5AHP7A Vintage SSTV The Deep image

[Harry Dalek]

Harry, this is a P7 phosfor, which is a two layer phosfor. The most inner layer gives a blue light, you can see that if you look from the back side into the CRT. The front layer is a long decay yellow phosfor. It is illuminated by the blue light and then gives a yellow after glow of several seconds.

If you swipe with a magnet around the neck of the tube you can deflect the spot and you will see that it leaves a yellow trace oon the screen. Normally in SSTV practice you place a yellow colour filter (yellow plexiglass) in front of the screen, which will be untransparent for the blue illumination spot and you see only the yellow after glow. I placed then a circular polarized Polaroid filter in front of all. This gives a better contrast as it attenuates the surrounding light twice and the light from the screen only once. That makes the screen much darker.

Ok thanks Klass i didn't know that ...interesting i will try a filter if i can come across something when i get it going .

[Klaas Robers]

There is a lot of this yellow plexiglass. In the IC technology a photo resist laquer is used that hardens (polymerizes) under blue light. To prevent it from hardening under the room light, yellow light is used and all windows are fitted with this yellow plexiglass. These areas are dust free and in yellow light. Workers there have extra overall and a cap on their head to prevent particles from their clothes, hair and body to escape and spoil the dust free environment. At our Philips research labs we have a rather large "yellow room", which is used by workers from ASML, the company that makes large machines for the chip industry world wide. The ASML company is 20 minutes bicycling from our labs. Yes it was a spin off from Philips Research and they moved not so far. There are close cooperations. This yellow room is still a remain from the time before.

So the plexiglass in yelow is quite common.

[Harry Dalek]

There is a lot of this yellow plexiglass. In the IC technology a photo resist laquer is used that hardens (polymerizes) under blue light. To prevent it from hardening under the room light, yellow light is used and all windows are fitted with this yellow plexiglass. These areas are dust free and in yellow light. Workers there have extra overall and a cap on their head to prevent particles from their clothes, hair and body to escape and spoil the dust free environment. At our Philips research labs we have a rather large "yellow room", which is used by workers from ASML, the company that makes large machines for the chip industry world wide. The ASML company is 20 minutes bicycling from our labs. Yes it was a spin off from Philips Research and they moved not so far. There are close cooperations. This yellow room is still a remain from the time before.

So the plexiglass in yelow is quite common.

I have seen the clear stuff for sale but yellow i am not sure .have to keep an eye out.
Does it have to be acrylic i have seen thicker plastic folders that are yellow you can cut up...if its more the colour needed.

Not much left from my first SSTV but a bit of work at the time here ,it was a bit of a mix so only used parts of these 2 circuits and some of my own ideas never did draw up a full schematic so that part is lost to me ,i know both deflection circuits worked but i know i went with the 741 version.

[AncientBrit]

Morning Harry,

Regarding optical filters for the CRT I have been experimenting producing these using a colour ink jet printer.
I have had some success in printing a graticule and 'colour wash' on clear film intended for use in ink jet printers.
I used AutoCAD and selected the filter colour by trial and error to suit the small green phosphor CRT I was using as a 'scope.
I'm sure any other 'paint' program would also be suitable.
The only down side is that the film has a slightly rough surface presumably to act as a key for the ink.

Cheers,

Graham

[Harry Dalek]

Morning Harry,

Regarding optical filters for the CRT I have been experimenting producing these using a colour ink jet printer.
I have had some success in printing a graticule and 'colour wash' on clear film intended for use in ink jet printers.
I used AutoCAD and selected the filter colour by trial and error to suit the small green phosphor CRT I was using as a 'scope.
I'm sure any other 'paint' program would also be suitable.
The only down side is that the film has a slightly rough surface presumably to act as a key for the ink.

Cheers,

Graham

HI Graham
Thats interesting i would never of thought of printing one out ! better not tell the wife why the ink levels are low !
I suppose it could work well with as you say some trial and error testing ...what was your interest in changing the colour of your scope trace ...i don't think i have heard of this being tried ...mixing green trace with the other filters makes me wonder about the colours you get ..a white trace scope would be useful for colour wheel nbtv experiments .

On the monitor i am putting together i found i have the SCRS the originals infact needed for the sawtooth oscillators circuit so i am putting that together ,made this in the past a few times so time to recycle and use whats in the junk box .

[AncientBrit]

Hi Harry,

Adding a coloured filter was purely to improve contrast ratio so the colour was chosen to match that of the phosphor.

In your case you would need to chose a filter to pass either the initial trace or the afterglow.

To get the density you might need to use two filters together.

Cheers,

Graham

[Harry Dalek]

Hi Harry,

Adding a coloured filter was purely to improve contrast ratio so the colour was chosen to match that of the phosphor.

In your case you would need to chose a filter to pass either the initial trace or the afterglow.

To get the density you might need to use two filters together.

Cheers,

Graham

OK Graham i see ,i am still aways for needing it but its good to know theres something i can try if i can't track something else down ...seems to easy not to try !
Going to test the sawtooth oscillators today .

[Harry Dalek]

Both sawtooth oscillators work which is good i will work on the second half driving the deflection coils next .
BTW i used bc547 for the bipolar tranies and c203b prx for the scr circuits not to fussy its always worked for me .

[Harry Dalek]

I finished the Transistor SSTV deflection circuit yesterday and today i hooked up the voltages to the CRT and fired it up .
Running again on a low EHT of 3000 volts here .
A quick test hooking up the deflection yoke and i have scanning but i think i have the horizontal and vertical on wiring on the yoke wrong way around ,i will swap the yoke coil around and see .
Oh well only took me 6 months to do a bit more
Still need a Sync Separator and test the beam modulation least its doing some thing now and i have something to work with .

[Klaas Robers]

Harry, because the scannings are running free, you should be able to adjust for a square scanning field. So reduce the horizontal scanning width and expand the vertical scanning heighth. They should be comparable, such that you get a square scanning field. Then adjust the horizontal sawtooth frequency to 16,6 Hz, that is 60 msec for one line, and the vertical scanning duration to 7,2 sec. Then at least your scanning is running at the correct speed. After you have done that synchronisation becomes much easier.

But first it is time to finish the video amplifier and connect that to the picture tube. Then at least you can see something from known SSTV signals and for implementing the synchronisation it is needed that you can see what happens. So the sync separator comes after the video chain working.

[Harry Dalek]

Harry, because the scannings are running free, you should be able to adjust for a square scanning field. So reduce the horizontal scanning width and expand the vertical scanning heighth. They should be comparable, such that you get a square scanning field. Then adjust the horizontal sawtooth frequency to 16,6 Hz, that is 60 msec for one line, and the vertical scanning duration to 7,2 sec. Then at least your scanning is running at the correct speed. After you have done that synchronisation becomes much easier.

But first it is time to finish the video amplifier and connect that to the picture tube. Then at least you can see something from known SSTV signals and for implementing the synchronisation it is needed that you can see what happens. So the sync separator comes after the video chain working.

Hi Klass i did try on my control trimmers .
I am going to have to look into whats up in the vertical and horizontal adjustment side such as the width control the horizontal has position control as i have slight width control to the line ...the vertical has a position control and width control but they are much less weaker than the horizontal side ...if i swap the deflection yoke coils visa versa the the horizontal is much smaller and the vertical is longer .
Just to make sure ...my horizontal as in the past posting is using the the 41 ohm coil and the vertical 15 ohm...i will try a few ideas to match the scan line length width to get the correct aspect ratio /
I have not made a sync circuit yet but i do have Steves working demodulator from 6 month back waiting to be used here...i have made the video amp circuit top circuit with a high voltage trany i had handy and with my tube focus and brightness wiring bottom schematic ...
I need to do as you suggest and get the scanning line widths ratio right right so i will work on that .
viewtopic.php?f=8&t=2080&start=60
i just found reducing the 5ohm resistor on the deflection coil circuit increased the vertical deflection by twice the amount ...i need to reduce the horizontal deflection still way to high for this .

[Klaas Robers]

Harry, I think 41 ohms is quite high.... But any way, both coils are composed of two two coils that can be circuited in series or parallel. Find out which coil is the coil that gived the too low deflection. If that is the 41 ohm coil-set, then I am almost sure that those coils are in series and are the 41 ohm one. Then try to circuit them in parallel.

But first use your oscilloscope to find out what the voltages are over the deflection coils. This cannot be more than the supply voltage that you have.

Succes!! Klaas

[Harry Dalek]

Harry, I think 41 ohms is quite high.... But any way, both coils are composed of two two coils that can be circuited in series or parallel. Find out which coil is the coil that gived the too low deflection. If that is the 41 ohm coil-set, then I am almost sure that those coils are in series and are the 41 ohm one. Then try to circuit them in parallel.

But first use your oscilloscope to find out what the voltages are over the deflection coils. This cannot be more than the supply voltage that you have.

Succes!! Klaas

Thanks klass for the information there i will have to take the deflection yoke off the crt and open up the plastic housing covering the yoke coil wiring to see ,i remember looking before i mounted it on the crt so i know i can get at it .

OK i will look at the voltages when its working the deflection amp is running on a dual 12 volt supply .

The horizontal when scope set on 5 volts per div is 10 volts the vertical on a volt per div looks to be 4 volts . on the gifs the first didn't come out well as i was trying to show the horizontal and vertical sawtooths and at same time of the dual scope not easy one a analog via a camera so i just put the vertical up to about 1 sec here instead of 7 or 8 ..any case the bottom line is the vertical showing .

Second gif is rge horizontal saw tooth at the deflection coil 41 ohm

The scanning looks like i have done something here .. the scanning line gone high on one end low on the other as the frame scans might have the coil connections wrong some thing else to look into .

[Klaas Robers]

harry, it looks as if there is cross talk from the horizontal scanning into the vertical scanning. The scanned field should be a square, at least a rectangular shape. But it is a trapezium. Strange.

But first make the horizontal scanning less, such that you can see the whole line, not only the center. I now cannot see what the line does at its ends. It might be possible that the two coils are not perpendicular to each other, which you can see at the ends of the scannings.

And look woth your oscilloscope on DC to the +12 and -12 supply voltages. they should be stable and you may not see any lowering and rising due to the horizontal and especially the vertical scannings.

[Harry Dalek]

harry, it looks as if there is cross talk from the horizontal scanning into the vertical scanning. The scanned field should be a square, at least a rectangular shape. But it is a trapezium. Strange.

But first make the horizontal scanning less, such that you can see the whole line, not only the center. I now cannot see what the line does at its ends. It might be possible that the two coils are not perpendicular to each other, which you can see at the ends of the scannings.

And look woth your oscilloscope on DC to the +12 and -12 supply voltages. they should be stable and you may not see any lowering and rising due to the horizontal and especially the vertical scannings.

Hi Klass
I can drop the horizontal with a resistor in series with the coil might be neater to drop the voltage to the deflection amp but this is nice and quick ....any case i can show all the line this way

Yes i have now checked the dc supply on the scope while its running its stable ...did notice its picking up inverter increasing the scope volts/div,but apart from that it looks fine no voltage change .
The 2nd gif is o volts positive 12 the negative 12 volts with increased volts/div you can see the inverter showing up on the power supply both rails .

To me dropping the horizontal to the deflection yoke i can still see the shape but a lot smaller ..i am not sure why but the vertical looks to match the drop i would of thought i would of got a longer scan aspect ratio wise .

The sawtooth is not as clean shape wise as my NBTV LM311 sawtooth circuits perhaps i should of went with those at sstv scanning frequencies.