Winter project.

[Murphyv310]

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

[Murphyv310]

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 5500Kv 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.
Pictures..... Test card F= 180 lines    

..................Test card C is actually 240 lines     

[peter scott]

Yes, it's not the 240 lines that make the Baird standard unacceptable. It's the flicker.

Peter

[Murphyv310]

Hi.
Iv'e been trying to upload three new imaged to my Multistandard Aurora to day. 180 lines has worked fine but 240 and the image is huge.
120 didn't work at all on the NTSC setting and feeding it with an NTSC Test card C.
Any ideas?

[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    

180 Lines    

240 Lines    

[Murphyv310]

Hi.
The project set has proved very reliable over the last few days. I've remade the EHT rectifier and stabilizer into a new housing and potted it. The only issue is some frame linearity drift after half an hour or so.
I also have set about drawing out the circuit manually, like Picasso though there are a few attempts in the bin.
I'll get it right though in the end.

[ppppenguin]

Since Trevor has re-awekened the thread about using Z mod on a scope I had a look back through the whole thread. We were discussing what sort of CRT to use and I suggested that magnetic scanning might well be OK at lower line rates: http://golbornevintageradio.co.uk/forum/...p?tid=5982&pid=63629#pid63629

Trevor managed to do better than my suggestion that a separate EHT supply would be needed. He's managed to stabilise the existing flyback EHT by very simple means.

[Murphyv310]

Thanks Jeffrey.
I'm all red with embarrassment.
Being fair I am more than surprised this has worked so well, I really think using the Jellypot in starvation mode is the secret.
I have another TV22 that I fitted a 900 Jellypot LOPT and I did this leaving in the PZ30 and using a 30P4 line output valve, the Line stage runs at 110 volts with no stabilisation, it has a Plessey Blocking oscillator transformer but a different circuit to the latest modded set. My earlier TV22 is brilliant, the picture is extremely bright and works very well indeed.

On this set I have two very simple shunt regulators, one for HT as it changes dependent on line frequency as does the EHT even with stabilised HT to the line stage, the EHT is stabilised at 5400v (says 5500 on my EHT meter) which is 1400v above the minimum of the tube, this is done with 9, 600v avalanche diodes.
Results are impressively good on 240 & 180 at 120 lines it is noticeably poor, very difficult to read smaller writing and making out a face that is any smaller than a third of the area of the screen difficult. On the scope the lower standards are even worse, not a bit of entertainment value at all.

I've actually recorded a test card onto minidisc on 90 lines onto one channel and sync onto the opposite channel and this works too rather blurry though. Oh what fun!!!!d

[ppppenguin]

TBH, I'm also surprised it has worked so well. The sums really don't add up if you try to run a LOP stage well away from its original design frequency, especially if it's also making EHT. As Trevor realised very early on, you need lower HT at lower scan rates. I guess it helps that a modern jellypot is more efficient than a 1950s era LOPTX. Also that it's a modest CRT which doesn't need high power deflection or much EHT.

As you reduce the number of lines, stationary images do tend to look grim. Moving pictures are another matter, as Don McLean showed in his restoration of Baird's 30 line recordings.

[Murphyv310]

Thanks Jeffrey.
I've just been looking at the tvdawn website (first I've seen it). Very interesting indeed. I knew about Baird's recordings onto 78 RPM discs but didn't realise there were any surviving discs.
Pity that the CD on TV Dawn is no longer available. Would also be nice to be able to have some old material to "play around with".