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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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9th Nov 2020, 9:57 pm | #41 | ||
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: Ideas needed to build a new 'old TV'
Quote:
Quote:
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Al |
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27th Nov 2020, 10:41 am | #42 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
A bit of progress, not much, but some. I have to decide on which CRT method of doing video modulation I am going to use, cathode or grid?
So I am going to put down my thoughts here as a way of getting feedback, and basically trying to get it correct in my grey matter. WRT Volts, the grid is negative to the cathode, so positive going video (-sync) will brighten the screen on video peaks. Negative going video (+sync) applied to the cathode will brighten the screen on negative peaks. At this point I am working on using the grid for video input and varying the cathode to provide fixed brightness. Not knowing how much voltage swing I need from black to white I am making an assumption of 50 Volts maximum. The plan using a DG7-5 CRT is to have the final anode at +HT of 230 Volts, which means that the cathode is down at around -600 Volts, this as it is relatively easy to use a voltage doubler from the mains transformer secondary to provide this negative volts using the normal HT to provide the 800 to 900 Volts required for the tube. It also means that the deflection plates are within the normal HT range approx 200 Volts. The down side is a separate 6.3 Volt heater winding for the CRT. I have issues which I am not getting through, one is DC restoration of the video as it has to be in the -600 Volt area, the second frame flyback suppression, using the screen grid from the frame miller timebase as a blanking pulse to drive the CRT grid when that is the video input? Anyway this is the circuit diagram to date. personnalTV.pdf Adrian Also on GVR. |
6th Dec 2020, 6:25 pm | #43 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
The IF section build can be found on GVR
OK a bit of an update, progress is slow as I work things through in my head, but within the recent CRT's I got was what I believed to be a 2AP1 tube, with a loose base that fell off whilst handling. So after spending some time with it I thought I would try and see if I could use it. I am using grid modulation and varying the cathode for brightness, there is quite a low allowed voltage difference between Cathode and Heater on this tube so I had to use a separate 6 volt transformer for the heaters and allow it to float or connect one side of the Heater to Cathode. This is the death trap for the unwary at the moment. It is displaying the test card from Hedghog, I can not focus it, the focus voltage being done for the DG7-5 not this tube, so either I modify the blue box on the back or fit the other tube. I had major issues with hum bars and trying to find where they came from, in the end, it was a mixture of EHT ripple and heater to cathode ripple both sorted by caps to ground. I hope to make things a bit better later tonight or tomorrow, My caps between the timebases at plates are at their very limit, so I need to find some 0.1uF at 1 or 1.5 KV. Adrian Last edited by AdrianH; 6th Dec 2020 at 6:33 pm. |
8th Dec 2020, 5:53 pm | #44 |
Octode
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,989
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Re: Ideas needed to build a new 'old TV'
liking it very much so far.
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Stephen _________"It`s only an old telly" ___ |
8th Dec 2020, 6:12 pm | #45 | |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,831
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Re: Ideas needed to build a new 'old TV'
Quote:
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A digital radio is the latest thing, but a vintage wireless is forever.. |
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9th Dec 2020, 1:17 am | #46 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
Did a bit more to the temp chassis today, I was wary of the way I had the CRT mounted so turned a nylon tube, mounting it and the CRT base to the wooden upright, fitting the tube and sliding felt between the neck and tube to add support.
It should be mounted in a metal shield etc, but not having one this is my alternative. Also a few component changes to the filed timebase gave me a bit more output, and equal push pull outputs. I know there is a slight curve to the frame output but not bad. You have pm Steve. Adrian |
20th Dec 2020, 8:02 pm | #47 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
An update to this today using the EHT generator and one of the other CRT's I have.
People may wonder I have some form of death wish, but honestly I do not, I just work in a hap-hazard way with wires all over the place. So I have the transformer PSU driving the make shift TV as it is, the small DG7-5 CRT is pulled from it's socket and wires soldered to the back of the socket going to another socket for a 5 inch CRT. The EHT generator is powered by a 12 Volt buck to supply 250 Volt HT and 6.3 V for heaters. That is powered by my small bench PSU bottom left. The DVM is monitoring the EHT and the final should be 20 x reading. I am trying a '5EP1'. This is a CRT with post acceleration, I thought I would try a situation where I am still using the voltages for the DG7-5 on the CRT but have approx 2000 Volts plus on the final anode. As I am using grid modulation and varying the cathode for brightness then the brightness control can effect the focus etc. I was surprised to find it did actually work OK with minimal tweaks to the Knobs. The final EHT when playing was at 2400 Volts. I am over scanning the height by quite a bit so need to include a height control, looking with my eyes direct at the screen I can just make out the 2MHz grating, so not so bad after all. It shows to me I can take the TV a bit further. I need to get hold of some better transformers as I need more heater current as I am very close to the limit for this one which is why the EHT unit is on a separate supply. I also need to find a suitable adhesive that is thin enough to poor into the CRT base that will re-stick it, I hate the prospect of un soldering the CRT base cleaning and then sticking it back on with araldite, I will ending breaking wires off doing it yet. Adrian |
28th Jan 2021, 11:22 pm | #48 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
I re-boxed the 'TV' over the previous few days and got it working today with the 5 inch 5CP1 . Think I need to change a few values on the A1 and A2 electrodes to remove a bit or barrelling on the picture.
https://youtu.be/md1DwCDHfzI All fun. Adrian |
29th Jan 2021, 10:47 am | #49 |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,274
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Re: Ideas needed to build a new 'old TV'
Nice linear scans.
Peter |
29th Jan 2021, 11:48 pm | #50 |
Octode
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
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Re: Ideas needed to build a new 'old TV'
Hi Adrian,
I'm very impressed with the picture on the Youtube video - they really are very linear scans. A huge amount of work to achieve and its been interesting following your progress. Well done! Cheers Nick |
30th Jan 2021, 12:05 am | #51 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
Well thanks for the comments Peter and Nick appreciated.
It has been sort of fun and sort of frustrating at times. I need to figure some sort of sound IF and get the response reasonably sharp for the audio around 50KHz, that is just a guess as to what it could be. May even try using some 5840 miniature Pentodes I have somewhere and an existing small valve audio amp. Also need a better heater supply some how. But the next thing for the box is a mask for the CRT, some holes for ventilation and a side cover, it is all something to do. Adrian |
30th Jan 2021, 12:07 am | #52 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
Just a thought on the general subject, to think this was popular thing to do late 40's to early 50's.
Adrian |
1st Feb 2021, 6:57 pm | #53 |
Hexode
Join Date: Jul 2004
Location: Paris, France
Posts: 350
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Re: Ideas needed to build a new 'old TV'
Hi to all,
@AdrianH : great achievement,Bravo ! Just for the fun of it, read about a similar endeavour by two French guys, Frederic A. & Pierre G. on their web site. A Miniature CRT Monitor. - All tube design - Every important section (Scanning, Video Amplication, Sync, Power supply) is studied in fine detail with an analysis of the Pro's & Con's of each design. - Loads of Scope photos Link is via Google translate Fr to English : https://translate.google.com/transla...pouces-01.html Also a lot of vintage radio projects on the main site Home page : http://www.cfp-radio.com/ Sample off-screen photo of the finished monitor (see below) Best Regards jhalphen Last edited by jhalphen; 1st Feb 2021 at 7:10 pm. |
2nd Feb 2021, 1:26 am | #54 |
Heptode
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 664
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Re: Ideas needed to build a new 'old TV'
I believe there were some articles in "Radio-TV Experimenter" magazine, "Radio News" magazine, or "Electronics World" magazine back in the 50's-70's with articles on how to turn a scope into a tv set. I do remember reading 1-2 articles on doing that. IIRC one used a PPI surplus indicator scope.
You might try looking the info up in your libraries "Readers Guide to Periolodical (sp) Literature for articles on conversion. HTH |
2nd Feb 2021, 3:08 pm | #55 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: Ideas needed to build a new 'old TV'
Quote:
Hi Adrian, Neat project and fantastic results. I hope you can find more video with the right aspect ratio for your set. Keep us posted! Cheers, Al
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Al |
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2nd Feb 2021, 4:00 pm | #56 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
@jhalphen
I have watched your videos thanks. It is good to see that others are still building and playing with valves and not just building audio amps for guitars. Have since come across valve logic circuits, a few doing TV's, one gentleman from Malaysia making his own scan coils (transistorised) for old RADAR tubes. Another doing logic circuits in valves etc, goes to show that there is good interest out there. @FrankB; I am probably finding too many articles from the era, it was, I believe when there was a major expansion in electronics to the common person, surplus military equipment was hitting the market and magazines were expanding to serve the curious minds giving many the opportunity to take part. @Al I am slowing getting some simple videos, Interludes, ' the potters Wheel', 'The kitten' 'Your Town'. These are the type of thing I like. There was one I seem to remember about the restoration of an old car, and painted by the owner and a young girl with a hoover! Not sure if that would be good on the green screen as it was a colour one. But some f the other Interludes or Engineering videos would be nice to get hold of. More searching some time is needed. Adrian |
3rd Feb 2021, 1:20 am | #57 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,713
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Re: Ideas needed to build a new 'old TV'
Quote:
https://youtu.be/S2lVR59V1bo?t=988
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3rd Feb 2021, 1:26 am | #58 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
Thanks I would have between the ages of 4 and 14 with that.
Adrian |
18th Feb 2021, 6:56 pm | #59 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
I built a simple sound IF board to add to the TV, two EF91 Mil type valves and EB91 equiv. Used an external audio amp as that is not part of the set yet.
Youtube video here https://youtu.be/UHnmOmn_gPw I seem to have picked up a copyright infringement for the Potters Wheel soundtrack, so I will have to come up with some suitable 'program' to play on my TV's if I do future videos. Adrian |
16th Apr 2021, 2:42 pm | #60 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
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Re: Ideas needed to build a new 'old TV'
Just an update as the TV does still get played with and bits added from time to time.
One of the things i was struggling with was heater current, I had reached the end of the transformers rating (ex surplus from here). I had approached a couple of transformer winders in the UK to see if they would do a custom build for me. They basically said no it would be to expensive and generally would not leave the decision to me what is expensive or not, i.e. I would not get a response or quote from them. So I bought a transformer for a guitar amp, which was way OTT for what I wanted and still not used it. When the transformer arrived it had another makers label attached. So another email sent asking the question about a transformer of the following: - UK Mains 240 Volt input, with full isolation to: 5 Volt heater at 2 Amps. 6.3 Volt heaters at 6 Amps 250 - 0 - 250 Volts at 200 mA. Fully shrouded with connecting wires. If my maths is correct this is close to 100VA. I had a quote back that I was happy with, even when I added the delivery charge and VAT I still thought reasonable. Not sure about giving details out here so i will not. It arrived and replaced the existing transformer on the PSU, I added the sound IF board added to the box and all tested OK. So the next thing I need to add before I can call this project sort of 'finished' is a single ended audio amp and speaker. Planning on using an ECL80 as I seem to have one, hoping that will be plenty for the small box to give sound. I need to find a small SE output transformer for it and then will take it from there. Adrian |