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Re: 120 and 180 line viewing

PostPosted: Fri Oct 13, 2017 7:27 am
by murphyv310
Hi.
Well I've decided to separate the EHT from the scanning. After a little search I found a suitable transformer for EHT generation. I'll leave the existing transformer for scanning .

Re: 120 and 180 line viewing

PostPosted: Fri Oct 13, 2017 1:39 pm
by Harry Dalek
murphyv310 wrote:Hi.
I've done three videos in parts of what I have done.
See here:
https://youtu.be/D-86YS7JqpA

https://youtu.be/qi2EG8BZoNY

https://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


Really great well detailed videos works very well at 240 lines .
Do you have a schematic of your set ? and the changes ? as this is on going i can understand it some times hard to jot it down on paper on PC these days .

Re: 120 and 180 line viewing

PostPosted: Fri Oct 13, 2017 7:54 pm
by murphyv310
Hi Harry.
Yes I'm working on it as I progress. Once I'm reasonably happy with it I will post it up here.

Re: 120 and 180 line viewing

PostPosted: Sun Oct 15, 2017 9:12 am
by murphyv310
240141017.jpg
240 Lines *** NOTE not 625 as per picture ****
180141017.jpg
180 lines


Hi.

Some further progress was made today.
Although the HT feed to the line output stage is stabilised it still wasn't that stable on the EHT side. Yesterday the EHT flashed over a couple of time on low brightness so I thought I should come up with a better solution.
I thought about using a series network of Avalanche diodes, after a rummage through the spares box I found a couple of dozen BYV95C Diodes. These are rated at 600v so I thought I'd put 9 in series and see if it would work. I carefully made up a network and insulated it with a few pieces of heat-shrink tubing and connected it to the CRT final anode after the smoothing circuit and feed resistors. I have to say this was a total success with 5500v on the anode irrespective of beam current, i did though up the HT to the line stage from 89v to 101v by adding an extra 10v zener to the shunt stabiliser.
I've now also got the G2 volts correct on the CRT. Focus is really good now.
I still need to do something with the frame circuit but I think the output transformer is the problem.

Re: 120 and 180 line viewing

PostPosted: Sun Oct 15, 2017 3:20 pm
by Robonz
Nice work Trevor, that vertical distortion looks more like a vertical amplifier problem than a transformer. I could be wrong. The picture quality looks great.

Cheers
Keith

Re: 120 and 180 line viewing

PostPosted: Tue Oct 17, 2017 4:08 am
by murphyv310
Hi.

I ave now succeeded in uploading some new images to the old Aurora.
I now have 120/24P... 180/25P & 240/25P.
I have improved the linearity on the frame somewhat but it still isn't brilliant, i am thinking the frame TX isn't up to 25 Hz and no further improvement can be made, same with the Striations on 240 lines, usual tricks with damping hasn't really helped, as we know the line stage is in starvation mode and extra loading damps it down. I don't want to go that way as the Jelly pot Isn't designed for these low speeds and i'd rather ensure it doesn't fail, the early 900 series types are exceptionally rare and I'd like to keep it going. To be fair this is very much an experiment anyway.
You'll see the corseness of 120 lines, the picture is way off centre but again the line stage is struggling at under 4Khz.

120 lines 120/24p
IMG_20171016_130922_resized_20171016_021445490.jpg

180 Lines
IMG_20171016_131200_resized_20171016_021447146.jpg

240 Lines
IMG_20171016_131220_resized_20171016_021355570.jpg

Re: 120 and 180 line viewing

PostPosted: Tue Oct 17, 2017 5:28 pm
by Harry Dalek
Trevor the setup by the looks of it does like 240 line over the lower line rates ...BTW how many line rates do you want it to do ...its a 405 line monitor yes ?

Re: 120 and 180 line viewing

PostPosted: Tue Oct 17, 2017 7:14 pm
by murphyv310
Hi.
I'm not bothered with 405 on this set as I have another TV22 that is a complete set with cabinet. I also have around a dozen other 405 sets from 1946 to 1968.
One other set that resolves 240 well is a 1951 Decca 1000 Projection TV. It is a forward projection type onto a 4 X 3 foot screen, the flicker on such a large screen is very annoying and more noticeable.
I would say at this time I'd concentrate more on 120, 180 & 240 on my project set.

Re: 120 and 180 line viewing

PostPosted: Tue Oct 17, 2017 7:45 pm
by Harry Dalek
murphyv310 wrote:Hi.
I'm not bothered with 405 on this set as I have another TV22 that is a complete set with cabinet. I also have around a dozen other 405 sets from 1946 to 1968.
One other set that resolves 240 well is a 1951 Decca 1000 Projection TV. It is a forward projection type onto a 4 X 3 foot screen, the flicker on such a large screen is very annoying and more noticeable.
I would say at this time I'd concentrate more on 120, 180 & 240 on my project set.


They are very rare here only ever tested in Australia in the late 1940's in one city , i think Melbourne was working on 625 line and Sydney tested 405 line ..i have never seen one up close .
Like with your 120 180 240 line i have to make one to have one ,and i understand pretty neat having your set do it yourself ! :wink:

Re: 120 and 180 line viewing

PostPosted: Fri Nov 03, 2017 9:44 am
by murphyv310
DSCF9017.JPG


Hi.
Since my last post the set has been playing up slightly with some hum modulating the picture.
This seems a common issue due to the old valve bases getting a little leaky and the AC from the heater pins interfering with the line oscillator and synch separator.
I have now replaced the bases in the Line Osc/Synch separator and changed the valve from an ECL80 to a 30FL1 also in the video amp from an EF91 to another 30FL1 wired as a pentode video amplifier followed by the triode section wired as a cathode follower. These mods have given me a little more line drive, also a higher video drive with better HF response.
I have also set my camera to manual settings and used a tripod for better pictures.

Re: 120 and 180 line viewing

PostPosted: Fri Nov 03, 2017 7:18 pm
by Harry Dalek
Looks excellent Trevor linearity looks great little long on the top but better than what i have done,your circuit changes look to have payed off here .

Re: 120 and 180 line viewing

PostPosted: Sat Nov 04, 2017 1:09 am
by murphyv310
TV22mod2.pdf
(693.91 KiB) Downloaded 230 times
TV22mod1.pdf
(808.32 KiB) Downloaded 222 times
OK so now I have drawn up two circuits, one for the Video modification and now one of the line timebase.
I am using a Thorn 900 lopt with the full EHT overwind, this has to be the best lopt for what we are doing, using a 950 or 1400 type will still need a doubler as the resultant EHT would be too low running the timebase on starvation mode. The snag is the red topped 900 lopt's are quite rare. Don't worry though if you want to try this use the doubler.
On the diagram you'll see T1. It's the blocking oscillator transformer, virtually any will work but values may need changing, I'm using one from an early Ferranti it's small and neat so can be fitted into the bush chassis with ease. Smoothing needs to be upped a bit as the 25 hz frame can breath a bit so an extra 100uf on the main HT line is added and a 22uf on the 105 volt line to line output is added. The screen grid feed to the PL36 is fed from the main HT line via a 5K this works the best, there is also a choke fitted to the PY81 cathode and it helps to suppress some of the line stage ringing, it is one of RS's 1 amp chokes but does the trick, no timebase tuning is required as it is running on very slow speeds and low HT so the ramp up time can not really be damped.
I also will later upload the circuit of the frame timebase.

Any errors I may have missed please let me know.

Re: 120 and 180 line viewing

PostPosted: Sat Nov 04, 2017 11:22 pm
by Harry Dalek
looks good Trevor ,i like also on old school hand drawn schematics .
Thanks for posting .

Re: 120 and 180 line viewing

PostPosted: Fri Nov 10, 2017 4:44 am
by Lowtone
180 line testcard C :mrgreen: nice touch

Re: 120 and 180 line viewing

PostPosted: Sat Nov 18, 2017 7:32 am
by murphyv310
Hi.
I've not been doing much on this or working out how to do syncs for mechanical standards. The shed is quite cold and I've not been at my best. Other things have had to take preference. Will get back into the swing of things soon.