Date   

Re: TV on a 7000 Scope - impossible on any other lab scope

PA4TIM
 

That is a great video. How do you do that. I found out the film itself also on youtube and seems to be is original clip from that song. So he feeds the video signal ( composite ? ) to the scope. Coult be a job for a raspberry pi.

Fred PA4TIM

Op 5 jun. 2013 om 12:10 heeft "John S" <John@...> het volgende geschreven:

 

I guess you may have already seen this, but it's one of my all-time favourites. (Good music as well).

http://www.youtube.com/watch?v=6Ac1G_5N73g

John

--- In TekScopes@..., "Dennis Tillman" wrote:
>
> There is a low power analog TV station still transmitting in Portland around
> 80MHz. Over the weekend a physics professor at Portland State University
> showed me his contribution to the list of impossible things only a 7000
> scope can do. He displayed the image from the TV station right off the air
> onto the CRT. He did it on a 7834 (storage was off) using a 7B70 and a 7B92
> in the outermost slots to generate a raster, and a 7L12 tuned to 80MHz to
> lock onto the TV station's signal. A simple telescoping whip antenna was all
> he used. Attached is a photo I took of the CRT of the 7834.
>
>
>
> When I got home to Seattle I could not find any analog stations still
> transmitting in our area so I had to figure out a quick way to make my own
> TV station. The picture I took duplicates the professor's work but with much
> poorer results since I was using a cheap wireless camera a substitute for
> the low power Portland TV station. Attached is an image I took of the QSL
> card from one of my ham radio friends - K7PJT. Contrast is poor due to the
> signal from the wireless camera but his call letters are clearly visible.
> The image was flipped and rotated to make it more readable so the on-screen
> readout appears sideways and backwards.
>
>
>
> Dennis
>


Re: Impossible Photo except on a 7000 scope

Mark Wendt <mark.wendt@...>
 

Yeah, Don mentioned that too. See my previous post on Ebay's lousy search. ;-)

Mark

On 06/05/2013 08:09 AM, Dave Daniel wrote:
Thanks.

Those are 7D20s, not 7J20s.

DaveD

On 6/5/2013 5:54 AM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD
Dave,

Ebay item #'s 360442801904, 390586622614, and 130922343379.

Mark


Re: Impossible Photo except on a 7000 scope

Mark Wendt <mark.wendt@...>
 

Well, that's very strange. I didn't look that close at the listings, but those were what turned up on a search for "Tektronix 7J20". Looks like Ebay's search has gotten even worse than what we discussed previously.

Mark

On 06/05/2013 07:58 AM, Don Black wrote:
Sadly, re-read the type. They are all 7D20s.

Don Black.

On 05-Jun-13 9:54 PM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD
Dave,

Ebay item #'s 360442801904, 390586622614, and 130922343379.

Mark


Re: Impossible Photo except on a 7000 scope

Dave Daniel
 

Thanks.

Those are 7D20s, not 7J20s.

DaveD

On 6/5/2013 5:54 AM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD
Dave,

Ebay item #'s 360442801904, 390586622614, and 130922343379.

Mark


------------------------------------

Yahoo! Groups Links



Re: Impossible Photo except on a 7000 scope

Don Black <donald_black@...>
 

Sadly, re-read the type. They are all 7D20s.

Don Black.

On 05-Jun-13 9:54 PM, Mark Wendt wrote:
On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD
Dave,

Ebay item #'s 360442801904, 390586622614, and 130922343379.

Mark


------------------------------------

Yahoo! Groups Links





Re: Impossible Photo except on a 7000 scope

Mark Wendt <mark.wendt@...>
 

On 06/05/2013 07:50 AM, Dave Daniel wrote:
I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD
Dave,

Ebay item #'s 360442801904, 390586622614, and 130922343379.

Mark


Re: Impossible Photo except on a 7000 scope

Dave Daniel
 

I see three 7D20s, but no 7J20s.

Can you post the listing URLs for the 7J20s?

Thanks
DaveD

On 6/5/2013 3:33 AM, Mark Wendt wrote:
On 06/04/2013 07:51 PM, Dennis Tillman wrote:
Hi Larry,
Best estimate is ~40 were actually built. I know of 6 that are in use or at
least in safe hands. Since they are so valuable and since there are so few I
try to keep in touch with the others that have them and share resources. I
recently discovered that an ExTek friend of mine for many years was directly
involved in their design and marketing.

Since the 7J20 is so unusual it is of interest to very few people so I don't
often mention it. Such was the case with my friend. Quite by accident I saw
he had the 7J20 manual and that is when I discovered his connection to it.

They are a brilliant use of CRTs and scan converters. There are very few
other instruments that can do what a 7J20 does and the prices for those
were/are 10x to 20x the price of the 7J20.

Dennis
Dennis,

Your timing, as usual, is impeccable. There are currently three 7J20's
up for auction on Ebay right not. ;-)

Mark


------------------------------------

Yahoo! Groups Links



Re: TV on a 7000 Scope - impossible on any other lab scope

John Sykes
 

I guess you may have already seen this, but it's one of my all-time favourites. (Good music as well).

http://www.youtube.com/watch?v=6Ac1G_5N73g

John

--- In TekScopes@yahoogroups.com, "Dennis Tillman" <dennis@...> wrote:

There is a low power analog TV station still transmitting in Portland around
80MHz. Over the weekend a physics professor at Portland State University
showed me his contribution to the list of impossible things only a 7000
scope can do. He displayed the image from the TV station right off the air
onto the CRT. He did it on a 7834 (storage was off) using a 7B70 and a 7B92
in the outermost slots to generate a raster, and a 7L12 tuned to 80MHz to
lock onto the TV station's signal. A simple telescoping whip antenna was all
he used. Attached is a photo I took of the CRT of the 7834.



When I got home to Seattle I could not find any analog stations still
transmitting in our area so I had to figure out a quick way to make my own
TV station. The picture I took duplicates the professor's work but with much
poorer results since I was using a cheap wireless camera a substitute for
the low power Portland TV station. Attached is an image I took of the QSL
card from one of my ham radio friends - K7PJT. Contrast is poor due to the
signal from the wireless camera but his call letters are clearly visible.
The image was flipped and rotated to make it more readable so the on-screen
readout appears sideways and backwards.



Dennis


Re: Impossible Photo except on a 7000 scope

Mark Wendt <mark.wendt@...>
 

On 06/04/2013 07:51 PM, Dennis Tillman wrote:
Hi Larry,
Best estimate is ~40 were actually built. I know of 6 that are in use or at
least in safe hands. Since they are so valuable and since there are so few I
try to keep in touch with the others that have them and share resources. I
recently discovered that an ExTek friend of mine for many years was directly
involved in their design and marketing.

Since the 7J20 is so unusual it is of interest to very few people so I don't
often mention it. Such was the case with my friend. Quite by accident I saw
he had the 7J20 manual and that is when I discovered his connection to it.

They are a brilliant use of CRTs and scan converters. There are very few
other instruments that can do what a 7J20 does and the prices for those
were/are 10x to 20x the price of the 7J20.

Dennis
Dennis,

Your timing, as usual, is impeccable. There are currently three 7J20's up for auction on Ebay right not. ;-)

Mark


Re: TV on a 7000 Scope - impossible on any other lab scope

Michael A. Terrell
 

The scopes I aw in TV shops in the mid '60 were free running, and very few would do 500 KHz. Several shop owners laughed when I bought a new Leader LBO-505 in the early '70s and told me scopes were a waste of money.


Dennis Tillman wrote:


Right. When I worked at a TV store in my youth we could tell when the
vertical sync tube was shot because the vertical would roll slowly at 60Hz.
Dennis

-----Original Message-----
From: Michael A. Terrell, Sent: Wednesday, June 05, 2013 12:36 AM

NTSC video is 59.94 Hz vertical and 15,734.34 Hz Horizontal. I used to watch
TV by feeding the video output of an old Polarad SA into an amber computer
monitor. Just for fun, I let it slowly sweep all the TV channels on the CATV
system and would ask the KNAs to explain what it was doing. ;-)


Re: TV on a 7000 Scope - impossible on any other lab scope

 

Right. When I worked at a TV store in my youth we could tell when the
vertical sync tube was shot because the vertical would roll slowly at 60Hz.
Dennis

-----Original Message-----
From: Michael A. Terrell, Sent: Wednesday, June 05, 2013 12:36 AM

NTSC video is 59.94 Hz vertical and 15,734.34 Hz Horizontal. I used to watch
TV by feeding the video output of an old Polarad SA into an amber computer
monitor. Just for fun, I let it slowly sweep all the TV channels on the CATV
system and would ask the KNAs to explain what it was doing. ;-)


Re: TV on a 7000 Scope - impossible on any other lab scope

Michael A. Terrell
 

Dennis Tillman wrote:

I don�t recall how the physics professor had his 7834 set up to display the Portland analog TV signal. I had to use a work around because I didn�t have a corresponding TV signal to use. As a result my setup was more complex and finicky than his.

The 7L12 resolution was set to 3MHz to correspond to the bandwidth of the video signal being transmitted. The Frequency Span/Div was set to 1KHz/Div which was the same as the sweep speed of the 7B70 in the left vertical slot. Both the 7B70 and the 7L12 were sync�d to 60Hz so they were sweeping synchronously. 60Hz is coincidentally very close to the actual vertical sync frequency of an analog TV signal. This coincidence is important. I do not know what the horizontal sync frequency is for the wireless camera I was using but I think it was close to 60Hz. The 7B92 was free running at 10uSec/Div in the far right horizontal slot. Up to this point I borrowed what I saw down in Portland. A lot of creative thinking was necessary on the part of someone to realize this could be done and to have figured out everything so far.

Where I had to improvise was by connecting the Vert Out signal from the 7L12 (on a front panel pin jack) to the Z axis input of the scope to modulate the intensity. Since the amplitude of the video signal is proportional to the brightness of the image (or inversely proportional, I forget) it modulates the brightness of the CRT showing the image of what is being transmitted by the wireless camera.

The final step was to capture a photograph of the CRT which I did with my HoodWink Scope camera.

Next time I am in Portland I will refine the experiment and narrow down all the variables until I am able to reproduce a better quality image. The important thing as far as I am concerned is this demonstrates yet another thing the 7000 series can do that no other scope is capable of.

Dennis

*From:*cheater00 .*Sent:* Tuesday, June 04, 2013 11:27 PM

Hi Dennis,
very fun indeed! How is the 7L12 used here? I haven't got any ideas!

Regarding using any scope in raster mode; this one was a head scratcher when I first tried raster mode..

In TVs we're used to the point scanning from left to right in rows, and then it scans more slowly top to bottom.

In scopes, vertical deflection has a much higher bandwidth than horizontal. So you should have the point scanning top to bottom, and then the rows should slowly progress left to right. So it's actually the natural way for raster mode to be: turned sideways.

Now what I want to see is someone using noise as the X and Y deflection, sampling something in this way, and then displaying it on the scope. Regeneration happens because you use the exact same noise signal. You don't need any sort of precise signal for carrying sampling information - it only needs to be accurate, not precise!

(accuracy means you can repeat measurements with the same results, precision means your measurements are close to the intended value).

So I want to see that, but it might need to wait until I've kludged together an SEM.

NTSC video is 59.94 Hz vertical and 15,734.34 Hz Horizontal. I used to watch TV by feeding the video output of an old Polarad SA into an amber computer monitor. Just for fun, I let it slowly sweep all the TV channels on the CATV system and would ask the KNAs to explain what it was doing. ;-)


Re: TV on a 7000 Scope - impossible on any other lab scope

 

I don’t recall how the physics professor had his 7834 set up to display the Portland analog TV signal. I had to use a work around because I didn’t have a corresponding TV signal to use. As a result my setup was more complex and finicky than his.

 

The 7L12 resolution was set to 3MHz to correspond to the bandwidth of the video signal being transmitted. The Frequency Span/Div was set to 1KHz/Div which was the same as the sweep speed of the 7B70 in the left vertical slot. Both the 7B70 and the 7L12  were sync’d to 60Hz so they were sweeping synchronously. 60Hz is coincidentally very close to the actual vertical sync frequency of an analog TV signal. This coincidence is important. I do not know what the horizontal sync frequency is for the wireless camera I was using but I think it was close to 60Hz. The 7B92 was free running at 10uSec/Div in the far right horizontal slot.  Up to this point I borrowed what I saw down in Portland. A lot of creative thinking was necessary on the part of someone to realize this could be done and to have figured out everything so far.  

 

Where I had to improvise was by connecting the Vert Out signal from the 7L12 (on a front panel pin jack) to the Z axis input of the scope to modulate the intensity. Since the amplitude of the video signal is proportional to the brightness of the image (or inversely proportional, I forget) it modulates the brightness of the CRT showing the image of what is being transmitted by the wireless camera.

 

The final step was to capture a photograph of the CRT which I did with my HoodWink Scope camera.

 

Next time I am in Portland I will refine the experiment and narrow down all the variables until I am able to reproduce a better quality image. The important thing as far as I am concerned is this demonstrates yet another thing the 7000 series can do that no other scope is capable of.

 

Dennis

 

From: cheater00 .Sent: Tuesday, June 04, 2013 11:27 PM

Hi Dennis,
very fun indeed! How is the 7L12 used here? I haven't got any ideas!

Regarding using any scope in raster mode; this one was a head scratcher when I first tried raster mode..

In TVs we're used to the point scanning from left to right in rows, and then it scans more slowly top to bottom.

In scopes, vertical deflection has a much higher bandwidth than horizontal. So you should have the point scanning top to bottom, and then the rows should slowly progress left to right. So it's actually the natural way for raster mode to be: turned sideways.

 

Now what I want to see is someone using noise as the X and Y deflection, sampling something in this way, and then displaying it on the scope. Regeneration happens because you use the exact same noise signal. You don't need any sort of precise signal for carrying sampling information - it only needs to be accurate, not precise!

(accuracy means you can repeat measurements with the same results, precision means your measurements are close to the intended value).

So I want to see that, but it might need to wait until I've kludged together an SEM.

Cheers,
D.

 

On Wed, Jun 5, 2013 at 12:56 AM, Dennis Tillman <dennis@...> wrote:

[Attachment(s) from Dennis Tillman included below]

There is a low power analog TV station still transmitting in Portland around 80MHz. Over the weekend a physics professor at Portland State University showed me his contribution to the list of impossible things only a 7000 scope can do. He displayed the image from the TV station right off the air onto the CRT. He did it on a 7834 (storage was off) using a 7B70 and a 7B92 in the outermost slots to generate a raster, and a 7L12 tuned to 80MHz to lock onto the TV station’s signal. A simple telescoping whip antenna was all he used. Attached is a photo I took of the CRT of the 7834.

 When I got home to Seattle I could not find any analog stations still transmitting in our area so I had to figure out a quick way to make my own TV station. The picture I took duplicates the professor’s work but with much poorer results since I was using a cheap wireless camera a substitute for the low power Portland TV station. Attached is an image I took of the QSL card from one of my ham radio friends – K7PJT. Contrast is poor due to the signal from the wireless camera but his call letters are clearly visible. The image was flipped and rotated to make it more readable so the on-screen readout appears sideways and backwards.

Dennis

Attachment(s) from Dennis Tillman

2 of 2 Photo(s)

,_._,___


Re: TV on a 7000 Scope - impossible on any other lab scope [2 Attachments]

 

Hi Dennis,
very fun indeed! How is the 7L12 used here? I haven't got any ideas!

Regarding using any scope in raster mode; this one was a head scratcher when I first tried raster mode..
In TVs we're used to the point scanning from left to right in rows, and then it scans more slowly top to bottom.

In scopes, vertical deflection has a much higher bandwidth than horizontal. So you should have the point scanning top to bottom, and then the rows should slowly progress left to right. So it's actually the natural way for raster mode to be: turned sideways.

Now what I want to see is someone using noise as the X and Y deflection, sampling something in this way, and then displaying it on the scope. Regeneration happens because you use the exact same noise signal. You don't need any sort of precise signal for carrying sampling information - it only needs to be accurate, not precise!

(accuracy means you can repeat measurements with the same results, precision means your measurements are close to the intended value).

So I want to see that, but it might need to wait until I've kludged together an SEM.

Cheers,
D.


On Wed, Jun 5, 2013 at 12:56 AM, Dennis Tillman <dennis@...> wrote:
[Attachment(s) from Dennis Tillman included below]

There is a low power analog TV station still transmitting in Portland around 80MHz. Over the weekend a physics professor at Portland State University showed me his contribution to the list of impossible things only a 7000 scope can do. He displayed the image from the TV station right off the air onto the CRT. He did it on a 7834 (storage was off) using a 7B70 and a 7B92 in the outermost slots to generate a raster, and a 7L12 tuned to 80MHz to lock onto the TV station’s signal. A simple telescoping whip antenna was all he used. Attached is a photo I took of the CRT of the 7834.

 

When I got home to Seattle I could not find any analog stations still transmitting in our area so I had to figure out a quick way to make my own TV station. The picture I took duplicates the professor’s work but with much poorer results since I was using a cheap wireless camera a substitute for the low power Portland TV station. Attached is an image I took of the QSL card from one of my ham radio friends – K7PJT. Contrast is poor due to the signal from the wireless camera but his call letters are clearly visible. The image was flipped and rotated to make it more readable so the on-screen readout appears sideways and backwards.

 

Dennis


Attachment(s) from Dennis Tillman

2 of 2 Photo(s)



Re: Explanation of the 7D20 "dip" straight from the 7D20 Project Manager

 

Hi Dennis,


On Wed, Jun 5, 2013 at 12:17 AM, Dennis Tillman <dennis@ridesoft.com> wrote:
My understanding is that that isn't exactly true. An analog signal is
continuous. A physical sampler has to start and to end. The start and end
points are discontinuous. A Fourier transform can be performed on the analog
signal, but the Discrete Fourier Transform of the sampled signal will have
problems with the first and the last samples because they are discontinuous.
That is incorrect. The exact same problem exists in the
continuous-domain Fourier transform, and basically in any other thing
that assumes an unbounded continuous domain. This issue is called the
"boundary problem". It has nothing to do with there being discrete
points. It's about the fact that at some boundary (here, the start or
the end) on one side you have enough information to reason about
what's happening, and on the other side of that point you don't.

Notice I said "information". According to the Shannon-Nyquist Sampling
Theorem (which is true), the discrete-time signal contains exactly the
same information as the continuous-time signal, up to Fs/2. Since we
don't care about what's above Fs/2, that's *exactly* what we want.
Discrete and continuous Fourier transforms yield exactly the same
results, but to compare you'd have to do a lot of pencil-and-paper
computation, so I'm not going to be able to show you something
conclusive.

The Sampling Theorem has very big weaknesses. For one thing, it
assumes an infinitely-long oversampling filter during regeneration. Or
more generally, when going from digital back to analog, it says it's
*possible* to reconstruct the signal, but doesn't say *how*.
Technology has shown it's absolutely impossible. In digital audio, you
could encounter this waveform (assume 1-bit sampling depth):
1111111111111111111111111111101111111111111111111111111111111

What does it look like? Well, according to the Sampling Theorem, it's
a sinewave which has had about 50 cycles during that span of time. To
arrive at this conclusion, you have to analyze a long chunk of digital
signal to even have the information needed to do it. That's because
future samples in a digital signal may change your interpretation of
the current sample you're interested in, and it's a major weakness of
the Sampling Theorem. In fact, the closer the frequency you're trying
to convey is to Fs/2, the more data you need to interpret it correctly
and reconstruct it in analog - to have full sampling capability up to
Fs/2 you have to make an infinitely-long oversampling filter, which is
impossible.

This non-determinism of analog waveforms produced according to the
Sampling Theorem is just one weakness. Another (perhaps linked, I
don't know..) is how badly it degrades.

In analog, and this is especially applicable in audio, you have the
following main forms of degradation:
1. noise. Noise is usually distributed in some uniform way and it just
means the signal is a bit less clear. Noise is extremely easy to
ignore, our minds are well trained for ignoring constant partials in
signals. If you don't trust me, try this experiment that will use an
optical signal. You're staring at a monitor right now. Is it dirty? Is
the backlight equally bright everywhere? Our eyes normally don't track
objects on the screen which helps hide this. Open up a new Notepad (it
has a white background) and maximize it. Then open a second one, and
make the window tiny, one inch across. Now move that new window while
the first one is in the background creating a white field of light.
While moving the smaller window, *track it with your eyes*. The object
needs to be this big, the mouse cursor itself wouldn't work, it's too
small. If you succeed at tracking the smaller window with your eyes
while it's moving, you should see all the dirt you've been staring at
for months without even knowing it's there.
2. non-linearity. This creates *harmonic* distortion which means that
even the error is in some way related to the input signal. In music,
it means the erroneous part of the signal is *musically related* to
the original signal, therefore musically pleasing. Don't trust me
distortion is musical? Ask Jimmy Hendrix.

In digital, you have however the following main forms of degradation:
1. quantization noise. It depends on the *level* of the signal and on
how many times it crosses a specific boundary. This is also called
"bit crushing". The error signal is a high-frequency "zipper" tone
that's difficult to ignore. If you want an example, find a wood-grain
table and slide your finger nail across it. You'll hear a zip. This
happens in exactly the same way as quantization: a specific signal (in
this case, the position of your finger in space) repeatedly crosses
sampling boundaries. If you use something that's more finely-grained,
like a very fine plastic-top office desk, the zipper noise becomes
less audible because there are more, smaller, finer "steps" in the
grain. If you use glass there's nothing because it's so fine. Now
here's the kicker: the best DACs in the world are unable to create
steps so fine that we are unable to hear them. A lot of analog
filtering has to happen for quantization noise to be removed
2. Aliasing. This one's absolutely terrible. The error signal's
frequency content is in no way musically related to the desired
signal. In fact, as your melody progresses, this one plays *against
you*. It's like having a drunken monkey sit beside you on the piano,
and it bashes keys exactly when you press keys.

I currently don't know of anything that could alleviate those issues.
There's no other way of digitally representing a signal sampled from
the real world that I know of which doesn't have those problems. I
have heard of mip-mapped sampling, but I haven't tried it yet and I
don't know whether it helps, in theory there are some things it could
be better at.

Just my 2 euro-cents.

D.

In certain cases the discontinuity can be minimized, for example if the
waveform being sampled is periodic and if by coincidence or design exactly
one or N (where N is an integer) periods is sampled then both the Fourier
transform and the Discrete Fourier Transform will yield the same results.

Beyond this point I suggest you discuss this in greater depth with someone
who does sampling for a living. I am satisfied that we have put to rest the
myth about "dip" in the 7D20. My focus is back to impossible things only a
7000 scope can do. See the latest photos I will publish in a few minutes.

Dennis

-----Original Message-----
From: cheater00. Sent: Tuesday, June 04, 2013 11:58 AM

<snip>

in a physical sampler (ideally) conversion from continuous to discrete time
and back gives you a flat frequency response up to Fs/2.



------------------------------------

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scanned: 5T3 Field Training

sipespresso <sipespresso@...>
 


Re: Impossible Photo except on a 7000 scope

Don Black <donald_black@...>
 

I meant a scan of the manual, from other postings I guess it's unobtainium platinum. Thanks for the explanations given.

Don Black.

On 05-Jun-13 11:41 AM, Don Black wrote:
 

They're great photos. I've never heard of the 7J20 before, does anyone know if a pdf scan is available n the Internet please. I'd like to have a look and see what it can do.

Don Black.

On 05-Jun-13 8:31 AM, Dennis Tillman wrote:

 

Attached is a image made from stitching two photographs together of the atomic spectrum of a Mercury Vapor Lamp. The spectrum runs from 400nm (Ultraviolet) on the far left to 1200nm (Infrared) on the far right.

This was taken with a 7J20 Rapid Scan Spectrometer plugin. The 7J20 is capable of capturing an entire 400nm spectral range in one instant or of resolving lines separated by less than half a  nanometer.

 

Also shown is the famous Sodium D2 doublet from a High Pressure (HP) Sodium Vapor Lamp. Unfortunately the presence of mercury in the HP Sodium lamp contaminates the doublet which would be different in amplitude in a true sodium spectra.   




Re: 7A26 Shuts down 7623A

Rob <rgwood@...>
 

I think the high points have all been hit. Look in the 7A26 manual and measure the + and – 15 and 50 V voltage supply pins to ground. You should see capacitance. i.e. starts at some ohms and builds higher  or discharges and builds when reversing leads.  If you only see resistance especially if it is low  suspect shorted tants.

 

I agree with the post on not just replacing caps and hoping it fixes the problem. However once I have trouble shot and found the correct capacitor/s I usually do go ahead and recap the plug-in. The manual lists all the electrolytic capacitors so it is pretty straight forward to do.. Great care should be taken if replacing any on the ‘front end’ because some of the cards are made of a type of rubber (for lack of better wording). I do often skip replacing these as a result. Chemicals (even alcohol) can cause issues there as well. The manual has adequate warnings just need to heed them.  

 

Another slight possibility is that the card slot in the mainframe is causing the problem. Make sure both sides have the white covers installed. These tend to keep everything aligned properly and if missing major headaches can arise.

 

Finally, and my biggest reason for posting because you already have been given great advice. If you are indeed going to just list them for parts. It might be wise to let it be known here 1st. I and/or others here would likely offer you reasonable amount and save you the listing fees, etc. more than likely allowing for a win-win situation.   I think however you will quickly repair these two with the help you will receive here. It is a great community.

 

Thanks as always for the bandwidth.

Rob


Re: Impossible Photo except on a 7000 scope [2 Attachments]

Don Black <donald_black@...>
 

They're great photos. I've never heard of the 7J20 before, does anyone know if a pdf scan is available n the Internet please. I'd like to have a look and see what it can do.

Don Black.

On 05-Jun-13 8:31 AM, Dennis Tillman wrote:
 

Attached is a image made from stitching two photographs together of the atomic spectrum of a Mercury Vapor Lamp. The spectrum runs from 400nm (Ultraviolet) on the far left to 1200nm (Infrared) on the far right.

This was taken with a 7J20 Rapid Scan Spectrometer plugin. The 7J20 is capable of capturing an entire 400nm spectral range in one instant or of resolving lines separated by less than half a  nanometer.

 

Also shown is the famous Sodium D2 doublet from a High Pressure (HP) Sodium Vapor Lamp. Unfortunately the presence of mercury in the HP Sodium lamp contaminates the doublet which would be different in amplitude in a true sodium spectra.   



Re: Impossible Photo except on a 7000 scope [2 Attachments]

teamlarryohio
 

Thanks! The ad with the DPO is great! I had a few of those cross my
bench back then, but not with 7J's in them.

I added the 1975 catalog which helped a bit. In any case,
it's a pretty incredible piece of work.
-ls-


"Dennis Tillman" <dennis@ridesoft.com> wrote:

This may help. It is all I have in electronic form.
I did not take the pictures. One of the other 7J20 owners did.
Dennis

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf
Of larrys@teamlarry.com
Sent: Tuesday, June 04, 2013 5:07 PM
To: TekScopes@yahoogroups.com
Subject: RE: [TekScopes] Impossible Photo except on a 7000 scope

Is there a writeup anywhere about how it does its magic? You're waking up
my curiosity :-) thanx,
-ls-


"Dennis Tillman" <dennis@ridesoft.com> wrote:
They are a brilliant use of CRTs and scan converters. There are very
few other instruments that can do what a 7J20 does and the prices for
those were/are 10x to 20x the price of the 7J20.


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