifted to the bottom, then it bows up.

Certainly the effect could be explained by vertical deflector plates
diverging from left to right due a strong mechanical shock, but that seems
unlikely to me.

The effect is rather weak but still a bit annoying. Unfortunately I did not
find anything suitable in the Service Manual.

Perhaps the deficiency could be fixed by adjustment. Thanks for any
suggestions.

Johann

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