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Old 27th Jun 2021, 8:53 pm   #1
Niechcial,Steve
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Default Ferguson Transvista 743T

I've always wanted to get my hands on one of the very first generation of British transistor tvs and so was delighted when this one came up on that notorious auction site a few weeks back. It's a very clean and almost complete example including the ingenious pop out sun shield. It came with 12v battery lead, but no mains lead, and one of the rod aerials is missing. The battery lead struck terror on first sight because it is fitted with a two pin mains plug. My fear was that someone might have tried to connect it to the mains via this, however all was well internally with no fuses blown nor any other sign of mis-applied mains. My guess is that the set was probably used long term on external 12 v in a caravan or similar. The battery pack was also present. Fortunately there is no sign of corrosion damage from its vapours, other than possibly the LOPT as discussed below. The battery fell apart on removal, and a picture of it is attached. The whole thing weighs a ton- 24 lbs to be precise according to Graham Gosling's excellent article in the Spring 2021 BVWS Bulletin.

After checking for shorts, I plunged straight in, connected a channel 1 signal and 12.5 volts external power and switched on. I was rewarded immediately with some sound (albeit a little distorted) but no raster. with tube heater glowing. Hooking up an EHT meter showed all well there , but the -40V line was virtually nil, and 200V line was low. Both of these are derived from the LOPT. The OA81 rectifying the -40V line was o/c but replacing it made no difference. It turned out that the single strand enamelled copper lead- out wire from the -40v LOPT winding was broken about a cm from the connection tag. This meant a very tricky job of scraping the enamel off the wire and soldering another strand of wire to connect it back to the tag. It was a very delicate case of balance between using enough force to scrape the enamel versus not tearing the wire away altogether- all in a very confined working space, Fortunately I succeeded and the 40V line was restored. I don't know why the lead out wire failed at the point it did. There was no visible sign of green spot or corrosion anywhere, but with the battery directly underneath, I guess that green spot is the best explanation.

Replacing the 0.25 mfd decoupler on the 200V line also brought that up, but still no raster. At this point I noticed that plugging/unplugging the aerial caused the EHT to rise/dip slightly, likewise operating the brilliance control caused the EHT to rise/fall, so obviously the tube was conducting. The answer to the no raster was the ion trap. This is of an unusual design being a rubber ring with a magnetised metal ring around it. The rubber had shrunk allowing the whole assembly to slide backwards down the tube neck. Once again Graham's article was very helpful with a photo showing the correct position of the ion trap. Manipulating it back brought up a raster with a very faint unlocked picture in the background. And that is as far as I've got. I think I will now go in a slightly different direction and get rid of all those Hunts caps before going looking for the low gain problem.

As Graham says, the original service manuals for these sets are rarer even than the sets themselves .The RTV Servicing article gives all the basic stuff, but unfortunately not the oscillograms which it would be very good to have.
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Old 27th Jun 2021, 8:58 pm   #2
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Default Re: Ferguson Transvista 743T

sorry- forgot attachment
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Old 27th Jun 2021, 9:08 pm   #3
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Default Re: Ferguson Transvista 743T

Hi Steven,
I learnt recently the CRT is a camera viewfinder tube. It's an excellent receiver and shows just what the Thorn design team could create.
Servicing data for the 743T can be found in the 1961/62 Radio and Television book. Not absolutely sure but I believe the set was announced to the trade in late 1960.
Those AF114 transistors are known to fail. My Ever-Ready experimental transistor TV employs a similar IF board.

DFWB.
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Old 27th Jun 2021, 9:13 pm   #4
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Default Re: Ferguson Transvista 743T

Thanks David I'm looking forward to working on it. Sounds like the tube was probably built to professional monitor standards so hopefully might be half decent.
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Old 5th Jul 2021, 9:13 pm   #5
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Default Re: Ferguson Transvista 743T

Good progress on this. I changed all the Hunts on the IF panel and checked the AF114s in the vision IF. They were all fine- no hint of tin whisker shorts (unlike the 3 NOS ones I bought as standbys, all of which had shorts to case). Not having found a fault, I switched on again without much optimism, but the low gain fault had disappeared leaving me with a good contrast but unlocked picture. In the process of removing and re-inserting the AF114s I guess I may have made good a dry joint. Both line and frame are out of range of the hold controls, but I managed to lock a double image on the line showing promising signs of a good tube. I'm now half way through re-capping the timebase board.
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Old 5th Jul 2021, 10:27 pm   #6
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Default Re: Ferguson Transvista 743T

The fact both the Ferguson 743T "Transvista" and the Pye TT1 were announced to the trade in 1960 shows that television manufacturers in the UK weren't that far behind the USA and Japan.
I believe in 1959 the Philco "Safari" was the first all transistor TV set to be offered for sale to the general public.

DFWB.
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Old 7th Jul 2021, 7:38 pm   #7
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Default Re: Ferguson Transvista 743T

Yes the Safari was produced in 1959 and is an excellent little set- I have had one for several years and it is very reliable (shouldn't have said that).
I guess the Transvista and Pye TT1 were both outsold by the Perdio because it offered a good screen size to price compromise. Can you imagine lugging the weight of that TT1 off to your caravan or boat? The 12volt set market can't have been that big, and in 1960 a lot of customers seem to have already opted for the valve ECKO TBM of a few years earlier judging by the large numbers of them still about. It is amazing though that Thorn did not produce another all transistor portable for nearly 20 years.

Having re-capped all the paper caps. both line and frame locked nicely in the middle but I was left with low height and top stretch. Luckily this turned out to be the second electrolytic I tried- C122 which is- feed back/bias on the base of the driver transistor. I now had a very good, bright, linear picture but the focus control was not upping the voltage quite enough to bring the focus in as far as it should go. Checking the 220v line which feeds the focus pot, it was about 25% down, as was the 40V line and the EHT. Mine is an early Schedule A model which has a 7R resistor instead of an inductor feeding the HT to the line output transistor. (By the way, the line output transistor fitted is neither the earlier 2N458 nor the later N7D). Anyway, halving the value of the feed resistor has brought everything up and the focus is now very sharp.

This just leaves me with the distorted sound to remedy. I will then probably re- build the battery back using NiMh cells and a built in constant-current charge regulator.

Does anyone know what heater voltage the CRT is actually designed for? I can find no info on the crt. There is no voltage regulator on this set, and according to Newnes the voltage across the heater can vary between 10.9v and 12.3v depending on whether mains or battery power is used
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Old 7th Jul 2021, 9:17 pm   #8
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Default Re: Ferguson Transvista 743T

An AW17-20 CRT was made by Valvo and was designed as a viewfinder CRT.
https://www.radiomuseum.org/tubes/tube_aw17-20.html
This tube has the standard 6.3volt 0.3amp heater. Neck diameter is 38mm. B12A base.
The AW17-20 was used in the EMI type 203 camera.
Perhaps the AW17-10 with it's special 11.5 or 12volt heater was made by Mullard at the behest of Ferguson Ltd.

DFWB.
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Old 10th Jul 2021, 10:22 pm   #9
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Default Re: Ferguson Transvista 743T

Thanks David.
I've just been re-reading your post on the Ever Ready experimental transistor TV. That was a truly remarkable set with a power consumption near the 3w mark. The Ferguson draws twice that- 6.72W.
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Old 11th Jul 2021, 10:10 am   #10
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Default Re: Ferguson Transvista 743T

Ferguson were great supporters of Mullard valves and tubes and must have taken a large percentage of Mullard production.
Mullard produced the TY86F [F for Ferguson] EHT rectifier with a 7.5V heater to employ as a replacement to the EY86 that was suffering a high failure rate due to a design flaw in the LOPT. This produced a higher heater voltage than the 6.3V EY86 could cope with.

I don't think it would have been a problem for Mullard to produce a special version of the AW17-20 CRT for such a good customer. J.
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Old 13th Jul 2021, 7:14 am   #11
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Default Re: Ferguson Transvista 743T

I'm sure that's right John. Presumably Ferguson went over to Mazda valves and CRTs when they became part of thorn?

The sound fault on this set has led me a merry chase. The voltages in the O/P stage were well out. Replacing the O/P transistors corrected that and increased the volume a little, but the distortion was still bad. I tacked in new detector and limiter diodes which cured it for a few minutes, but then it reverted to distortion. Checking both sides of the noise limiter diode with a crystal earpiece confirmed that's where clipping was taking place. To cut a long story short, I believe the fault was the 8mfd cap which couples the the detector to the limiter. Time will tell!
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Old 13th Jul 2021, 8:51 am   #12
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Default Re: Ferguson Transvista 743T

Take a look at Onjoj on YouTube tackling a
TV62, video is in 4 parts.
https://youtu.be/fw_Vnol7AwE
The set had a slightly partially shorted heater which cleared itself.
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Old 14th Jul 2021, 11:00 pm   #13
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Default Re: Ferguson Transvista 743T

Attached is a picture of the set running. I have ordered some sub-C NiMh cells to make up a new internal 12v battery
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