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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 5th May 2008, 11:27 pm   #1
Mullard
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Default American TV Conversion

Amongst other things I collect micro TVs from around the 1980's. These are monochrome, have CRTs and solid state electronics. CRTs are 2 to 3 inches and include the notorious Sinclair TVs. I am currently working on a Sinclair MTV1. There is a very good web site where information about this type of set can be found at http://www.taschenfernseher.de/e-tube.htm.
A number of interesting miniature sets were produced for the US market and these are available in good condition at a good price, even taking into account the shipping costs. I have recently obtained a Realistic 16-103 (also sold as Emerson VR-22, Normende TR101, Orion TVR-7120, TMK 717, Unisonic XL-990, or Broksonic CIRT-2097T in different liveries) and I am planning to convert it (with minimal modifications) to work on the UK standard.
The video is simple as this can (and has) been done by adjusting line frequency, frame frequency, and vertical amplitude. There seems to be no adverse effects.
The real work is going to be on the sound, as the US system uses a 4.5Mhz sound carrier rather than the UK 6Mhz. I was wondering if anyone has tried to do this and if they could share their experiences. I was thinking of trying to retune the 4.5Mhz IFTs to 6Mhz, but it seems like a large shift. I am keen not to replace anything more than I need to, as I want to retain as much originality as possible.
All thoughts welcome.
John
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Old 6th May 2008, 9:01 pm   #2
yagosaga
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Default Re: American TV Conversion

Hello,

the conversion from U.S. to U.K. standard does not only affect the different sound I.F. but also the I.F. bandwidth. The video bandwidth in U.S. tv sets is limited to 4 MHz, all frequencies above are cut. If you adjust an U.S. for the exact British sound I.F., you will probably listening to a noisy sound. You have to readjust all I.F. stages. This is my experience which I had with my first attempt of conversion (for German 5.5 MHz sound I.F.). After that I leave the U.S. tvs as they are, and I use an U.S. R.F. modulator for channel three or four.

Kind regards,
Eckhard
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Old 7th May 2008, 2:31 pm   #3
jhalphen
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Default Re: American TV Conversion

Hello to All,

Hi! Mullard,

I'm also a micro-TV fan (the entire Panasonic TR-series) Sinclair, + countless LCDs, etc.

Here's my solution:
I live in France which has a really weird Over The Air TV system, so collecting any foreign tv is a problem for me, nothing works here!

For NTSC: PAL or DVT-T source --> digital standards Converter --> US Transmitters (2x)
PAL B/G: PAL or DVB-T source --> PAL B/G transmitter
PAL-I (UK) same setup --> for Sinclair TVs mainly
SECAM L: PAL or DVB-T source --> high quality PAL to SECAM transcoder --> L Transmitter.

I used to build my transmitters, but now i purchase this Greek product:

http://www.aspisys.com/tvpll.htm

It can be programmed for any of the standards above, it put out 100mW with quasi-broadcast picture quality. OK, it's not a Vestigial Sideband true Broadcast unit, but if you choose your channel(s) well i.e. don't interfere with a "legit" signal, no one will notice.

I tend to repackage each TX in an aluminium box to keep RF fields inside the box & ensure adequate cooling for the +5V & +12V IC regulators.

I live in town, have PAL B/G + NTSC + FM radiating 12 hours a day and i've never run into trouble. In many Euro-countries, VHF Band III is quasi-abandoned and pretty much free.
Been doing this for at least 10 years, first in B/G then added the other systems as my collection grew. As a bonus, coverage & S/N is much better in VHF, why, for instance, the UK & France moved all TV to UHF is still a mystery for me.

With this solution, you can use your little sets freely throughout your house off their whip antennas & amaze your friends, you do not have to modify miniaturized electronics and you do not risk tripping over tens of coaxial feeds from modulators.

Works for me, thought it would be nice to share...

Best Regards

jhalphen
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Old 7th May 2008, 3:46 pm   #4
Mullard
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Default Re: American TV Conversion

Many thanks for the suggestions. The current set I am converting (Realistic 16-103) has no crystals or ceramic filters but 1 sound IF transformer and 1 IF coil. I have the service manual for the Emerson VR-22, which is the same internally. As yet I have not had time to try retuning these, but I suspect as suggested above that this will require a change to the caps as well as the tuning slugs. The sound IF uses an AN6730 IC and the only datasheet I can find is in a mixture of English and Japanese and only mentions 4.5MHz. I do not know how it will respond at 6MHz, but this is not so different so I suspect it will be adequate. Retuning the video IF is not currently an option as I don't have a sweep/marker generator. Perhaps I should look on ebay.
The set is very small and therefore very portable. Any sound quality issues may be disguised by the limited quality of the audio amp and loudspeaker.
I would like it to stay portable while we still have analogue transmissions, and then I will probably do something like jhalphen suggests to run all the portables. I might also get a US modulator as this seems like a quick route to get sets working.
One other thought I did have, and that is replacing the coils with 6MHz ceramic filters. Not something I have any knowledge about, but I might do some research.

Happy days.

John
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Old 8th May 2008, 11:23 am   #5
jhalphen
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Default Re: American TV Conversion

Hi John,

I've looked through my scanned schematics and i have the Brandt TR-101, which is once again yet another rebadged version of the Orion TVR-7120, Emerson, Nordmende, ISP, ...

What is interesting is that this made for France model has EU-UK-Fr switchable sound section.

Euro models have EU-UK-USA switchable audio, the US model has only one position, US.

I have the complete manual with parts list which should make your job much easier. Give me your E-Mail address & i will send it to you. These are high quality scans which are much too defined to pass on the forum.

Best Regards

jhalphen
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Old 16th May 2008, 11:52 pm   #6
jhalphen
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Default Re: American TV Conversion

Good Day Gentlemen,

Epilogue: Service manual/schematics sent (free) to Mullard.

He will be able to modify his US TV for UK sound operation.

end of thread

Best Regards

jhalphen
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Old 18th May 2008, 10:54 am   #7
Mullard
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Default Re: American TV Conversion

I decided yesterday to have a go at getting the sound working and decided to try changing the caps across the IFTs to shift them up from 4.5 to 6 MHz (see attached circuit T301 and T302). On opening the case, I decided first to try retuning the cores. I wound them both well out and powered up. Tweaking the first IFT, with a station tuned in, I managed to get quiet sound but even with the 2nd IFT core right out I couldn't get up to 6 MHz. Then I had an idea, a brass tuning slug would lower the inductance. I made up a brass slug from a 3.5mm brass screw and cut a slot in one end. This allowed me to get to 6 MHz and the sound quality was good and strong. I was surprised how well it worked considering that I had done nothing to open up the video IF bandwidth. In fact it performs as well as any of my other sets. There seems little point in pulling the set apart and changing components if it works well by adjustment.
So in the end I didn't really do too much. Thanks to jhalphen I have the service data for the multi-standard version and I notice the board is tracked for that version. The multi-standard version uses varicap diodes and trimmer pots to allow the sound IF to be switched between 4.5, 5.5 and 6 MHz . I will certainly be looking out for a multi standard version of the set and will probably buy a few more US portable sets as well.
Thank you to those who have responded. I hope it has been of some interest.

John
Attached Files
File Type: pdf Realistic 16-103 IF amp.pdf (238.1 KB, 202 views)
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