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Rediffusion Mk1 CU2213.

 
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Re: Rediffusion Mk1 CU2213.

Post by Till Eulenspiegel » Sun Oct 18, 2015 11:52 am

Hi Gary,
I'm sure there are some orange convergence pots in my ever growing stock of CTV parts.
The Mark 1 is a magnificent piece of over engineering. Ever tried to lift the 26" version? It's heavy.

Till Eulenspiegel.

 
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Re: Rediffusion Mk1 CU2213.

Post by Rebel Rafter » Sun Oct 18, 2015 8:42 pm

Hi, folks, RR here. It seems to me the " telebox" is just a tuner and IF strip feeding a modulator, and it will only work with the now non-existent analogue broadcast so isn't it possible to make a modulator that works at 8.9 MHz? surely that's all you need, you might have to wind your own coils for it and it would most likely have to have a floating output winding or balanced output and as I remember the sound goes in at baseband and strong enough to drive the speaker direct on the same pair of wires, so that could be a bit of a challenge for someone. If you find another spare SF receiver board for a MK1 or some other "wired" set you might be able to use some of the coils from that, but it's a bit beyond me, I'm no designer but I know the basic requirements. If you use a telebox you would have to use a UHF modulator to feed it first and lose signal quality or alternatively you could tap into the telebox's own modulator section, that way you wouldn't need a UHF modulator, unless the telebox has a baseband input. RR.

 
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Re: Rediffusion Mk1 CU2213.

Post by Till Eulenspiegel » Sun Oct 18, 2015 9:02 pm

Here's an idea. To make a 8.95Mhz modulator you can either modify the David Looser design which appeared in the August? 1984 Practical Television magazine or the ETF 405 line system modulator. I'd reckon the latter is the better choice because a pre-made PCB is available. The circuit will have to be modified for negative modulation which in fact what the Motorola MC1374 was designed for. The oscillator coil will have to be modified of course. More turns for 8.95Mhz.
http://www.earlytelevision.org/405_modulator.html
A small 3watt audio amplifier will drive the speaker direct.

Till Eulenspiegel.

 
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Re: Rediffusion Mk1 CU2213.

Post by ntscuser » Sun Oct 18, 2015 11:17 pm

Till Eulenspiegel wrote:The circuit will have to be modified for negative modulation which in fact what the Motorola MC1374 was designed for.


The American 441-line system was also negative modulation was it not?

 
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Re: Rediffusion Mk1 CU2213.

Post by Till Eulenspiegel » Mon Oct 19, 2015 12:28 am

ntscuser wrote:
The American 441-line system was also negative modulation was it not?


Indeed it was. Channel width was 6Mhz the same as the 525/60 line standard so it could be said the latter system could have benefitted from a wider channel width. The active picture part of a scanning line is almost the same as the 625/50 standard.
441/60 line system sound was amplitude modulation and was replaced in 1941 by FM along with the introduction of the 525/60 standard.

Till Eulenspiegel.

 
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Re: Rediffusion Mk1 CU2213.

Post by freya » Mon Oct 19, 2015 8:51 am

I presume this is the type of rediffusion converter box you are referring to ?
Attachments
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Re: Rediffusion Mk1 CU2213.

Post by crustytv » Mon Oct 19, 2015 8:55 am

Yep that's the box I'm looking for

 
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Re: Rediffusion Mk1 CU2213.

Post by freya » Mon Oct 19, 2015 9:28 am

Just opened it up, two screened modulator boxes have been removed. A third one remains.
I think I have another converter somewhere, will keep an eye out for it.

 
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Re: Rediffusion Mk1 CU2213.

Post by crustytv » Mon Oct 19, 2015 10:06 am

Sadly that was the fate most these boxes faced, they were butchered used to make 405 Modulators. Can't blame folk though as they were pretty much redundant hardware and at least that way they served a second purpose. I have my fingers crossed one may turn up eventually.

 
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Re: Rediffusion Mk1 CU2213.

Post by Cathovisor » Mon Oct 19, 2015 11:44 am

CrustyTV wrote:Sadly that was the fate most these boxes faced, they were butchered used to make 405 Modulators.

Mmm, not really; just as many were used to make TV sound receivers for hi-fi systems and the like. I remember Field Electric (who were opposite Elstree and Borehamwood railway station) selling them amongst others.

 
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Re: Rediffusion Mk1 CU2213.

Post by crustytv » Mon Oct 19, 2015 11:52 am

I should have said "many" not "most" as obviously the numbers of people interested in 405 modulators would be a minority compared to TV sound receivers for hi-fi. Interesting to know the other uses they were put to so thanks for filling in the gap. Whatever the use few survive today, I've not seen one in the six years I've been on the scene but that is only a tiny fraction of time in the grand scheme of this hobby.

 
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Re: Rediffusion Mk1 CU2213.

Post by Cathovisor » Mon Oct 19, 2015 12:02 pm

...and let's not forget these things were being sold off thirty years ago; most will have headed for landfill. I wonder how many survived to be used with the Maplin NICAM decoder?

Have to say, I rather like David's idea of using the ETF modulator inside a rescued box that's lost its modulator...

 
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Re: Rediffusion Mk1 CU2213.

Post by malcscott » Mon Oct 19, 2015 12:49 pm

It is a good bet that i will have a couple of these frequency translators in my stores, Malc :bba

 
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Re: Rediffusion Mk1 CU2213.

Post by Till Eulenspiegel » Mon Oct 19, 2015 4:02 pm

Till Eulenspiegel wrote:Here's an idea. To make a 8.95Mhz modulator you can modify the David Looser design which appeared in the August? 1984 Practical Television magazine


It was in the October 1984 television Magazine. I'd use this one if you fancy recreating a 405 line cable service. However, there is no chance of a 405 only Rediffusion set ever turning up.

Till Eulenspiegel.

 
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1976 Rediffusion CH2213: MK1 Chassis

Post by crustytv » Mon Mar 21, 2016 4:59 pm

CrustyTV wrote:I have a wired chassis and intend to get it running so I have two examples of the MK1 in the collection. Though I need the Rediffusion Frequency translator box for this one.

Thanks to a visit from Mikey66 on Saturday I now have the cabinet for my wired MK1 :thumb

 
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Re: Rediffusion Mk1 CU2213.

Post by Katie Bush » Mon Mar 21, 2016 8:29 pm

Crusty TV wrote:I need the Rediffusion Frequency translator box for this one.


Hi Chris,

I don't really know how difficult it would be, but I was wondering if it might be possible to build a simplified translator? It would be a very interesting project, and I'm sure that if it's possible to build DIY standards converter, one of these should not be beyond the realms of possibility.

Marion

 
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Re: Rediffusion Mk1 CU2213.

Post by crustytv » Mon Mar 21, 2016 9:48 pm

malcscott wrote:It is a good bet that i will have a couple of these frequency translators in my stores, Malc :bba

Hi Malc,

Just wondering did you ever get a chance to check the inner most sacred places of your Tardis for a translator box? couldn't arf! use one now.

 
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Re: Rediffusion Mk1 CU2213.

Post by Terrykc » Wed Mar 23, 2016 12:47 pm

Chris, presumably you have a UHF feed for your other sets, so why not build a simple frequency translator to feed the Rediffusion set?

Take any available UHF tuner and feed its out put to a simple mixer together with a suitable local oscillator signal. This could be as simple as one transistor for each function or even a one transistor mixer/oscillator*.

As the area below 8.95MHz was occupied by the pair of 405-line signals, I'm assuming that the 625-line IF strip is upper sideband.

As the UHF tuner transposes the broadcast USB signal into a LSB IF one, we need to transpose this again by running the local oscillator 8.95MHz above the 39.5MHz IF - so 48.45MHz.  

Without the filtering of an IF strip, the tuner's IF output will be fairly broad so absolute accuracy won't be necessary but, if you don't have a frequency counter, you could set the oscillator frequency accurately by tuning the 2nd harmonic for 96.9MHz on a seasonably accurate FM radio.

If your tuner came out of a set using the continental 38.9MHz IF, again extremely high accuracy isn't needed but the precise oscillator frequency would be 47.85MHz. (2nd harmonic 95.7)

Add a suitable audio amp and PSU as required.

* A modified FM tuner mixer/oscillator, perhaps, with R-C coupled input and output (relying on the tuner output coil and TV IF input for these functions)

 
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Re: Rediffusion Mk1 CU2213.

Post by Till Eulenspiegel » Thu Mar 31, 2016 10:09 pm

Hi Chris,
During a clear out in the shop today I found the Rediffusion Telebox I used to use with my own build 405 line converter up to the close down of analogue TV.
You are most welcome to it.

Till Eulenspiegel.

 
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Re: Rediffusion Mk1 CU2213.

Post by crustytv » Fri Apr 01, 2016 11:49 am

pm sent

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