120 and 180 line viewing

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

Re: 120 and 180 line viewing

Postby Panrock » Thu Jul 31, 2014 9:09 pm

Now upside down.... bring it up on the variac. Smoke!!! Oh dear....

Note blackened resistor in one of the RF compartments. Details to follow after I return from my haircut...

Steve O
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Re: 120 and 180 line viewing

Postby Panrock » Fri Aug 01, 2014 12:33 am

The blackened resistor is R6 (4K7) in the anode leg of V2. The overload was caused by an internal leak in V2 (EF50), which obviously didn't like working upside down. This was promptly despatched to the bin and replaced. The original charred resistor has retained its value quite well, so since this isn't a commercial job and out of sheer laziness, I have left it in.

On to the hum. Actually this is sort-of livable with and only really shows on 24Hz frame rate standards. Bridging all the various HT rails with a whacking great 560uF didn't make a blind bit of difference, so its origin must lie elsewhere.

Next I shall try Steve A's suggestion to improve the vertical flyback...
Though I wouldn't go any more than half/twice the current values. Say 330nF for C43. (8M or so for R49).

Not sure where you got the '330nF' from though, Steve A. C43 is already only 10nF and now wants halving.

Steve O
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Re: 120 and 180 line viewing

Postby Panrock » Fri Aug 01, 2014 4:52 am

I was able to work on this all day today. State of play.gif (at the bottom) shows the current values of all components and the ones that have been changed are highlighted.

R49 was increased, C43 was reduced.
C49 was increased, R55 was reduced.

After this, there was too much height.
I swopped over the X and Y plate connections, but this made it still worse.

I put the X and Y back to how they were and increased Height Pot VR6 to its full value (by removing a parallel resistor found across it). This gave good control of height.

With the consequent reduction in load, the HT increased slightly, necessitating adjustment to line speed capacitor C53. The line hold control just nicely covers the 120 to 240 line range.

Basically, the previous flyback line problem has been exchanged for a vertical linearity problem.

I'm thinking of putting back C49 and R55 back as they were, to improve the linearity (?)

Steve O
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Re: 120 and 180 line viewing

Postby Steve Anderson » Fri Aug 01, 2014 1:33 pm

I have re-checked the (very) original values for C43 (anode-grid of V17), listed as 0.5uF (500nF to you and I) - hence why I suggested 330nF. Perhaps there was a later change or an errata issued? I'm using the March 1952 p458 version of the parts list.

You do have the advantage that the thing is right in front of you and you can try things and probe around until it's the way you wish. As best as is possible with designs of this vintage that is. But all credit to them, only 21 tubes (active devices) and 4-5 of them were diodes/rectifiers for a complete TV receiver with sound. Many of the tubes were war-surplus at the time implying there were better tubes around but at higher prices probably. They were keen to keep this below 20 quid in 1952 terms.

I think it's a case of you tweaking things bit by bit now, but if something else crops up I am here (as are others of course).

Steve A.

The non-linearity could be now there appears more gain the inverter tube is crushing the waveform. Ideally you want to keep the supply as high as possible (VR6 as low as possibe) and reduce the signal amplitude. I would need to study some works on this topology to figure out how the trigger points are derived in self-oscillating mode without sync pulses present.
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Re: 120 and 180 line viewing

Postby Panrock » Fri Aug 01, 2014 7:43 pm

Hi Steve A
Steve Anderson wrote: Perhaps there was a later change or an errata issued? I'm using the March 1952 p458 version of the parts list.

There was indeed. The original value of C43 was a misprint right from the start - as noted in my 'list of changes on the Argus site. The correct original value for 50Hz working was 10nF. Sorry, I thought you were working from the schematics I've posted on this thread, which have been kept updated and take account of this.

Steve Anderson wrote:You do have the advantage that the thing is right in front of you and you can try things and probe around until it's the way you wish. As best as is possible with designs of this vintage that is. But all credit to them, only 21 tubes (active devices) and 4-5 of them were diodes/rectifiers for a complete TV receiver with sound. Many of the tubes were war-surplus at the time implying there were better tubes around but at higher prices probably. They were keen to keep this below 20 quid in 1952 terms.

All the more reason to accept something slightly less than perfection! This morning, I've returned C49 to 1nF but left everything otherwise as it is in state of play.gif. The linearity is now improved. I think we could leave the frame section alone now.

So that's basically it. I now have a good working-120-240 line Argus! Thanks for the part you have played. :)

However, there's one final query I would like to pose if I may.... Would frame flyback suppression be worth a punt? This might just clean up that last straggly line or two at the top of the picture.

Steve O
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Re: 120 and 180 line viewing

Postby Steve Anderson » Sat Aug 02, 2014 8:20 pm

Panrock wrote:....Would frame flyback suppression be worth a punt? This might just clean up that last straggly line or two at the top of the picture. Steve O


Yes it would. But I would prefer to get the timebase(s) sorted out properly such that flyback suppression/blanking isn't required. i.e. still investigate why it's taking so long to retrace, These SP61's are supposedly RF pentodes so there should be no excuse. Adding blanking would probably require an additional tube too. If it were OK at 405 it should be OK too at slower line-rates - though this does depend on the blanking out of the Aurora. Some standards were quite mean with their frame/field blanking.

The trouble is that I'm not there with 'scope-probe in hand to find out why.

Steve A.
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Re: 120 and 180 line viewing

Postby Panrock » Sun Aug 03, 2014 6:34 am

Some final pictures. I guess it would be possible to bridge (to slightly reduce) one or other of the anode loads - they are somewhat inaccessible - or experiment with individual valves to further improve the linearity.... but life's short. Time to put it away.

Steve O
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Re: 120 and 180 line viewing

Postby Panrock » Sun Aug 03, 2014 7:07 am

And here's a Test Card at 120-lines. I have just swapped round V17 and V18. Sorry about the reflection of my computer monitor off the screen... maybe should have examined the bottom of the picture too, when setting the focus. Tough. Remember this is a 6:5 format. That's why the Test Card's sides are trimmed.

That'll have to do now. Thanks to all for viewing, and particularly of course to Steve A.

Steve O
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Re: 120 and 180 line viewing

Postby murphyv310 » Sun Oct 08, 2017 7:11 pm

Hi.
I've been doing something similar here: http://golbornevintageradio.co.uk/forum ... p?tid=6537

I have had a scrap Bush TV22 chassis lying around for some time with a burned out line transformer and a CRT that was down to air. I have now reasonably good results on 180 & 240 lines. There is still work to be done and also a cabinet to find. I've had very little response on the thread though and it makes me wonder if the hobby and interest is dying out? I'll be updating the thread in due course.
Cheers Trevor.
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Re: 120 and 180 line viewing

Postby murphyv310 » Tue Oct 10, 2017 5:48 am

IMG_20171008_165931.jpg
Hi.
I'll keep at the set I think. Today I have been working on the power supplies. I'm using a capacitor for the series fed heaters of 5.1uf instead of a dropper resistor network. One reason for carrying on is to try 120 lines, on the"PAL" input setting of the old Aurora Multi Standard converter 120 lines is a mechanical derived standard without of course normal electronic syncs. This of course is something I'd need help with.
I'll update here in due course.

The above picture is actually 240 lines.
Cheers Trevor.
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Re: 120 and 180 line viewing

Postby Harry Dalek » Tue Oct 10, 2017 8:06 pm

Hi Trevor it isn't dying out here i like it ,the monitor you have fixed up looks to be giving great results i hope mine can work as good one day .
I am trying to make one from scratch
viewtopic.php?f=15&t=2436
I don't have or didn't have any video signal reason i am working on a multi system flying spot camera idea for the higher line rates so i can test and display some thing on that monitor
viewforum.php?f=31
I will have a look at your posts on the other forum might some ideas there for me ...Just been looking at the CRT used you could make it a different multisystem and do Slow scan television as well .
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Re: 120 and 180 line viewing

Postby murphyv310 » Thu Oct 12, 2017 3:05 am

Hi Harry.
Many thanks for your nice words. it has spurred me on to do some more last night and today.
Most of the parts for all the modifications have come from the "junk box" but there were a few things I needed that I don't have.
One of the things I have been short of was a suitable capacitor for EHT smoothing. I did fit a 0.1uF rated at 6Kv, the value was OTT and 6Kv didn't really have enough headroom so I have ordered some 1nF at 10kV from RS. These will be ideal. The other thing that the modification needs is some form of line stage regulation. Adjusting the line frequency between standards and setting brightness and contrast changes width and EHT voltage, the reason for this is the use of a large value resistor to get the timebase running at a low voltage. The line scan transformer is intended for a 19 or 23 inch CRT with 110 degree deflection with 16 to 18Kv. I only need 6-7Kv and a scan deflection of 57 degrees.
I have found between 95 to 100 volts, the timebase runs beautifully. So today I added a very basic shunt regulator using a BU2508 line output transistor as a regulator, a zener diode and one additional resistor. The feed to the line output stage is now a solid 98 volts irrespective of brightness or line frequency. The transistor is bolted to the chassis and is running cold.
I still need to sort out a little amount of striations on the left hand of the picture and frame linearity, once the new caps arrive I'll work on the EHT side.
Cheers Trevor.
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Re: 120 and 180 line viewing

Postby Panrock » Thu Oct 12, 2017 5:35 am

Hi Trevor!

Well done with these results. Particularly as you have done it 'the hard way' with LOPT-style EHT.

One reason for carrying on is to try 120 lines, on the"PAL" input setting of the old Aurora Multi Standard converter 120 lines is a mechanical derived standard without of course normal electronic syncs. This of course is something I'd need help with.


Maybe my Aurora is a later model, but it provides two 120-line standards; one is 'electronic' so should have syncs.

Of course my best 120-line picture is now from the mirror screw. Colour too, and a 'lineless' picture, since the thickness of the mirror slat edges exactly fill each line. However you now have the problem of ensuring the exact timing of each line is correct, which is something that doesn't bother you on an electronic display.

Frustratingly hard to photograph too, since to get the correct aspect ratio you have to view it from several yards away! However there's a video on YouTube.

Steve O
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Re: 120 and 180 line viewing

Postby Harry Dalek » Thu Oct 12, 2017 11:18 am

murphyv310 wrote:Hi Harry.
Many thanks for your nice words.


No problems as Steve mentioned its a great display thanks for posting here or i would of missed it ,i am a member of the forum you posted to but i forgot about it i mainly hang around here :wink:

it has spurred me on to do some more last night and today.


Thats good keep on going its a beautiful display ,i hope mine can get to that stage ,i am using an old magnetic small CRT have no information to so all trial and error ,i will b e right if i can get the horizontal sweep a touch better .

Most of the parts for all the modifications have come from the "junk box" but there were a few things I needed that I don't have.


That's even better using junked parts spare parts handy to fix it ,don't really have tv's that size laying around that i have even see here our displays started large from the start so ,if you collect tv's here you better have room their all around the same size big !

One of the things I have been short of was a suitable capacitor for EHT smoothing.


This was a problem i thought i had when making the SSTV i wasn't saw till testing but the little HV module from china worked fine see construction diary it sure saved room as well using that .
viewforum.php?f=19

I did fit a 0.1uF rated at 6Kv, the value was OTT and 6Kv didn't really have enough headroom so I have ordered some 1nF at 10kV from RS.


Yes HV caps are hard to find only ones i have are from scrapping tv's never good to use a low lower voltage one they all die quick .

These will be ideal. The other thing that the modification needs is some form of line stage regulation. Adjusting the line frequency between standards and setting brightness and contrast changes width and EHT voltage, the reason for this is the use of a large value resistor to get the timebase running at a low voltage. The line scan transformer is intended for a 19 or 23 inch CRT with 110 degree deflection with 16 to 18Kv. I only need 6-7Kv and a scan deflection of 57 degrees.


Thats the problem using the line frequency to get the EHT i never do this i just make its own circuit to make the EHT if you noticed my Youtube video no change to raster size 32 to 1000 lines apart from lines matching up closer as they should ...if you don't mind changing the circuit and just make an oscillator and used a valve as you are now to drive the eht transformer it would fix you problem out right .
You could have more than 2 standards as i do .

I have found between 95 to 100 volts, the timebase runs beautifully. So today I added a very basic shunt regulator using a BU2508 line output transistor as a regulator, a zener diode and one additional resistor. The feed to the line output stage is now a solid 98 volts irrespective of brightness or line frequency. The transistor is bolted to the chassis and is running cold.
I still need to sort out a little amount of striations on the left hand of the picture and frame linearity, once the new caps arrive I'll work on the EHT side.


It sounds like you don't mind changing the circuits to make them work ,these things are all trial and error again on the EHT side just make is own circuit so its not effected but frequency change so EHT voltage change ...any case you must be close picture looks great .
Last edited by Harry Dalek on Fri Oct 13, 2017 1:09 pm, edited 1 time in total.
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Re: 120 and 180 line viewing

Postby murphyv310 » Fri Oct 13, 2017 3:07 am

Hi.
I've done three videos in parts of what I have done.
See here:
https://youtu.be/D-86YS7JqpA


youtu.be/D-86YS7JqpA

https://youtu.be/qi2EG8BZoNY


youtu.be/qi2EG8BZoNY

https://youtu.be/TP9wwzmpNgA


youtu.be/TP9wwzmpNgA

Harry & Steve.
Many thanks for your advice. I will certainly take heed of what is said.
I'd prefer separate EHT and it's not off the cards as yet.
Watch this space :D
Cheers Trevor.
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