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Deflection ampilfiers

PostPosted: Tue Feb 21, 2017 6:29 pm
by Harry Dalek
HI Klass if you see this i changed the 470uf for 1nf on the vertical side this now gave a very thick line as in the animated gif's they look a little slowed down but to the eye it looks that thickness but the line is all white .

I left the horizontal cap as is for now ...is the oscillation the sinewave i see in the line the horizontal line the oscillation you have mentioned showing up if so interesting .

I dare say a change of value is called for unless theres something else you want to see tested .

Re: Deflection ampilfiers

PostPosted: Tue Feb 21, 2017 6:58 pm
by Andrew Davie
No need for animated GIFs! Video files should work. No file size limits!

Re: Deflection ampilfiers

PostPosted: Tue Feb 21, 2017 7:18 pm
by Klaas Robers
Harry, it is oscillating ! This is what you see when it is oscillating !

Now increase the value of the capacitor first in steps of 10 x. So make it 10 nF, then 100 nF and you will see that the oscillation stops, far before you reach 470 uF.

Then when this is at say 100 nF, go back in steps of 2, so 47n, 22n. As soon as you see the oscillation starting again, go one step of 2 x forward again. That is the optimal value, then you have the fastest non oscillating amplifier. And you will see that the cross-over distortion also disappeared.

To do this with the horizontal amplifier you need to have video on the screen. Then you run vertical white lines and you see the same effect that you see now, thick lines. And again do the trick with steps of 10 and then back with steps of 2. It is so nice that three steps of 2x equals to one step of 10 x. This is because 2^3 equals to 10..... almost.

Re: Deflection ampilfiers

PostPosted: Tue Feb 21, 2017 10:34 pm
by Harry Dalek
Andrew Davie wrote:No need for animated GIFs! Video files should work. No file size limits!


OH Andrew in this case the Gifs were very good as it dropped frames to show the sinewave so not so much what i saw but what its doing ,but i should of added the avi file as well .

OH i see a SSTV topic i am pleased ~!

Re: Deflection ampilfiers

PostPosted: Tue Feb 21, 2017 10:45 pm
by Harry Dalek
Klaas Robers wrote:Harry, it is oscillating ! This is what you see when it is oscillating !


Now i understand what you were asking me to do yes i see the horizontal scan line is oscillating good thing to show for i have never seen this before ,

Now increase the value of the capacitor first in steps of 10 x. So make it 10 nF, then 100 nF and you will see that the oscillation stops, far before you reach 470 uF.


OK will do !
i wish in this case and i should make one is a capacitor version of a resistor wheel that would come in handy for quick tests .

Then when this is at say 100 nF, go back in steps of 2, so 47n, 22n. As soon as you see the oscillation starting again, go one step of 2 x forward again. That is the optimal value, then you have the fastest non oscillating amplifier. And you will see that the cross-over distortion also disappeared.


OK i will get those capacitors and try your procedure ....

To do this with the horizontal amplifier you need to have video on the screen. Then you run vertical white lines and you see the same effect that you see now, thick lines. And again do the trick with steps of 10 and then back with steps of 2. It is so nice that three steps of 2x equals to one step of 10 x. This is because 2^3 equals to 10..... almost.


OK thats for later on i will work on the vertical till i can do that i was wondering about how to do the horizontal side ...Again thanks for the help Klaas !

Re: Deflection ampilfiers

PostPosted: Wed Feb 22, 2017 9:24 am
by gary
Andrew Davie wrote:No need for animated GIFs! Video files should work. No file size limits!


Hi Andrew, I suppose the advantage of a gif is you don't have to download the file, and then play it, to see it.

This would also be the case for videos if they could be embedded, is there anyway of doing that?

Re: Deflection ampilfiers

PostPosted: Wed Feb 22, 2017 5:49 pm
by Harry Dalek
Klaas Robers wrote:Harry, it is oscillating ! This is what you see when it is oscillating !

Now increase the value of the capacitor first in steps of 10 x. So make it 10 nF, then 100 nF and you will see that the oscillation stops, far before you reach 470 uF.

Then when this is at say 100 nF, go back in steps of 2, so 47n, 22n. As soon as you see the oscillation starting again, go one step of 2 x forward again. That is the optimal value, then you have the fastest non oscillating amplifier. And you will see that the cross-over distortion also disappeared.

To do this with the horizontal amplifier you need to have video on the screen. Then you run vertical white lines and you see the same effect that you see now, thick lines. And again do the trick with steps of 10 and then back with steps of 2. It is so nice that three steps of 2x equals to one step of 10 x. This is because 2^3 equals to 10..... almost.



HI Klass
I started off with a 100nf the results are top of the screen scan you get that waveform as in first picture ,then towards middle of scan down the results are as a line but i managed to grab a frame which shows its still a sine wave still oscillating ..
I had a 155 .....1.5uf a big jump and tried that as i was not sure why i am getting that waveform
The result is not what i expected as in the 3rd picture the waveform is greater now but no sinewave just a line with smaller waveform and smaller spikes .
I will wait to hear what you think ...

Re: Deflection ampilfiers

PostPosted: Thu Feb 23, 2017 12:16 am
by Klaas Robers
I don't know where the spikes are from. It must be something of 100 Hz hum in the power supply. Am i wrong that I see the spikes to be larger when the vertical scanning is at its beginning / end of the scan? That is when the current through the deflection coils are the largests. That is also when the power supply has to deliver the largest currents.

Harry, you have an oscilloscope. I guess that you see the "spikes" too in the slow sawtooth going to the vertical output amplifier. And then look on the +12 and -12 volt "rail".

But I also see that the "gap" in the vertical scanning is gone with the smaller capacitors.

To start with it is sensible that you make the scannings, horizontal and vertical smaller. There is no need to scanover the size of the screen. So make the scans smaller and place the scans in the centre. I have seen potentiometers in your circuit diagrams to do that.

Re: Deflection ampilfiers

PostPosted: Thu Feb 23, 2017 1:12 pm
by Harry Dalek
Klaas Robers wrote:I don't know where the spikes are from.


Hi Klass well i was thinking it might be the inverter some how ..to day move things around and switched it back on and the spikes were gone so seems likely /

It must be something of 100 Hz hum in the power supply. Am i wrong that I see the spikes to be larger when the vertical scanning is at its beginning / end of the scan? That is when the current through the deflection coils are the largests. That is also when the power supply has to deliver the largest currents.


Well it was top of the scan spikes most and faded away towards the middle to the bottom but they were gone on the test i just did ....only thing i can notice is a slight bending at the left hand start of the horizontal line but apart from that looks ok.

Harry, you have an oscilloscope. I guess that you see the "spikes" too in the slow sawtooth going to the vertical output amplifier. And then look on the +12 and -12 volt "rail".


The supply looked clean Klass on the scope...i hope it was a one off thing but knowing my luck :roll:

But I also see that the "gap" in the vertical scanning is gone with the smaller capacitors.



Yes sir you helped me fix that for sure i will go back now and test with the caps and see what i can end up using ..

To start with it is sensible that you make the scannings, horizontal and vertical smaller. There is no need to scanover the size of the screen. So make the scans smaller and place the scans in the centre. I have seen potentiometers in your circuit diagrams to do that.


I can adjust the left right up down of the scan not so much the size does not seem to do much even seeing on the scope the input size of the sawtooth is reduced again i think the 5 ohm 2 ohm resistors need increasing this will drop the scan size as that worked before i suppose you have to match these resistors to your yoke values.

Re: Deflection ampilfiers

PostPosted: Fri Feb 24, 2017 8:28 am
by Klaas Robers
No Harry, it is the other way around. The deflection amplifiers try to make the voltage over the 5 ohm or 2 ohm resistors equal to the input voltage (the sawtooth). If you make the value larger, there is less current in the coil, so the scan is made less wide.

So if you can't make the line short enough, increase the "bottom resistor".

Re: Deflection ampilfiers

PostPosted: Fri Feb 24, 2017 10:42 am
by Harry Dalek
Klaas Robers wrote:No Harry, it is the other way around. The deflection amplifiers try to make the voltage over the 5 ohm or 2 ohm resistors equal to the input voltage (the sawtooth). If you make the value larger, there is less current in the coil, so the scan is made less wide.

So if you can't make the line short enough, increase the "bottom resistor".



Sorry thats what i did mean Klass ..increasing those resistors to reduce the scan size ...\
This i have now done ......was horiizontal vertical were 2 an 5 ohm now 5 and 10 ohm that now seems to give a nice reduced size ..i suppose i could reduce an ohm on those resistors here and there get it a touch more square ///getting there .
A lot better than a few days ago on this side of things it just needs a little tweaking .
I might move on to looking at the modulating that beam .

Re: Deflection ampilfiers

PostPosted: Sat Feb 25, 2017 6:41 am
by Klaas Robers
Well done Harry, this is something that I recognize as an SSTV-screen. I don't know if the scan speeds are correct, but that can only be seen with modulation of the beam. Then you also have to tackle the synchronisation problem.

Re: Deflection ampilfiers

PostPosted: Sat Feb 25, 2017 7:06 pm
by Harry Dalek
Klaas Robers wrote:Well done Harry, this is something that I recognize as an SSTV-screen. I don't know if the scan speeds are correct, but that can only be seen with modulation of the beam. Then you also have to tackle the synchronisation problem.


Well i have finished tweaking it Klass the aspect ratio is adjustable now and seems to work well ...
The scan oscillator's are within range once i see beam modulated i can adjust those closer,i recall syncing these oscillators years ago may be 20 or more i remember having trouble getting it to sync the solution to hooking it up to the sync detection circuit was placing a diode between the circuits then it worked ..for me more trial and error .
But yes really have the sync detection to go now but beam modulation is where i will work on next as i could get a picture .