5AHP7A Vintage SSTV The Deep image

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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Tue Feb 14, 2017 8:11 pm

Sorry Steve
I was not blaming your circuits or any thing using them here as i like them ...it really didn't sink in till now about the ramp needing to be as mentioned i can't say i have come across this before perhaps i need a inverting or non inverting opamp after the sawtooth generator ...i think i need to have a look at Klass's sawtooth circuits may be if i ask kindly he might post them up .
I have a deflection circuit working apart from its a bit wonky at the start of the scan i wanted to see if it could be improved on since i only have one of these crts i don't mind trying different circuits on it as once its done its done like a trip you don't want to see finished ... i am not good at designing stuff so i do tack this on to that in a trial and error way i have to learn by my mistakes what works and what doesn't .
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: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Wed Feb 15, 2017 4:44 pm

If you see this Klass i found your sstv monitor schematic i downloaded it to a folder last year .

A Question on the power rails your schematic shows you are using dual 6 volts but its 12 on the one posted a few posts ago ..its a big jump just checking if it matters or not .

Is the diode for blanking a 4.7 volt zener a guess since theres a voltage next to it ,i was not familiar with the symbol .

BTW came across this sstv on youtube wonder what tube that uses i didn't think it was a p7 till he turned it on...
https://www.youtube.com/watch?v=2tIfhI5XQTM
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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: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Thu Feb 16, 2017 7:11 am

Steve, would an emitter follower, NPN, resistor to - 12 volt, eventually a double emitterfollower (darlington) not solve the problem of uni polarity? Then the DC zero drops to - 1 volt, the impedance problem is solved, what do we need more?

Harry, I have seen that your horizontal scan line goes from the centre to the right. That indicates that it works any way, and it shows that the saw tooth goes only positive. The sawtooth that you have now, starts at zero and goes up positive. Two transistors and one resistor "shifts" all voltages about one volt negative and converts a high ohmic input to a low ohmic output. Exactly what you need in this case.

Steve, do you know the peak peak voltage of the sawtooth by heart? Is it easily adjusted to 2 volts? That would help Harry.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Thu Feb 16, 2017 11:41 am

Klaas Robers wrote:
Harry, I have seen that your horizontal scan line goes from the centre to the right. That indicates that it works any way, and it shows that the saw tooth goes only positive. The sawtooth that you have now, starts at zero and goes up positive. Two transistors and one resistor "shifts" all voltages about one volt negative and converts a high ohmic input to a low ohmic output. Exactly what you need in this case.


Sorry about that too Klass i was thinking it just needed either a positive or a negative sawtooth not one that swung from positive zero to negative so on i should get double the scan line width with the correct sawtooth swing.

Any case before i do any other construction i took on board you suggestion on the deflection yoke so took that off the crt and opened it up pretty clean for 59 years ...

Tried here to show you the connections and readings
Yellow out and green out ..40.2 ohm
Yellow out and red 1....... 20 ohm
Green out and red 1 ........20 ohm

Orange out and Blue out... 15 ohm
Orange out and red 2 .. ....15 ohm
Blue out and red 2...........15 ohm
Orange and red out ........30 ohm


So the deflection plug has yellow and green for one deflection yoke coil

And orange Blue or red for the other ...so i think 15 ohm and 20 ohm would be it .....lowing the coils resistance i was hoping to parallel them to get closer to yours but seems not or may be around the red blue and orange might be possible...Should i remove the cap and 56k resistors ? all the solder points on the yoke are connected to the coils.
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Last edited by Harry Dalek on Thu Feb 16, 2017 5:30 pm, edited 2 times in total.
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: 5AHP7A Vintage SSTV The Deep image

Postby Steve Anderson » Thu Feb 16, 2017 3:23 pm

Klaas Robers wrote:Steve, would an emitter follower, NPN, resistor to - 12 volt, eventually a double emitterfollower (darlington) not solve the problem of uni polarity? Then the DC zero drops to - 1 volt, the impedance problem is solved, what do we need more? Steve, do you know the peak peak voltage of the sawtooth by heart? Is it easily adjusted to 2 volts? That would help Harry.

Off the top of my head I think it's around 5V, 0v to +5. So some form of lossy buffer would do the trick with a bit of deliberate negative DC-shift. An NPN Darlington tranny could well be the answer here. say a MPSA13/14?

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Re: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Fri Feb 17, 2017 2:45 am

Harry, thanks for the clear description and the photograph of the deflection yoke. This helps a lot.

First I should do nothing yet on the circuiting of the deflection coils.
Use Yellow to Green for one deflection (40 ohm) and
use Orange to Red for the other deflection (30 ohm),
leave the Blue output wire floating, not connected.!

If you used blue as one connection for the deflection this could be the reason that your deflection field was not a square / rectangle.!

If this works and you can make a square that is large enough, the corners touching the circular edge of the screen, leave it as is.

If you cannot stretch the deflection enough, then your voltage is too low, you have to switch one (or both) of the coil sets from series into parallel. But that is a next story. I had to do that for one of my coil sets, but I had just +6 and -6 volts. You have +12 and -12 volts, and that helps a lot.

And there is no need to remove the resistors and the capacitor. The resistors are much larger in value than the coils where they are in parallel with, and the capacitor does no harm for the much much lower frequencies that we are using for SSTV.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Fri Feb 17, 2017 12:04 pm

Klaas Robers wrote:Harry, thanks for the clear description and the photograph of the deflection yoke. This helps a lot.


Glad it was more helpful i tried to take all the readings i could think of .

First I should do nothing yet on the circuiting of the deflection coils.


OK i have done nothing to them i have put it back on the crt as you see in the Gifs .

Use Yellow to Green for one deflection (40 ohm) and
use Orange to Red for the other deflection (30 ohm),
leave the Blue output wire floating, not connected.!


Yes that worked well ! much better what i did was hooked up the Radio communication hand book sstv sawtooth and deflection circuits as i could test both the horz and vertical.

If you used blue as one connection for the deflection this could be the reason that your deflection field was not a square / rectangle.!


You are right it looks more square to me i don't see any angle to the scan at the start as it first did using the 15 ohm which must of been half a vertical yoke coil .

If this works and you can make a square that is large enough, the corners touching the circular edge of the screen, leave it as is.


I have enough or fine adjustment to move this scan size to even it out up or down or side to side .

If you cannot stretch the deflection enough, then your voltage is too low, you have to switch one (or both) of the coil sets from series into parallel. But that is a next story. I had to do that for one of my coil sets, but I had just +6 and -6 volts. You have +12 and -12 volts, and that helps a lot.


It seems fine on 12 volts but the circuit does say dual 10 volts

And there is no need to remove the resistors and the capacitor. The resistors are much larger in value than the coils where they are in parallel with, and the capacitor does no harm for the much much lower frequencies that we are using for SSTV.
[/quote]

OK just leave them no problems ...will do .

There seems to be one problem with the circuit i have noticed and i am not sure why half way down the scan its like it skips 2 lines or so not so prominent on a slow scan with more lines but very much so on fewer lines you can see it on the bottom Gif towards the center of the scan ...i have been trying to work out why this is happening ..but i am so far puzzled .
This is the circuit again used on the vertical side ,,,
I can still go with your design if you feel it would work better i am fine with trying different ideas.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Sat Feb 18, 2017 8:55 am

What I see is that the vertical scanning has a hic-up in the middle. This is to be expected, because the two output transistors have their emitters connected AND their two basis. This is a standard circuit for maximal cross over distortion. And that distortion is what you see. The vertical scan stops moving for one or two lines and then continue as it was going. So you see two lines on top of each other, and than one or two lines missing. This is why I have the 2k potmeter between the basises.

But I can advise you to do nothing to cure this at this moment, look over this effect and go on with the SSTV monitor. This is a known problem, that you may solve later.

By the way, in the horizontal line something similar happens in the middle, but you cannot see that so easily. You will see that later, when there is video and you see diagonal lines on the screen. Sam problem, same solution. Not yet.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Sat Feb 18, 2017 4:11 pm

Klaas Robers wrote:What I see is that the vertical scanning has a hic-up in the middle. This is to be expected, because the two output transistors have their emitters connected AND their two basis. This is a standard circuit for maximal cross over distortion. And that distortion is what you see. The vertical scan stops moving for one or two lines and then continue as it was going. So you see two lines on top of each other, and than one or two lines missing. This is why I have the 2k potmeter between the basises.

But I can advise you to do nothing to cure this at this moment, look over this effect and go on with the SSTV monitor. This is a known problem, that you may solve later.

By the way, in the horizontal line something similar happens in the middle, but you cannot see that so easily. You will see that later, when there is video and you see diagonal lines on the screen. Sam problem, same solution. Not yet.


Thanks Klass
that makes me feel better ,i was worried it may be a problem with the yoke on this crt more than the electronics .
I went back to my videos from yesterday to one video i took before i straightened up the yoke and adjusted the horizontal line position so the edge of the horizontal scan line shows up on the right side of the display ...theres a slight wobble i wonder if that is the distortion you have mentioned ..i was thinking it was good to show if so .
OK i will work on so other parts of the monitor and leave this be for now /
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Steve Anderson » Sat Feb 18, 2017 6:43 pm

I would have thought that the negative feedback would have virtually eliminated that 'flat spot' in the deflection waveform. Perhaps there's less open-loop gain than I would have expected.

What i'm surprised about is why devices like a TDA2030/40/50 haven't been used here? Although touted as audio amplifiers what are they really? Power op-amps...designed to drive inductive loads (loudspeakers), so I would have thought ideal for this use. Maybe with slightly modified compensation due to the larger yoke inductance, though the current feedback resistor should help in taming that.

Their down-side is I find the quiescent current a little high (around 50mA). Not really a problem in an application like this, but in audio use they do run a bit warm even with no audio is being output. They've been around for many years and are cheap, I don't understand why less quiescent power-hungry devices been developed?

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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Sat Feb 18, 2017 8:06 pm

Steve Anderson wrote:I would have thought that the negative feedback would have virtually eliminated that 'flat spot' in the deflection waveform. Perhaps there's less open-loop gain than I would have expected.

What i'm surprised about is why devices like a TDA2030/40/50 haven't been used here? Although touted as audio amplifiers what are they really? Power op-amps...designed to drive inductive loads (loudspeakers), so I would have thought ideal for this use. Maybe with slightly modified compensation due to the larger yoke inductance, though the current feedback resistor should help in taming that.

Their down-side is I find the quiescent current a little high (around 50mA). Not really a problem in an application like this, but in audio use they do run a bit warm even with no audio is being output. They've been around for many years and are cheap, I don't understand why less quiescent power-hungry devices been developed?

Steve A.


Hi Steve you reminded me with this post that Graham has pretty much used this driving he's NBTV camera yoke on my failed attempt the TDA audio amp was one thing that did work fine least something worked one photo to prove it .
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Steve Anderson » Sat Feb 18, 2017 9:13 pm

Yep, you'd probably need more drive (+12 & -12 supplies) for a CRT deflection yoke, but the idea is the same. I must admit I had forgotten about Graham's use of these devices here. They probably would be needing a heatsink by this stage.

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Re: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Sat Feb 18, 2017 9:41 pm

Harry, if I look at the pencil drawn circuit diagram, I see that from the two connected bases of the final deflection transistors, there is a capacitor to ground. Can you look for the value of that capacitor? It should be as low as possible, I guess 1000 down to 100 pF. This capacitor is there only to keep the deflection amplifier quiet, not oscillating. I guess that at least in the vertical amplifier there is now a much higher capacitor mounted.

You can optimise it by trial and error, make it smaller and smaller, until the amplifier starts oscillating, but first mount a resistor of .... 470 ohm over the deflection coil. You will observe oscillation very well, because the line then gets "thick". If that happens, make the capacitor twice that value and keep it that value.

This aplies too for the horizontal deflection stage. If you obtained the capacitor value for the vertical stage, this can be used in the horizontal amplifier as well.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Sat Feb 18, 2017 9:51 pm

Make a square scanning field. I guess that the horizontal sawtooth generator also has the 22k potentiometer in the bottom of the diagram, to -12 volt. With that potentiometer you can shift the horizontal scan to the right, and then with the 2k2 you may readjust the amplitude. Both interact somewhat, so adjust them in an alternating way.

As it is the scan line starts out of the viewing area so you will not see the most left part of the video, the beginning of the lines.
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Sun Feb 19, 2017 7:12 pm

Klaas Robers wrote:Harry, if I look at the pencil drawn circuit diagram, I see that from the two connected bases of the final deflection transistors, there is a capacitor to ground. Can you look for the value of that capacitor? It should be as low as possible, I guess 1000 down to 100 pF. This capacitor is there only to keep the deflection amplifier quiet, not oscillating. I guess that at least in the vertical amplifier there is now a much higher capacitor mounted.

You can optimise it by trial and error, make it smaller and smaller, until the amplifier starts oscillating, but first mount a resistor of .... 470 ohm over the deflection coil. You will observe oscillation very well, because the line then gets "thick". If that happens, make the capacitor twice that value and keep it that value.

This aplies too for the horizontal deflection stage. If you obtained the capacitor value for the vertical stage, this can be used in the horizontal amplifier as well.



OK Klass i have fixed up the pencil drawing a bit changes i made .

The cap to ground is a 470 uf polarised on the vertical ,the horizontal the cap is 130 nF not a pf so way off your suggestion do you think i should change the caps ? .

I tried the 470 ohm experiment i didn't really notice the raster line getting thicker it tended to on the vertical drop the scan a touch top and bottom as in height and horizontal a very slight narrowing of line width then again with my eyes i was wondering why the raster line was blurry then i put my glasses on that helped :wink:

Perhaps i need to change those capacitors and do the test again ?

I made a better copy of the original schematics from the radio communication hand book ....a few changes as in the drawing schematic all transistors are same in the vert and horizonal as in that part list .
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