Trying to make a vision IF and Detector - fun!

[AdrianPH]

Hi Trevor

I do little else, from being a radio engineer from Bench to systems, I enjoyed working on electronics both at home and work. When work became little more than computers and health and safety, ( I was also H&S Manager) I missed the fun side of it. So with lockdown's and little else to do I can literally spend hours a day at it now I stopped work a few years early.

I do have to give it a few days break every now and then.

By the way with you mentioning the MW6-2 reminded me, I have one you, or, anyone can have. The heater seems OK well resistance there anyway. There is some darkening of the screen a bit where I imagine it scanned the screen, but worse there are some areas of the screen that appear to have gone, possibly burnt away!?

I was thinking it may be of use to someone playing rather then mess with a good tube. It may not work I have no idea, as I can not run it.

If there is any interest I will try and take a picture of the front of the tube and put it in this thread .

The DG7-5 is now fitted looking a bit better focus etc, need a bit more height in the time base signals.

Adrian

[AdrianPH]

OK last post before sleep, have got the Image size better, with the DG7-5.
   

Here is a question for the thinkers, Please let me know where I am going wrong.
The spec of the DG7-5 says line size is 0.7mm, I would say that is the worst, and it could be better.

If the line timebase is 98.8uS long and the line blanking was 17.5uS then we have 81.3uS per line of video. 

If the maximum video bandwidth visible on the CRT is limited by the dot size then the fastest video would be with a dot first on and then off, with these two levels being spaced by the dot size. 
With each dot at 0.7mm then one cycle would be 1.4mm.  With a visual line width of only 60mm on the screen which equates to the 81.3 uS.  Then 1.4mm would equate to (1.4/60) x 81.3 uS  = 1.897 uS in time period which is a frequency of 527148 Hz.  If I can see the 1 MHz grating does that mean the dot size is around 0.37mm at least, or am I thinking to digitally?

Adrian

[peter scott]

The screen width is 67mm so with a 0.7mm spot you can resolve 95 points which in terms of grating lines is half that say 47 white and 47 black. The test card doesn't fill the full width of the screen. Let's say 90% so you can resolve 42 cycles in 81uS or 522kHz. If you can resolve the 1MHz bars then it suggests a spot size of about 0.35mm.

I didn't look at you working but I'd say we agree.

Peter

[AdrianPH]

OK thank you Peter, I was sure that my IF bandwidth was better than 1 MHz, but wondered for a while why I could not see better then the 1 MHz grating. I guess one can have less than 1 dot off, but not less than a dot on.
It then occurred to me about the size. The tube having a single focusing grid and lowish final anode, I was wondering if this was the best or should I be seeing better. I will try and take a picture and post it later I need to dig out my tripod for the camera.

Adrian

[AdrianPH]

OK two images the first relevant to the thread is a close up I have tried to take the best I can with my camera.
   

The second of the MW6/2 CRT I mentioned, I am assuming the marks are screen burn.
   

Adrian

[peter scott]

Your test card image is almost certainly being restricted by the (lack of) CRT focus and not by the spot size limitation.

Peter

[AdrianPH]

The focus pot goes through focus and out again the other side, what I am not sure about is my camera capturing it, it is fully auto I can not do a manual focus.

I will add a magnifying lens see if that helps.

[peter scott]

Your camera is resolving something at the periphery rather better the screen image.

   

Peter

[AdrianPH]

I am not getting notifications from the site!That was the receding edge of the glass, I think the camera was focusing in the glass face, or edge.

Most of my magnifying lenses are scratched though use in the garage or generally being stored in the drawer, I have found a small unit on one of the 3rd Hands and took this shot, AF illuminator switched off.
   

I think for the time being I will just be happy I have something viewable.

If I go to bigger electrostatic tubes I am going to have to up the EHT and if keeping the anode of the video valve feeding the grid will have to have very high voltage caps also going to the deflection plates to the timebase output.

There are only three alternatives that come to mind.
1)  Go negative HT and figure a way of dc restoration of the video down at something line - 1K2 Volts.
2)  Try to go magnetic deflection which with these Radar CRTs I have would be interesting trying to make some scan coils and sort out the circuit.
3)  Leave it as it is and call the exercise complete.


Adrian

[Murphyv310]

The MW6 - 2 has suffered either a frame or line collapse at some time and the protection wasn't quite fast enough.
The staining is normal with these after a few years use. It still will be very bright. They can run at 5 kv and still give pin sharp focus and good brightness. Scan requirements at 5kv can be driven by a few milli Watts.