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Composite to XYZ tube converter, how to convert scope for Z?

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neazoi

neazoi

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Hi I would like to build the tube composite to XYZ converter presented on that page https://www.electronixandmore.com/projects/tvtoscope/index.html and combine it with a Heathkit SB-610 (schematic attached).
This scope does not have Z-input (intensity of trace).
I wonder if there is any way I can do a slight conversion to have the scope has a Z-input?
 

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  • sb610.pdf
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  • tvscope11.gif
    tvscope11.gif
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AC couple to the CRT cathode to modulate the brightness, the Z axis. HV caps
needed, consult manual for V readings of the cathode.


Regards, Dana.
 

    neazoi

    neazoi

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What are you trying to achieve with this?
Be aware that the SB-610 is basically a very simple oscilloscope with almost no functions except to show voltage vs. time on a small CRT. The 'tvscope' is to display composite video on a scope screen and as such has frequency selective sync pulse extraction. If you want to display an analog TV picture (if you can find one these days) the modification will work but for any other purpose it will be useless.

Brian.
 

    neazoi

    neazoi

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betwixt said:
What are you trying to achieve with this?
Be aware that the SB-610 is basically a very simple oscilloscope with almost no functions except to show voltage vs. time on a small CRT. The 'tvscope' is to display composite video on a scope screen and as such has frequency selective sync pulse extraction. If you want to display an analog TV picture (if you can find one these days) the modification will work but for any other purpose it will be useless.

Brian.
Click to expand...
Yes Brian. I am trying to display on that scope an analogue TV picture. The composite source is a Tono (Drake) theta 7000 "communications computer", which outputs a B&W (not grayscale) composite.
The scope is tube based and it is used in a retro station setup. It would be nice to build something to match the tube technology of the station, that displays the output of the keyboard to the scope, instead of using a cheap Chinese modern analogue TV.

There is an intensity potentiometer, so a way to fine-vary this electronically is needed I guess?
 

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  • comms.jpg
    comms.jpg
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"slight conversion" - no way!
The problem is the SB-610 sweep generator (V3a and V3b) has to be increased in frequency from one or two KHZ to a fixed 15.734KHz (or 15.625 if it was designed for PAL system TVs) and also synchronized to the incoming composite video. You would have to generate your own vertical scan signal at either 60Hz or 50Hz.

The incoming video would need its sync stripping out and fed to the sweep generators and you would also have to raise the video signal level to an amplitude of (a guess) 50V peak to peak with a bandwidth of at least 4MHz and preferably 6MHz or more. Then you have to modulate the CRT intensity with that video. Note that the CRT cathode is at approximately -1.3KV so coupling to it wouldn't be easy and you can't simply connect to the intensity voltage because R506 and the capacitance of C503/C504 and the power transformer will kill all high frequencies.

So it isn't impossible but I would say impractical. It would probably be easier to convert the TV into a signal monitor than the other way around!

Brian.
 

    neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
betwixt said:
"slight conversion" - no way!
The problem is the SB-610 sweep generator (V3a and V3b) has to be increased in frequency from one or two KHZ to a fixed 15.734KHz (or 15.625 if it was designed for PAL system TVs) and also synchronized to the incoming composite video. You would have to generate your own vertical scan signal at either 60Hz or 50Hz.

The incoming video would need its sync stripping out and fed to the sweep generators and you would also have to raise the video signal level to an amplitude of (a guess) 50V peak to peak with a bandwidth of at least 4MHz and preferably 6MHz or more. Then you have to modulate the CRT intensity with that video. Note that the CRT cathode is at approximately -1.3KV so coupling to it wouldn't be easy and you can't simply connect to the intensity voltage because R506 and the capacitance of C503/C504 and the power transformer will kill all high frequencies.

So it isn't impossible but I would say impractical. It would probably be easier to convert the TV into a signal monitor than the other way around!

Brian.
Click to expand...
Ok Brian I understood these problems you mention and indeed it seems much more difficult and scope-ruining than I imagined. I am not going to do it. Thank you for pointing me to the right direction.
73
 

Some thoughts :

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There is nothing wrong with your television set. Do not attempt to adjust the picture. Where would we be if we listened to advice like that? [Eric] writes that with a fairly simple circuit, he&#821…
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Regards, Dana.
 

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