The Video Crudicon Tube?

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The Video Crudicon Tube?

Postby jjester6000 » Wed Mar 21, 2018 3:47 pm

Over the past few months I have been trying to design my own image pickup tube that I could realistically build with my limited resources. I have been so interested that I have nearly filled a whole notebook just with Cathode Ray Tube related sketches. I have experimented with making working crude electron accelerator tubes using a cheap vacuum pump and some glassware I picked up at my local crafts store. I have found that in order to make something permanent, I will need to properly heat up and melt the glass instead of just using a dremel and epoxy. So I have messed around with melting glass with my blow torch.

The tube I have designed is the product of months of sketching various types of CRT's.

20180320_143200.jpg
One of my final sketches that I scanned from my notebook.


I call it the "Crudicon Tube" because it is in fact crude.

It seems to be a cross between an original Iconoscope tube and a Vidicon tube. It works on a principle closer to the Vidicon yet uses the same offset electron gun design that the Iconoscope tube uses. This is because of my lack of a transparent conductor, which means that the selenium covered plate would have to be intercepted by the scanning beam on the same side that the image is focused onto it. Like a Vidicon, this tube outputs a video signal through photo-resistance differential; which means that the selenium changes its photo-conductive properties based on the amount of light hitting a particular area. Since this tube does not allow for charge storing, I expect performance to be pretty weak compared to other tubes. I used selenium as my photo-conductor since it was cheap, and I could easily melt a coat of it onto a small steel plate. The beam deflection will be done electromagnetically, not electrostatically, because I find electromagnets easier to work with then electrostatic plates.

I would like any feedback I could get for my design.

I am not an expert, so I may have overlooked something huge.
If life doesn't give you lemons - Grow Some DAMMIT!!!
jjester6000
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Re: The Video Crudicon Tube?

Postby Harry Dalek » Wed Mar 21, 2018 11:39 pm

It looks good like an Iconoscope design ,Troy on the Forum has made an iconoscope 626 line camera .
I wish you luck on building it ,you would have to get the electon gun right knowing you can focus it and scan it at those distances to the target .
If you can get it right in a CRT idea you could copy it for this ,that would test if you can focus the beam in the first place and can get enough vacuum .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Video Crudicon Tube?

Postby jjester6000 » Fri Mar 23, 2018 4:39 am

Here is a slightly updated design:

20180322_111508.jpg


I removed the accelerator grid, and added a transformer for a more complete circuit from the photocathode and anode. I plan for the tube to be rather small, a bit larger than a light bulb, so I think it will need to be a less focused beam to increase sensitivity. This may affect resolution, but the beam will have a larger radius of scanning at any given point.
If life doesn't give you lemons - Grow Some DAMMIT!!!
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Re: The Video Crudicon Tube?

Postby Harry Dalek » Fri Mar 23, 2018 10:52 am

It looks good i can see your going the cold cathode road .
Fanswoths first image tube was a cold cathode type so must be possible .
Small is good easier to get a higher vacuum ..if it were a PMT i know the output from the tube is very high but i know this is not the case on a vidicon .
I would ask Troy what is the case for the working iconoscope ..but i know he still had to use a preamp,so might be an idea to make one if signal is to low /
i still have a concern on the focusing perhaps a magnetic focusing coil as used on some early vidicons might be a goer for this too.
Are you going to use an old bulb for the housing they come larger A15 normal size then there is A19 21 23 ?
Also what line rate are you planning on using if it works out ?
Any case very interesting do show any build as a how to do when you get onto it .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Video Crudicon Tube?

Postby jjester6000 » Mon Jun 25, 2018 3:04 am

It has been a while since I last replied, so I will give you an update. I have turned my attention to designing my own Image Dissector Tube instead of the Crudiscope.

New Doc 2018-06-24_2.jpg


I have decided to wait on making a sealed prototype since I am not a very good glass blower. I also decided to use the photocathode from a cracked saticon tube I had because I havr not figured out any effective way to coat something with my selenium powder.

20180624_103654.jpg

20180624_103706.jpg


I have not been able to test it yet, but I will keep you updated over the next few days.
If life doesn't give you lemons - Grow Some DAMMIT!!!
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Re: The Video Crudicon Tube?

Postby jjester6000 » Mon Jun 25, 2018 11:33 am

I can't believe I am saying this, but it actually sort of worked!
(Until this happended)
20180624_191859.jpg

The photocathode heated up too much and just fell off, so I have no way of proving it. For about 30 seconds I found that it was responding to light vertically (I only had the vertical deflection coil hooked up at the time).
20180624_191859.jpg
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Re: The Video Crudicon Tube?

Postby Harry Dalek » Mon Jun 25, 2018 9:29 pm

Looking at the original Fanswoths drawing it looks to me like he had electrostatic deflection and magnetic focusing but no reason it could not be magnetic deflection as well but he used the other .
I too have played with cold cathode HV supply looking at yours need to explain the problems i found .
My first go at a cold cathode tube was similar but a mistake i made and i see you too have ....you should not have plastic to hold things together ,the thing might be called a cold cathode but there's a bit heat from a few thousand volts of electrons hitting that Anode if there's a low vacuum the sparking can cause more heat and as i found out fire inside the vacuum vessel and melting plastic !
I never got around to it yet but next design was to use glass tube to over come my past bad design ...such as in used in fuses take the fuse wire out it leaves a hole ..great just what you need for the Anode ..its to allow electrons to escape the other end can be the cathode and it should now cope with mistakes heating .
I would put a metal washer or similar if it fits around the anode end of the fuse .
You need to see that stream of electrons as a spot on the front screen of the vessel or its just Conjecture.
What are you using to try and make the vacuum ? i was using a old fridge compressor, but i have handy some large compressors that can be adjusted to suck instead of blow .
You will notice the difference in results when you get closer to a vacuum no sparking .
My advice playing around with a Vidicon would be ,first make a camera with a working tube of some sort that you know the electronics for a camera work then you have a test bed to test the wanted image tube .
Good luck its one of those things like we all have to do master different skills for a working end result might fail a few times but never know if you don't give up ..i admire your work keep at it i would love to see you get it working .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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