开云体育

CRT has been replaced and all works fine. This particular 2215 has no regulator board. Is there any way to avoid damaging this new CRT? Would keeping a low grid bias make any difference?
Thanks guys.

On Thu, Jul 5, 2018 at 01:19 pm, lop pol wrote:

CRT has been replaced and all works fine. This particular 2215 has no
regulator board. Is there any way to avoid damaging this new CRT? Would
keeping a low grid bias make any difference?
Thanks guys.

Make sure it has been modded according to SUP3010:
/H?kan

Exactly what I was looking for. Thank you

Thanks a lot for this document Hakan, didn't know about this problem !

As it happens I just got a 2215 the other day, working on it as we speak... just checked, it's smack in the middle of the affected S/N range (mine is #20521), and it appears not to have been moded : no sticker at the back, and the transformer looks stock : still in revision -00 and the wire has not been unwound by one turn.

So my CRT / filament is cooked then, by now, after nearly 40 years of use... oh well... not much I can do about it, but at least if I find the trace too dim at fast sweep speeds (haven't checked specifically for that yet), I will know why and won't waste trying to "fix"/troubleshoot something that just can't be cured ! :-(


Vincent Trouilliez

So my CRT / filament is cooked then, by now, after nearly 40 years of use...
oh well... not much I can do about it, but at least if I find the trace too
dim at fast sweep speeds (haven't checked specifically for that yet), I will
know why and won't waste trying to "fix"/troubleshoot something that just
can't be cured ! :-(

At the time we had a simple procedure at our Field Office to determine
if the CRT should be replaced or not. I don't recall if it was an official procedure
or something we came up locally. We set the T/B to the fastest sweep speed with
X10 Magnifier, Hold Off to max, Auto Trig and no input signal. If the trace could
be seen with Intensity set to max , even just quite dim, the CRT was considered OK.

/H?kan

On Fri, Jul 6, 2018 at 11:08 am, zenith5106 wrote:

We set the T/B to the fastest sweep speed with
X10 Magnifier, Hold Off to max, Auto Trig and no input signal. If the trace
could be seen with Intensity set to max , even just quite dim, the CRT was
considered OK.

OK... just perform said test, here is the result :

/g/TekScopes/photo/62323/0?p=Name,,,20,1,0,0

I adjusted the ISO setting of the camera so that the brightness on the pic actually matches the brightness level that my eyes perceive.
That's under normal conditions : a couple fluorescent tubes above the bench for lightning, and me sitting right in front of the scope, at a close but reasonable distance, I mean I did glue my face to the screen...

Looks like an "acceptable" tube then ? I mean it's very difficult to see, and any dimmer than this, would make it invisible but... as you say, you can still see the trace.

Plus, if I turn the var hold-off to the min, brightness comes back to normal, the trace becomes perfectly visible, no effort needed whatsoever.

I will admit I don't really master the var hold-off feature, I am not sure I get why it impacts the brightness level.. but obviously it does. Will need to do some reading and experimenting ! ^^

Anyway, looks like my CRT is not worn out in the end, what do you say ? That's good ! :-)
I mean I have sooo many problems left to fix on this scope, I really didn't need yet another (costly ! ) problem on my list ! LOL


Regards,


Vincent Trouilliez

Thank you Hakan!
That is an excellent test that will probably work on other scopes to get an idea if the CRT is good.
Your contributions to Tekscopes are always good, and usually you are the only one on the planet that has the information you post.
tom jobe...

On 7/6/2018 12:25 PM, Vincent Trouilliez wrote:

Plus, if I turn the var hold-off to the min, brightness comes back to normal, the trace becomes perfectly visible, no effort needed whatsoever.
I will admit I don't really master the var hold-off feature, I am not sure I get why it impacts the brightness level.. but obviously it does. Will need to do some reading and experimenting ! ^^

The hold-off circuit introduces a delay between one sweep cycle and the next. Thus the longer the delay, the less often the sweeps occur, which affects the brightness. If the trace is bright with minimum hold-off, you should be in good shape.

If the trace goes dim with just a little hold-off, particularly at slow sweep rates, there may be a problem in the hold-off circuit.

John

On Fri, Jul 6, 2018 at 10:35 pm, John Kolb wrote:

The hold-off circuit introduces a delay between one sweep cycle and the next.
Thus the longer the delay, the less often the sweeps occur, which affects the
brightness. If the trace is bright with minimum hold-off, you should be in
good shape.

Thanks a lot John, in just a couple lines you managed to make it all limpid ! :-)

So looks like the Hold-off feature can be used to "select"/pick a particular event in a complex waveform. I now understand why someone advised me to fiddle with hold-off when I was trying to get a clear picture of the switched currents in the inverter of the SMSP of my 2232 scope, which I was fixing. There was a "current sense" resistor which was common to both windings, so I conveniently used it. Of course that meant that I would see the switched current of both windings on the same trace, "interleaved".

Without hold-off, the scope would trigger on both windings indistinctly, hence superimposing them on top of each other. Since the two currents did not have exactly the same amplitude, on the screen I would see a "double" waveform, as if the trace was unstable, which it was not then, just the two currents being "stacked" on one another. When I fiddled with hold-off I could get rid of the double waveform and "select" which of the two currents I wanted to see, and have only that one on the screen. Was great ! :-)

Sorry for the rambling/thinking out loud, but I like it so much when someone with just a few words can clarify something that's been obscure for so long ! ^^

Thanks :-)

Anyway, to get back on topic : looks like my CRT is not worn out, that's a big relief indeed...



Vincent Trouilliez

Hi H?kan,

That SUP is interesting. Do you have any other SUPs for other Tek gear? (I had a brief look on your website but wasn't able to find anything.)

Thanks, Brian.

That SUP is interesting. Do you have any other SUPs for other Tek gear?

Probably, but all on microfiche. What are you looking for ?
/H?kan

H?kan,

I'm not looking for anything specific, just looking to have them more publicly available, findable (Google / Bing), and searchable. My preferred route would either be to archive some sort of machine readable copies at or, as some documents already are, linked through to your website.

Is there an index of titles?

Regards, Brian.

Is there an index of titles?

Not in the microfiche that I'm aware of. If an instrument had a SUP, not the same a common mods,
it is included in the microfiche section concerning that specific instrument.

/H?kan