I've long wondered about the significance of the coloured spots (Green, Yellow & White) as found on the Thorn diode split transformers. I'm aware this is something Thorn started way back on their older lopts.
I have a number of these new in stock, for example TX100 90-degree FST have yellow spot stated on the box but nothing on the lopt. TX100 110-degree FST no spot but box states green spot. TX90 90-degree no spot but box states white spot. Many boxed from the likes of CPC also do not have any indication, just a code etc. Then I have pulls that do have actual spots.
What were the spots indicating, why were they used, as often they've fallen off leaving only the imprint of the circle where the sticker once was. Why not just rely on the printed code, and finally were there other colours?
This info would be great to capture as I've searched and cannot find anything. I thought it would be nice to document it, similarly as I did for the Jelly pots and EHT trays.
p.s.
I've also got a few pulls, a couple of which I tested this afternoon. The green spot one, I believe, was an HR7125 had a shorted primary, showing error 4 on the tester. The smaller one, I believe to be a TX90 HR7151 was OK showing the correct 16.5kV. The spot on that is neither white nor yellow, more beige. I can't figure if it's faded yellow or white.
I've taken to labelling them up myself with more relevant info, but the whole spot thing is fraught with ambiguity, well for me, it is a minefield!
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@crustytv As far as I understood it the spot identified the LOPT with regard as to what CRT was fitted. A TX100 chassis for a 22" 30AX CRT would have a different colour spot to a TX100 chassis for a FST PIL CRT. The scancoils, raster correction etc would be different. But the basic printed board would be the same with just component values being adjusted to suit. In practice some chassis were not too fussy. On a couple of occasions I tried a different colour spot LOPT in older sets when I had a second hand LOPT of the wrong colour spot. I can't remember what did interchange but I wouldn't be surprised if a LOPT intended for a FST set would work in a non FST set. When the sets were old we had a few dodges to keep a set going that would have been otherwise beyond repair...
From what I can remember for the TX100 & TX90 with TTR part numbers.
TX100
20" 90° Blue spot TR4179
21" FST 90° yellow spot TR4181
22 & 26" 110° Green spot TR4180
24 & 26" FST 110° No spot TR4183
TX90
20" TR4184 White spot
14" Pink spot? Don't remember this one as the failure rate was very low.
Hope it helps.
John.
My information says they were 5 different spots.
Little bit more info on your spots Chris.
Found this too if you don't allready have it.
Thorn LOPTX spots.
There expensive, what supplier was that, one of mine was wizard distributors and I thought they were expensive.Thorn LOPTX spots.
Those prices were from Willow Vale and were for the orignal manufactures parts. They also sold the equivalent parts from HR and Konig equivalents at prices that could be quite a lot cheaper.
Thanks to all for the data input, even with all that I'm not sure fully I'm clear on all of it, there seems to be even more colours than I first thought.
Michael's books are very interesting, having the long part numbers and in some cases even tie up to actual models, this is superb! I'm now actively looking for one of those Wizard books online as it looks worthy of a scan, so much valuable data in there for us TV folk.
I'll keep an eye out for willow vale catalogues too. Furthermore, I have all the HR-Diemen data in the form of CD-ROM, and all their LOPT schematics, but It's so unfriendly to get at, as is their website, but at least you can tie a model to an HR code but not to a manufacturer code. I cannot find anything for Konig.
As I've mentioned, the dilemma is correlating Konig, CPC, HR-Dieman and original manufactures codes to correctly identify a LOPT to a specific model and when the spot is missing....!
I fear I've stumbled into a minefield...... Yikes!
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