How to get a signal into a Rediffusion Durham

This set can only be used with the Rediffusion H/F system

Hi Malc, just to amuse me  could you let me know what sort of effort i would need to put in to create a signal source to get the set going?. cheers,neil.

Hi, if i could find a box would it be a simple matter to just put it back to it's original spec?. or are there any parts that cant be found anymore. thanks,neil.

When i worked on the Rediffusion MK1 test rig, video output from a Grungig FG5E pattern generator was fed into the S/F panel. This method could be done with the MK11 mono chassis which this Durham set uses. A circuit diagram will be needed to find the point of input. The only way to obtain audio is from an external source. I will have rake around for a cct, but i cant promise anything. Best of luck, Malc

Hi Neil,
When you mentioned that you had 'won' this set, I wondered how you were going to use it.
These sets were made for use with the Rediffusion cable network, now long gone. I remember this system from when I lived in Bristol in the early 1980s. Bristol had an extensive Rediffusion cable network, although it did not extend to the area where I lived. Homes which were wired for Rediffusion cable TV had a rotary switch, sometimes Bakelite or white plastic, on their wall or windowsill. This connected the desired audio and video signals from the network to the TV, by rotating the switch you could change channel. The set did not have its own tuner.
The Rediffusion cable network in Bristol carried BBC1, BBC2, ITV and some radio stations (BBC Radio Bristol was channel "C" on the Bakelite switch, I think.) When Channel 4 launched in 1982 there was a problem. The network wasn't designed for 4 TV channels! To overcome this, Rediffusion gave their subscribers a set-top box called a "Translator". This had a UHF tuner inside, and converted the terrestrial channels from "off-air" to Rediffusion cable format. Customers had to have a new UHF aerial installed, if they didn't already have one.
Later on, Rediffusion dropped all the terrestrial TV and radio channels from their cable network, which then carried premium Pay-TV services like MTV, CNN and Prem1ere (a movie channel.) Customers had to use the Translator box for terrestrial channels. Even later, they stopped using special sets. The 'pay' cable channels were fed into a UHF modulator 'brick' on the wall and fed into a normal TV aerial socket.

Now if you can find one of the old Rediffusion Translator boxes, your problem will be solved. Just plug it into the set and use it like a normal UHF analogue TV. The problem is that the Translator boxes are now quite rare. Some of them would have gone to landfill with the set when it died. Some were re-used for other purposes, as Jeffrey says, for making Band 1 modulators for 405 line TV. Another company modified and sold them as tuner boxes to convert computer monitors into televisions. They do still turn up occasionally - keep looking!
If all else fails, it should be possible to inject a composite video signal somewhere in the TV. The audio went more or less directly from the Rediffusion cable network into the speaker, via a matching transformer inside the set. There is therefore no audio amplifier or output stage inside the set. One interesting feature was that you could listen to the radio or TV sound with the set switched off. The sound was powered by the cable network. In the beginning, customers could just rent a speaker if they only wanted radio and not TV.

Malc might have the frequency info required but, as I recall, the HF system was centred on ~7MHz with one carrier above and one below (this was in two channel days, I haven't a clue how they added BBC2!). The carrier frequencies were carefully chosen so that the upper sidebands of the lower frequency carrier interleaved with the lower sidebands of the higher frequency carrier.

(France used a similar idea for squeezing their rather wide 819 line channels into the VHF bands, effectively swapping the sound a vision frequencies at transmitters to allow the same channel to be reused by transmitters that would have other wise have interfered with each other.

So, assuming an Aurora will be used for 405 line signal generation and set to Channel BI (45MHz vision), if this is mixed with suitable oscillator to give a beat at the correct frequency, the HF signal can be recreated.

Assume the HF carriers are 10MHz and 5MHz. The vision sidebands of Ch BI are below vision carrier so, a 50MHz oscillator will produce a 5MHz carrier with upper sidebands and a 35Mhz oscillator will produce a 10MHz carrier with lower sidebands.

Considering that the Aurora output is DSB, the 35MHz option woud probably be better ...

If Malc can come up with the all important frequency information, this rather crude, but simple, idea may well work as no filtering would be needed as the whole thing would be self contained.

Hi, i will search my spares dept at the weekend. I may have a couple of Rediffusion frequency translators in stock, Malc

From memory the crystal in the translator box modulator was about 8.5MHz ...

That figures ...

As far as I can find out, single channel (ie: pre ITV!) systems used 9.72MHz Upper Side Band signals to which were added 6.3MHz Lower Side Band signals for ITV.

Later, the interleaved system was introduced with 4.95MHz USB and 8.45MHz LSB carriers.

For 625 line working, these were changed to 5.4MHz USB and 8.3MHz LSB, then later changed again to 5.9MHz USB & 8.9MHz LSB, so you pays your money and you takes your choice but, as this is a colour set and, therefore, later, I'd guess at 8.9MHz ...

If an Aurora is being used for 405 line signals, my previous suggestion would work. As the Aurora is DSB, it doesn't matter whether the new local oscillator is above or below the Aurora's output so, for Channel 1, 45MHz ± 8.9MHz (36.1MHz or 53.9MHz). Just mix the two RF sources together and you should get an 8.9MHz source.

On the subject of Rediffusion, here's a story I heard a very long time ago ...

When Rediffusion were awarded the contract for the New Town at Basildon, they were warned that a licensed amateur, very active on 7MHz, lived within about 100m of their proposed head end site. However, they chose to ignore the warning which caused them considerable problems as 7MHz is, of course, slap bang in the middle of their distribution passband ...

The story may be apocryphal, of course ...

Hi Neil,
I've got a spare Rediffusion telebox. you are welcome to one. FOC, kostenlos. just the postal charges to pay.

Till Eulenspiegel.

That's brilliant  thanks again David. can you let me know the postal costs and your address etc and ill send you a cheque for the total. and also thanks to jeffrey,Malc for the info as well  much appreciated. cheers,neil.

Hi Neil,
I've sent you a PM.

Regards,
David.

I never really paid too much attention to it, but I seem to remember there was often a box advertised in Television magazine probably in the 80's or 90's called "The Amazing Telebox' which looked a bit similar to that Rediffusion box.
Anybody care to educate me on what that thing did or what was amazing about it?

Eddie

As I mentioned earlier, one company sold re-cycled Rediffusion cable TV converters for use as TV tuners - that's what "The Amazing Telebox" was. If you happened to have a CCTV or computer monitor that accepted composite video input, the Telebox could enable you to watch TV on it. Back then, this was a big deal. Of course, you could simply hook up a video recorder to your monitor and use it as a TV tuner, but then video recorders were expensive. So was a second TV. The telebox offered to convert a monitor into a TV for an attractive price. The low price was possible because it was reclaimed scrap from Rediffusion. I think it contained an audio amplifier and could drive a loudspeaker directly, useful if your monitor didn't have a speaker built-in. Other than that, nothing amazing really.

Hello all, Can someone let me know what equivalent transistors can be used to replace the TO1, SGS device that sits on the timebase panel(the one with the crinkly heatsink) as the legs have rusted off this one completely. thanks, neil.

Hi all, If possible can someone put up some service info for the set so i can get an idea what voltages etc to expect. thanks,neil.

Has the TO1 transistor got a part number on it?
Be careful when you take the heat-sink off as it may take the number with it.
It there enough of the leads left to get some readings from it so that we can tell what type it might be.

The large transistor is the frame o/p BLY48/2N3055. The small transistor is used in the regulator cct. It is a BFY52. Also replace the 15v zener next to it. Malc

Hi, I probably should have mentioned the numbers to start with. it's an SGS26839 UJ4545/1. im not sure which of the numbers is the actual part number so ive written it all down. and again i should have been a bit clearer with the location, it's between the large can and the heatsink and the blue lead that goes directly to the tube is close to it as well. thanks,neil.

Now it is Google time Have a look at this link. http://markhindes.easywebstore.co.uk/se ... m=SGS26839