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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 31st Jul 2008, 11:23 pm   #1
mark pirate
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Default 405 from vhs?

Hi all, i am just at the begining of my first serious tv restoration (1950 bush tv22) & will have to wait a bit before i can afford an aurora, but have heard that one can use an old vhs machine to play 405 line tapes (i own several early vhs machines) can anyone tell me how to do this?
Cheers
Mark
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Old 31st Jul 2008, 11:37 pm   #2
Steve_P
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Default Re: 405 from vhs?

The early VHS machines will do this just fine. Better than later ones actually.

https://www.vintage-radio.net/forum/...hlight=405+VHS

Actually, because there are less lines on the picture and the frame is still 50Hz, they will look better on 405 than 625. Switch to B+W if there is a switch available on the back.

Just build a 405 Modulator. Job done.

Or, if you're clever, you could try Kat's method. It's amazing what a PC can do once it's rid of Windows!

http://www.g1jbg.co.uk/fothtv.htm

Cheers,

Steve P.
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Old 1st Aug 2008, 12:11 am   #3
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Default Re: 405 from vhs?

Hi Mark,

TV22 eh? Splendid, we'll look forward to seeing this project.
405 from VHS. Before you get technical, the first thing you'll need of course is some decent 405 line VHS recordings, they do exist and here is probably the place to ask if you havent any already.

As per machines, what Steve says is right, almost any working video will do, I know people specify the older machines, but to be honest any i've tried have been ok, even high end models.

Do a search here on modulators and you're all set

Good luck!

Regards
Stu
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Old 1st Aug 2008, 12:27 am   #4
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Default Re: 405 from vhs?

Remember that on 405, the VHS player won't fill in the 'correct bit of line' when correcting dropout errors on the tape, since it will assume the picture lines repeat every 64 μS (microseconds) of 625, not the 98 μS as is the case for 405.

This means that despite their excellent picture definition, some tapes may cause fleeting 'liney' interference from time to time. However, if you pretend it is 'ignition interference' this can even add to the authentic 405-line Band I experience!

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Old 1st Aug 2008, 6:54 am   #5
wiwior
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Default Re: 405 from vhs?

Hello,

It works so very well with of the other one video systems such betamax or video 2000. I prefer using betamax rather than vhs for 441 405. In fact I test a lot of video system recorder vhs, betamax, v2000 vcr for public and old umatic and open real professionnal systems.

When I make test in 819 I prefer to use betamax and umatic.

You can also transform your television set to 625 lines with some adapatation but it is true that it is more interesting to let them work in their chalk-lining of origin.

I often have on this subject of long discussed the French forum with my television sets 819 lines or few persons see the interest not to transform them 625lignes there.

wifrid
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Old 1st Aug 2008, 3:36 pm   #6
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Default Re: 405 from vhs?

True, but I wouldn't want to modify a set as this isn't keeping originality (and apart from that, we want to bring back the whole experience of 405-line telly .. 625 on a Bush TV22 just doesn't seem right at all )

I know you feel the same from what you have said about your discussions on the other forum

Does Betamax give a significantly better picture than VHS? Also worth asking .. is the head switching point an issue with 405-line VHS?

I haven't tried any recordings myself yet, but may well do tonight. First off the pile of VCRs will be a newish LG machine, will report back (or may be better to start a new thread for test results from various machines?)


Cheers,
BG
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Old 1st Aug 2008, 3:58 pm   #7
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Default Re: 405 from vhs?

If it does not check on line frequency as well as frame, it will work.

Line frequency is different on 405 of course. This is what causes the problem with some machines. Be interesting to know which do and which don't record 405.

As far as I know, Betamax and V2000 are the same. I wonder about N1500, SVR and N1700 formats.

Cheers,

Steve P.
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Old 1st Aug 2008, 5:50 pm   #8
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Default Re: 405 from vhs?

Hi.
I make up lots of tapes on VHS and have also in the past done it on Beta, there's not a lot of difference in quality both will resolve the last frequency gratings on test card C.
Where you will have the problem is as already stated with the DOC, if on your playback video you get a ghost at about a third of the picture the DOC has to be disabled, easy in an older machine often a twiddle of the DOC level control will do, or remove the video input to the DOC. Modern machines are more difficult but some dont display the ghost.
Remember vcr's are intended for the 625 line timing of 64us so some machines see the longer timing as tape noise and try to add lines of course at the wrong time constant. It may be possible to alter the delay line to work on 405 but good tapes shouldn't have too much drop out.
Trevor
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Old 1st Aug 2008, 11:01 pm   #9
mark pirate
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Default Re: 405 from vhs?

Many thanks to everyone, have now read all the threads about modulators
will attempt to build one inbetween restoring my tv22, have also been reading about the restoration of a tv22 on the radiocraft website, i intend to do a top job on this set, have been after one for a while now, then 2 come along within days! set No2 is in better condition, complete with instructions & guarantee (it did cost more though!)
so this will be the set i will restore, if i dont have to rob too many bits from set 1 this will also get restored.
looks like i will be confined to my workshop for the winter months

Mark
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Old 2nd Aug 2008, 4:14 am   #10
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Default Re: 405 from vhs?

Some panasonic VHS recorders used a ccd (bucket brigade) delay in their drop out compensator. It is clocked from memory ay 1024 times line rate 16MHz. if the clock rate is reduced to 10.368MHz. the dropout comp should work correctly on a 405 line signal. I don't remember the models that employed the ccd chip but I am sure somebody on this forum will know and be kind enough to post to this forum. I have used the chips in an early attempt to standards convert but cannot find the details or the converter. If I find the details I will post.
My own observations indicate that it would be well worth the trouble have a good doc in a 405 line vcr if for no better reason than ageing tapes need d.o. correction
in order to make a reasonable copy.
Victor.
P.S. The chip is a standard 14 0r 16 pin dil package and very easy to use.
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