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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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29th Jun 2021, 7:13 pm | #1 |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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AV on a 405 line set?
Hi all
I just had a thought, how easy would it be to inject composite video into a 405 line TV, bypassing the tuner. Would it even be possible due to the difference in resolutions from the TV and the source (like a STB for example.) It's not something I'd plan to do but was just curious if it's possible and if so the obstacles that'd get in the way. Thanks '77 |
29th Jun 2021, 7:21 pm | #2 |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,274
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Re: AV on a 405 line set?
If you are thinking of AC/DC TVs you'd be better just to build a modulator and connect via the aerial input.
Peter |
29th Jun 2021, 7:30 pm | #3 |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
I personally would go the aerial route, as it makes the most sense. I was more curious on the technical side of it and it's possibilities. I think I'm thinking more of the 405 line system itself than any particular sets
'77 |
29th Jun 2021, 9:39 pm | #4 |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
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Re: AV on a 405 line set?
Not a difficult job to convert most sets to composite input but needs an isolation TX. Don't quite understand what you attempting to feed in, no STBs or DVD with 405 lines. Some line oscillators might just reach 625 with a bit of a twiddle or a couple of component changes but the LOPT won't be happy running at that frequency.
Last edited by jayceebee; 29th Jun 2021 at 9:59 pm. Reason: more info |
29th Jun 2021, 10:26 pm | #5 |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
It's not something I plan on actually putting into practice, it was more just a curiosity of if it was possible or not, as I know 625 line sets can be converted but didn't know about 405 line sets. Didn't know if composite output on a set resolution or was just the direct video signal itself either so that's something learnt
I did think the oscillators would've been adjusted myself, but wondered if it'd have been just as simple as that or had other technical hurdles to pass '77 |
29th Jun 2021, 10:42 pm | #6 |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
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Re: AV on a 405 line set?
Unless you're going way back most video output stages would handle the 625 video bandwidth without too many issues. A cable TV company called Rediffusion modified lots of their cable 405 only sets to 405/625 operation but I suspect all will have needed an upgraded LOPT.
Actually a lot of people modified sets to baseband video in and out recording the 405 video on to VHS recorders then playing them back. This was before standard converters like the Aurora became affordable. Recorders like the Ferguson 3V29/30 could record 405 no problem but some issues could be seen on playback due to the 64uS drop out compensation. Last edited by jayceebee; 29th Jun 2021 at 10:56 pm. Reason: More info |
29th Jun 2021, 11:06 pm | #7 |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
Funny you should mention Rediffusion as it's my Rediffusion (MK7, c1963) that made me think of all this. It's an aerial set but is missing the tuner, and so it brought up the idea, not that I plan to do it as I'd rather it was running on original circuitry.
Thats interesting about recording 405 line footage onto tape, I have actually read about it briefly before. Also funny you should mention the 3V29 as I've got one of those too! Maybe when I get a little more advanced I can try record 405 line to VHS with it and see for myself. It's an interesting subject really '77 |
30th Jun 2021, 8:43 am | #8 |
Heptode
Join Date: Feb 2007
Location: West London, UK.
Posts: 867
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Re: AV on a 405 line set?
I did not think there were any Rediffusion MK7.s left. I worked on them at Rediffusion
in the 1960's. Not my favorite, set especially the aerial version. So pleased you have saved one. Could you not get a different tuner to work and then feed a signal in. John |
30th Jun 2021, 8:58 am | #9 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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Re: AV on a 405 line set?
When I did the initial tests with the PC graphics card, it was before I had built an RF modulator. I simply applied the baseband +ve video directly onto the grid of the video output valve.
I think I mention it here. https://youtu.be/T2oNculjoQc PS it's essential to use a mains isolation transformer.
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30th Jun 2021, 11:02 am | #10 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,130
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Re: AV on a 405 line set?
As long as the VCR doesn't attempt anything clever, such as the aforementioned dropout compensation, it is indifferent to what is recorded within a frame of video, which it records as a single helically-recorded stripe of 20mS (the frame period of both 625 and 405). Of course, once it replaces a 64μS line that it determines has dropped out, this will fail to match the line structure of 405 lines and cause various glitches.
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30th Jun 2021, 1:23 pm | #11 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,820
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Re: AV on a 405 line set?
As has been said, it can be done, I did it during the restoration of my Ekco TMB272, which is a mains isolated 405 only TV, I wouldn’t try it on anything that wasn’t isolated. I used the composite output of the Aurora standards converter, fed via a capacitor onto the grid of the video amplifier valve, the picture was actually pretty good! I was trying it as the tuner/IF stages were not letting anything through at the time.
Regards Lloyd |
30th Jun 2021, 2:36 pm | #12 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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Re: AV on a 405 line set?
Quote:
https://youtu.be/P8MHUcEM0ts Mind you, it may be a different story if the tape is played back on a different machine (I must try that sometime).
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1st Jul 2021, 7:06 pm | #13 | |||||
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
Quote:
Quote:
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Does anyone have an example of what the glitches look like? Sounds interesting Quote:
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(Sorry for the late replies, had poor internet for a while) Thanks for the replies '77 |
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1st Jul 2021, 7:19 pm | #14 |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,274
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Re: AV on a 405 line set?
I don't know the set but I'd have thought it unlikely that a 1963 Redifusion would have a mains transformer.
Peter |
1st Jul 2021, 9:43 pm | #15 | |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,274
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Re: AV on a 405 line set?
Quote:
I recorded a short piece of 405 line VHS. I am only playing it back on my Panasonic NV-FS90 and its drop out compensator causes a slight ghosting of the image which you should ignore and just concentrate on the actual dropped lines which are simply occasional horizontal flashes. https://youtu.be/Z46N7imx-O0 Peter |
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1st Jul 2021, 9:48 pm | #16 |
Heptode
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 732
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Re: AV on a 405 line set?
That is not bad at all Peter.
I was expecting to see something a lot worse. Frank
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1st Jul 2021, 9:55 pm | #17 |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,274
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Re: AV on a 405 line set?
Hi Frank,
Yes, the VHS video bandwidth shows up quite well at 405 line speeds. I'm playing it on my Sony 9-90 which on VHF suffers from a lack of DC restoration but I just used the UHF output of the VHS machine because the 9-90 can play UHF 405 with much better DC response. Peter |
1st Jul 2021, 10:07 pm | #18 | |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
Quote:
I agree with Frank.C and have to say it's much better than I expected. I was expecting a mess but that looks perfectly watchable to me, and I expect it looks better in person too? Thank you for uploading that video, that was interesting to see, and see it performed so well at that '77 |
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1st Jul 2021, 10:09 pm | #19 |
Octode
Join Date: Jun 2018
Location: Essex, UK.
Posts: 1,307
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Re: AV on a 405 line set?
Forgot the photos
Oops! (I was surprised at how big the cabinet is for a 19" set. That's it sitting on top of a 26" set for a size comparison) |
1st Jul 2021, 10:18 pm | #20 |
Nonode
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 2,820
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Re: AV on a 405 line set?
I’d say that’s not mains isolated, just going by the large green dropper resistor, those transformers are too small to be mains isolating types, more likely one is a choke and the other could be audio output or frame output transformers. Safest to assume it’s live chassis until proven otherwise!
Regards Lloyd |