Passive Cathode ray tube modulation

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Passive Cathode ray tube modulation

Postby Harry Dalek » Sun Oct 28, 2018 7:21 pm

Well i needed my little trio scope to do some z axis modulation to test some video file's out and see how accurate the FSC clock sawtooth circuits are ,and what i thought was the problem on the scope a 10nf 2kv cap seems fine as well as all resistors so i just left it after replacing the capacitor and recalled something i did 2 decade's ago and thought i would try and see if my vague memory of it was correct .
So the procedure after the schematic is brake the connection for the cathode pin 3 and connect a spare mains transformers primary between that and pin 22 rest explained below schematic .
IMG_0107.JPG

Pretty much a very simple idea i don't know if it has been used in the past by any one else ,pretty much the idea was and is just using a small mains transformer the primary 240 volt side is used between the cathode and its negative 1500 volt supply ...so only 2 connections .
The secondary which i think would of been 12 volts side is used for the modulation input just connected right from the lap top to ground and signal output connection just another 2 connections to that secondary .
So small signal about a 1 volt or so at best can modulation your scope if you don't have a Z axis connection .
It does rely on how high the video level is but every thing i tried seemed to work some files better than others but had not used any thing apart from this passive induction amplifier .
A speaker audio transformer i think would also work more than likely ,i was surprised it still worked without the one transistor amplifier i also recalled i used back then .
So results below upside down and reversed ...least its not inverted :wink: I will add a video amplifier transistor to this but for using a little transformer and 4 connections a quick and dirty z axis modulation .
Attachments
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IMG_0112.JPG
IMG_0121.JPG
IMG_0076.JPG
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Re: Passive Cathode ray tube modulation

Postby Steve Anderson » Tue Oct 30, 2018 1:54 pm

Yes, very simple, it is only AC-coupled, but it will give you a picture.

One thing I will mention - don't use an old transformer that's been kicking around in a damp shed for years - the insulation may not be up to holding off 1500V. Use a brand new one. They are (should be) flash tested at the factory to at least 2.5kV between primary and secondary.

If that insulation fails say goodbye to your laptop...

Steve A.
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Re: Passive Cathode ray tube modulation

Postby Harry Dalek » Tue Oct 30, 2018 4:10 pm

Steve Anderson wrote:Yes, very simple, it is only AC-coupled, but it will give you a picture.

One thing I will mention - don't use an old transformer that's been kicking around in a damp shed for years - the insulation may not be up to holding off 1500V. Use a brand new one. They are (should be) flash tested at the factory to at least 2.5kV between primary and secondary.

If that insulation fails say goodbye to your laptop...

Steve A.


Yes it is pretty simple idea Steve i forgot got all about it for a long time and does isolate the negative 1500 KV from the signal .
Yes i am using a newer transformer not some old rusty thing i also stayed away from something too tiny but for ...sure yes don't want any voltage jumping but seems fine from the testing the other day .
Procedure i did was lower the scopes luminance so its trace line is just off being seen and i tapped a low voltage cross the secondary, i had a resistor wheel here too to see how low i could go and see an effect on the intensity...and does not need much at all a lap top you are lucky if it can light a led.
Pretty easy add on for any scope without a z axis connection ,
I am very curious if it would work on a magnetic tube , when i replace my circuits i will give it a go .
Attachments
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IMG_0037.JPG
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: Passive Cathode ray tube modulation

Postby Steve Anderson » Tue Oct 30, 2018 7:19 pm

Yep, it should work exactly in the same manner with a magnetically deflected CRT, depending on the CRT's characteristics and the applied voltages you may need more or less signal.

Though it probably wouldn't make that much difference, it may be a worthwhile thing trying a valve/tube audio output transformer also used in reverse. They should have a better frequency response than a transformer designed for 50/60Hz only. But it's probably not going to be that visible. What you've shown so far looks quite good.

Also the turns ratio in the transformer will affect the amount of signal required. With a 240V-12V transformer that's 20:1, a valve/tube output transformer could have a quite different turns ratio depending on the nominal impedance of the windings/tube (valve) operating conditions/loudspeaker impedance.

Steve A.

A few stabs at the calculator later...yer average table-top radio from the 50's may have used an EL84/6BQ5 output tube/valve. To match the tube/valve to the loudspeaker also results in a turns ratio of around 20:1 or thereabouts...
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Re: Passive Cathode ray tube modulation

Postby Harry Dalek » Tue Oct 30, 2018 10:23 pm

Steve Anderson wrote:Yep, it should work exactly in the same manner with a magnetically deflected CRT, depending on the CRT's characteristics and the applied voltages you may need more or less signal.


I am glad to hear you think its possible as well ,i will try it in the next few days

Though it probably wouldn't make that much difference, it may be a worthwhile thing trying a valve/tube audio output transformer also used in reverse. They should have a better frequency response than a transformer designed for 50/60Hz only. But it's probably not going to be that visible. What you've shown so far looks quite good.


I think i did 20 years ago as i had a few valve speaker transformers but i don't recall which i ended up using the mains transformer or one of those knowing more about the voltages this time around i thought it saver to try the mains one ..i had 2 old valve speaker transformers i found but they were covered in Tar i don't know the reasoning why they did that back then but put me off trying these this time also .
Yes the transformers bandwidth is a factor i should do a frequency sweep test on both and see the mains transformer seems to do well for NBTV bandwidth on 32 line ,i could try double 64 line and see .

Also the turns ratio in the transformer will affect the amount of signal required. With a 240V-12V transformer that's 20:1, a valve/tube output transformer could have a quite different turns ratio depending on the nominal impedance of the windings/tube (valve) operating conditions/loudspeaker impedance.

Steve A.


By chance the secondary must be close enough a match its more than enough for it to work ,i have to say this is the first time i have tried this without a video amplifier transistor driving the secondary coil i was very pleased it still worked .

A few stabs at the calculator later...yer average table-top radio from the 50's may have used an EL84/6BQ5 output tube/valve. To match the tube/valve to the loudspeaker also results in a turns ratio of around 20:1 or thereabouts...

[/quote]

So about the same ratio as the mains transformer that's a good reason you would expect same sort of results on the modulation side of things ..
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Re: Passive Cathode ray tube modulation

Postby Harry Dalek » Fri Nov 02, 2018 10:49 pm

Tried this little circuit to day for the weaker video files ,i had to use Steve your video inverter circuit from the A for Anderson monitor as just using the class A amplifier for the video modulation the video ended up inverted on the Screen ....its far from perfect results so far but its ok .
Adding resistance across the Secondary coil being driven improved the video result ,just really tried this for weaker signal video files.
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I tried 64 line the other day found an effect on the screen i was not expecting half 64 and half 32 not sure the saw tooth looks correct might be my scope don't think its the modulation but the transformer does seem to have more band width .
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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: Passive Cathode ray tube modulation

Postby Andrew Davie » Sat Nov 03, 2018 12:31 am

That last picture would be Louise Brooks, I reckon.
Very interesting work!
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Re: Passive Cathode ray tube modulation

Postby Harry Dalek » Sat Nov 03, 2018 10:00 am

Andrew Davie wrote:That last picture would be Louise Brooks, I reckon.
Very interesting work!


Yes you could be right Andrew ,i am playing with the modulation at the moment some thing i didn't think would matter is if you just reverse the secondary input windings from audio input to ground visa versa it reverse's the video ! i must of just lucked it first time try for normal video .
Trying a transformer with a 6 volt secondary winding works better twice the modulation by the looks of it .
Reason i am also testing on the scope i still have to sync the signal slight drift just free running the circuit;s via the crystal oscillator .
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: Passive Cathode ray tube modulation

Postby Steve Anderson » Sat Nov 03, 2018 1:05 pm

Harry, I'm surprised you're getting such a usable signal out of the TL071, it really is almost useless at just 5V...this applies to most op-amps not designed for low voltage operation.

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Re: Passive Cathode ray tube modulation

Postby Harry Dalek » Sat Nov 03, 2018 6:17 pm

Steve Anderson wrote:Harry, I'm surprised you're getting such a usable signal out of the TL071, it really is almost useless at just 5V...this applies to most op-amps not designed for low voltage operation.

Steve A.


Hi Steve yes it works very well at 5 volts ,i will explain why i am using it at 5 volts here .
I am trying today using the transformer modulation and this time using your circuit posted below as is , but ic601 is a Tl071 ......i have a 33uf n/p cap on pin 6 the other end of that cap now connects to a new transformer with the secondary now 6 volt secondary transformer other end of the secondary is grounded .
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Using 5 volts the video is pretty clean but if i use 12 volts the signal is to strong every thing looks washed out i will try and take some pic's .
5 volts used below
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12 volts every thing washed out over amplified perhaps
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i was looking at a data sheet its says the operating range is
VCC+ Supply voltage (1) 5 15 V
VCC– Supply voltage (1) –5 –15 V
VCM Common-mode voltage VCC– + 4 VCC+ V
maximum 0.3 to 36 v
Here experimenting i was just viewing the results 5 volts seems to work best here.....

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Looking into the syncing problem.....

Steve some anti head scratching advice i was also looking in to the M/R reset of the 4040 in line frame ramp circuits would you suggest i make the 4538 mono circuit also below and connect connect the out puts of those to the pin 11 of the line and frame 4040's in case i am missing some thing before i construct .
from past experiments it was fine for 32 spot on in fact but and less so for higher line rates ,here 32 line is fine for now,just wondering if you think the 4040's reset would sync to the 4538's ? if its a see and find out i will just have to try .
At the moment the clock is a crystal so it lets me view but i do get a very slow roll with no syncing at all .

Line %26 Frame Ramp Generators l.gif

circuits.jpg
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: Passive Cathode ray tube modulation

Postby Harry Dalek » Sun Nov 04, 2018 7:08 pm

I worked out on the problem i had with the half 64 and half 32 line i just had some solder splatter between 2 connections of the 4040 good reason for what i was seeing .
Any case gave me a chance to test the 64 line without that problem and go up and try some 128 line files i had handy .
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64 line
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64 line
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128 line
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Below i am experimenting with 128 line with just the crystal no syncing the below 2 videos give's you an idea of the speed increase roll at this line rate ,at 32 line its so slow you can just about lock it but a bit of a roll at 128 /




Below i had a few 128 line videos i made a while back i had to display , so what i had handy here and what photos came out .
i used here just the original idea just the lap top to the mains transformer secondary winding's to modulate the cathode ...remember depending on which of the windings are on earth or output audio of the lap top the video will be either inverted or normal with no electronics doing this only magnetism varying current direction in the secondary coil effecting the primary a varying electromotive force i suppose in a positive or negative direction effecting the voltage to the cathode /
IMG_0565.JPG
128 line Mr Frank

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128 line vampira
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128 line cyclops
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Attachments
MVI_0571_x264.mp4
128 line
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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: Passive Cathode ray tube modulation

Postby Harry Dalek » Sun Nov 18, 2018 9:46 pm

The last tests were done with the DAC FSC circuit ,got me thinking knocking together the Analog Anderson monitor circuit another of Steve's circuits used a few times could be an more simple way of doing the same thing on the FSC project so gave me the chance to test it here first using scope passive modulation again .
I only really changed Ic703 A and B for some screen position and raster size control also some timing switches i wanted to switch in for different line rates with out adjusting trimmers every time .
i only have line sync here no frame the 4538 monos i hoped to use here were faulty i will have to replace ...but any case line syncs from pin 6 ic602 for now pretty well for a quick solution .
Circuits below /i have not added my add on changes here....64 line in the short video

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NBTV Sybc Sep Initial 3.gif
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3BP1 NBTV Sawtooth 3.gif

Attachments
MVI_0640_x264_001.mp4
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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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