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Old 3rd Oct 2014, 10:58 pm   #21
McMurdo
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Default Re: Thorn 2000

I was under the impression that there was some legislation involved regarding the sale of new TVs after a certain date which required them to be dual standard
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Old 4th Oct 2014, 3:04 am   #22
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Default Re: Thorn 2000

The Thorn 980 405-line chassis stayed in production until 1968 and was probably sold for a further year after that by which time 625-line only sets were available from most manufacturers so I don't see how that was possible?
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Old 5th Oct 2014, 9:58 am   #23
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Default Re: Thorn 2000

Hi there
I had a look at that picture of the Thorn 2000 "breadboard" as it was called - it looked like an explosion in a BT distribution box! How they managed a working set from that is amazing.
Incidentally, The Setmakers book says that ITT never intoduced a dual-standard colour which I'm sure Mikey would have something to say about, though there were very few made.
I might be wrong, but I imagine that the EHT multiplier was developed for the 2000 and when it was seen to be reliable was adopted by GEC for their dual-standard set. I suspect dire warnings about the stability of the EHT came from Mullard selling the PD500, something that never seemed to bother the GEC set. Of course Bush had the worst of both worlds with the CTV25 Mk3! It would have been interesting to see whether the Bush set would have worked reasonably well without the PD500. Considering the additional load on the quadrupler they fared reasonably well, which is more than the transformers did.
Steve - years ago I too had one of these fearsome Körtings with a duff 25kV overwind on the EHT transformer (GY501 rectifier, no shunt stabiliser, not unlike the B&O). I fabricated one from a G6 transformer which worked after a fashion but I never managed to cure a decoder fault.
Glyn
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Old 5th Oct 2014, 11:27 am   #24
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Default Re: Thorn 2000

The 980 was given away with Colour TVs at the end. The production line was moved to Baird's Bradford plant while I was there.
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Old 5th Oct 2014, 11:47 am   #25
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Default Re: Thorn 2000

I bought a 2000 when they 1st appeared. Back then as I recall we only had BBC2 available on 625 lines with some colour. Gradually BBC1 and ITV appeared on 625 lines.
I remember changing one of the 'special' square Texas transistors several times in the first year, all supplied Foc. One Saturday evening it failed again, so with nothing to lose, I tried a 2N3055 and it worked for many years before it failed.
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Old 5th Oct 2014, 11:52 am   #26
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Default Re: Thorn 2000

The first colour set we had was a 19" Thorn 2000. Got it from work (British Relay).

It ran well for quite a few years; we sold it to a neighbour when we acquired a G6
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Old 5th Oct 2014, 1:18 pm   #27
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Default Re: Thorn 2000

I got mine from a neighbour, in exchange for a new CTV cabinet I bought surplus to make a toy box. It had several faults none of which were serious.
Being in line of sight of Emley Moor, the aerial was a terminal screwdriver balanced between the socket and the lounge wall.
I now regret scrapping it after it's second replacement tube failed and replacements became difficult to find.
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Old 5th Oct 2014, 7:03 pm   #28
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Default Re: Thorn 2000

The BRC all valve colour set got a mention in the October 1966 issue of "Practical Television" when it was displayed with sets from other manufacturers at an exhibition. No photo of it unfortunately. Have any survived I wonder?

It was only nine months later (July 1967) when the same magazine featured an article on their all transistor colour sets. Quite an achievement!

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Old 6th Oct 2014, 11:30 am   #29
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Default Re: Thorn 2000

Back in 1970, a chap I worked with was extolling the virtues of CTV to me, and invited me up to his house one dinner time to see it. It was a Thorn 2000, and I just remember the scene of a large pool with PURPLE swans swimming leisurely about. He tried fiddling to get it right, but I guess that was my first view of a faulty pal 7.8kHz circuit.
I decided to get a locally imported NordMende 22" after seeing those swans.
When I started trying to learn about CTV, I bought a non-working 2000, and later a G6. In order to find my way around, I decided to remove all 405 line bits, to give a more reliable single standard set in each case. I sold them off cheaply, and slowly got more professional untill it became my living for a few years.
The very first set I was asked to repair, other than those I was selling, was one of those early Korting sets. They were also imported locally (the Korting guy had previously worked for the NordMende guy, so a similar sort of genesis, but he made a better fist of Korting imports). Well, that Korting hissed at switch on, with a small shaking picture. I had a new Marconi 50Kv EHT probe so checked out the value, and at 35Kv, decided to leave it alone, and advise scrapping it. In hindsight it was probably the (ECC83?) valve driving the EHT circuit's PL509, but then I just knew enough to know it was beter to walk away rather than risk too much X-ray doseage to me or customer.
Les.
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Old 6th Oct 2014, 3:49 pm   #30
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Default Re: Thorn 2000

The 2000 also featured a Tint control, not actually needed with PAL but in the early days I suppose people had heard of the problems with NTSC (never twice the same colour)
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Old 6th Oct 2014, 8:42 pm   #31
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Default Re: Thorn 2000

Hi
Early production G6s used a tint control too but unlike the American version it simply altered the biasing of the PCF200 output stages. As the 2000 used RGB drive it worked a different way but had the similar effect of mildly varying the hue unlike the dramatic NTSC adjustment!
I would imagine the Thorn valved colour (the 1000??) would have had a few tricks up its sleeve. I hope someone has details on it - I would imagine Thorn's designers would simply have thrown the Mullard book away and gone their own way with the design.
Glyn
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Old 8th Oct 2014, 11:42 am   #32
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Default Re: Thorn 2000

Re Post no. 30

Yes Bill, I remember the Tint control... It could" improve" some of the NASA space launch pictures ! (even though we were watching a PAL conversion of an NTSC original).

The biggest thing I can remember of the 2000 was keep having to reset the convergence. You would get it to an acceptable state, slide the convergence panel back and when you next turned on the TV, bingo!! - back to Test Card F looking like some of these recent 3-D TV images.

The Achilles heel for the 2000 I reckon was system switch arcing on 405-625 change over.
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Old 8th Oct 2014, 12:02 pm   #33
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Default Re: Thorn 2000

Convergence was a problem - I remember it well. The 405/625 switches used to change over every time you pushed a channel button. The cure was to cut a wire to the solenoids.
Don't forget the loose paddle on the tuner which needed re-soldering at regular intervals.
Mine was a Marconi version but it did give a good service for many years. Gave it to my parents when I bought a Sharp Linytron with thyristor timebase.
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Old 9th Oct 2014, 3:33 am   #34
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Default Re: Thorn 2000

...And no pincushion correction!
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Old 9th Oct 2014, 9:12 am   #35
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Default Re: Thorn 2000

But there was provision on the convergence board for the parts. I recall in Television magazine someone fitted some parts and got it working.
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Old 10th Oct 2014, 10:43 pm   #36
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Default Re: Thorn 2000

Yes, as always with Thorn, a few bob skimped resulted in a drastic reduction in picture quality. Certainly the bendy verticals because of no pincushion transducer, but also the dreadful mean level AGC with contrast all over the place depending on picture content. The chroma was also pretty noisy, though that applied to most of the first generation sets.
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Old 21st Oct 2014, 10:28 pm   #37
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Default Re: Thorn 2000

Quote:
Originally Posted by Focus Diode View Post
The BRC all valve colour set got a mention in the October 1966 issue of "Practical Television" when it was displayed with sets from other manufacturers at an exhibition. No photo of it unfortunately. Have any survived I wonder?
I suspect that may have been the same "modified American NTSC receiver" demonstrated by Ferguson a few months earlier and that BRC had been secretly working on its own all-transistor design all along.

BRC was also rumoured at the time to have been working on a beam-indexing single-gun colour tube but that may have been a bluff to foil their competitors.
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Old 22nd Oct 2014, 9:38 am   #38
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Default Re: Thorn 2000

I attended a session given by Thorn on the development of the 2000 and all the various tube types that had been developed. Most tubes are of American design and most patents were snapped up by RCA. The Beam Index tube was mentioned but all attempts to get it working reliably had failed due to the fast switching times required - well fast back in the 60's.
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