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Ultra 6658 Thorn 1400

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Jayceebee
(@jayceebee)
Noble V-Ratter Registered

This set has been waiting patiently for me to get round to getting it on the bench and doing something with it. It's a 20" Ultra 6658 fitted with the Thorn 1400 series chassis schedule D from around 1969, it seems to have a bit of an identity crisis as the rear cover says model 6656 which is a model I've been looking for some time. Anyway today I cleared my makeshift temporary bench and gave it a look over.

rsz 20190326 161054
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rsz 120190326 204825

The cabinet is in really good condition being a sort of melamine that Thorn used and was very hard wearing, not the wood printed plastic used on later models. The chassis is also very clean having had what appears to be just a couple of previous repairs. The tripler is the later ITT sealed type, the height control and a couple of resistors have been replaced but fitted rather untidily to the print side of the PCB. Rather worryingly some resoldering has been carried out to the system switching solenoid also.
Now normally I don't follow standard practice on the forums and reform electrolytics but give them full HT and see what happens. In the case of the 1400 the main can houses five electrolytics in one and as the set is in such good condition I have shied away from doing this and have ordered some components to make up a very basic reformer. As the capacitor is PCB mounted if it were to let go there's a good possibility of board being damaged.

rsz 120190326 160325

I still decided to give it some mains so I could asses the condition of the system switching, this was done with the mains filter cap C101 and HT rectifier W11 removed and am please to report heaters and a functioning system switch. I decided also to replace the five black Callins only to placate those that feel they should be removed on sight and as I had nothing better to do. Testing on my ESR meter showed that only one was actually faulty but that's not to say the others may have gone pop after a few hours of normal running. There are several of those infamous blue and white duomoulds but lets see if they are actually faulty in use.

rsz 20190326 191931

More follows.

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Topic starter Posted : 26/03/2019 10:18 pm
Nuvistor, The_Teleman, Red_to_Black and 2 people liked
colourmaster
(@colourmaster)
Reputable V-Ratter Registered

Hi john

Your set looks in excellent condition  I remember my grans neighbour having the same model  My Gran had the 24" HMV model. They were both rented from our local Rumbellows.

Regards

Gary.

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Posted : 26/03/2019 10:27 pm
Jayceebee liked
PYE625
(@pye625)
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A very attractive set indeed. ?

I have used a 15w lamp in series with the mains and remove a valve to break the heater chain when reforming electrolytics in more modern sets with a solid state HT rectifier. Obviously a proper capacitor reformer is better though.

Callins can be good, they can be bad. The bad 'un's will soon let you know though !  ?

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Posted : 26/03/2019 11:04 pm
Jayceebee liked
Jayceebee
(@jayceebee)
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Thanks for the comments, it's such a nice looking example that I'm not taking any risks with it. Email today says the necessary bits for the restorer are already on their way.

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Topic starter Posted : 26/03/2019 11:58 pm
The_Teleman
(@the_teleman)
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Hi John,

nice looking set can’t wait to see it working

chris

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Posted : 27/03/2019 12:13 am
Nuvistor
(@nuvistor)
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When was the 1400 chassis introduced?

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Posted : 27/03/2019 8:30 am
crustytv
(@crustytv)
Vrat Founder Admin

I'm 99% certain Thorn introduced the 1400 in 1967

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Posted : 27/03/2019 8:49 am
Nuvistor
(@nuvistor)
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That’s interesting, with all the work with the 2000 CTV chassis, they didn’t make use of that knowledge to at least put transistors in the signal stages like other makers did.

Pye for their sins with the integrated Tuner/IF strip is not a good example but the RBM TV135U set was, both introduced around late 1965.

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Posted : 27/03/2019 9:51 am
Jayceebee
(@jayceebee)
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My thoughts are that R & D resources must have been hard at work in getting the 2000 ready for market as they both were being developed along side each other. When you look at it the 1400 was largely in my opinion a rehash of the 950. The PFL200 went and the much more reliable 6F28 took its place as video output, another very reliable valve, the 30PL1 took over from the PCL86 in the audio department. Some clever tweaks made it a very cool running chassis for a valved set.

The following 1500 kept the same line stage apart in the use of a transistor as a DC amp, the frame stage was redesigned to do away with the biasing from the heaters but the FOPT was the same component. It's most radical design change was the IF department, again here R & D were perhaps more heavily focused on the 3000 series.

Yes, the RBM TV135U was an excellent set leading on to the superb A640 but as we all know the CTV25 wasn't, maybe their R & D should have concentrated more effort here?

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Topic starter Posted : 27/03/2019 4:01 pm
Nuvistor
(@nuvistor)
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The CTV25 was definitely not RBM’s finest moment picture wise, we didn’t sell many because of that point but the ones we did didn’t give too much trouble.

Not that we moved many dual standard sets.

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Posted : 27/03/2019 4:23 pm
glenz75
(@glenz75)
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A nice looking set, appears to be straight forward and easy to service and in good condition too which is a bonus. Hopefully bringing it back to life will give some pleasing results.

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Posted : 04/04/2019 9:10 am
Boingy
(@boingy)
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Hi JC,

I had a smoothing block blow on a 1500 once. It was in about the same position as the one you have. The aluminium cap took the neck off the tube on the way to being embedded in the workshop wall!

You are wise indeed, to reform that block 🙂

I like it that BRC put transfers on the component side of the PCB to show where the tracks went.

Good luck with the set 🙂

All the best,

Tony

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Posted : 05/04/2019 3:32 am
Jayceebee
(@jayceebee)
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After problems with a supplier I have now crudely constructed a working reformer, if anyone needs 50 zero Ω links let me know ? . Giving each of the four sections an hour has resulted in all being less than 100uA leakage which seems to be pretty good to me, having never done this before what is considered as an acceptable maximum?

Unfortunatly after doing some cold checks I have discovered R144 a 462Ω section is o/c, the hunt is now on for something as temporary fix to see if first light can be obtained today.

Posted by: Boingy

Hi JC,

I had a smoothing block blow on a 1500 once. It was in about the same position as the one you have. The aluminium cap took the neck off the tube on the way to being embedded in the workshop wall!

Hi Tony, I've only ever seen one smoothing can let go and that was firmly strapped to the chassis, I think it was a Murphy V500 or something similar back in the day just about at the end their service life and what a mess it made. I wasn't taking any risks with this one.

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Topic starter Posted : 06/04/2019 4:19 pm
Jayceebee
(@jayceebee)
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Couldn't wait, switched on with the o/c section and look what we have ? . Really bright raster but frame is running a bit slow and because the o/c section feeds the brightness pot there's no control but I'm shocked, I really expected the Mazda CRT to have to be coaxed into decent emission. One happy bunny here.

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Topic starter Posted : 06/04/2019 4:52 pm
glenz75 liked
Jayceebee
(@jayceebee)
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So chuffed I forgot to add the pic.

first light
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Topic starter Posted : 06/04/2019 5:23 pm
glenz75 liked
crustytv
(@crustytv)
Vrat Founder Admin

Raster-licious, well done that man ?

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Posted : 06/04/2019 5:39 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Managed to make up a 450Ω Xmas tree, even robbing parts from my newly constructed capacitor reformer to see what other problems were there. The capacitors in the grid bias feed for the PCL805 from the heater chain have obvious problems which was entirely expected, no UHF reception although the plastic cams are intact. There is also a spot burn on the centre of the CRT phosphor which is a shame given it has pretty decent emission, not a bad start though.

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Topic starter Posted : 06/04/2019 8:26 pm
PYE625, Nuvistor, Red_to_Black and 1 people liked
glenz75
(@glenz75)
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That is looking really promising despite the spot burn, you should have a very nice set when its all fixed ?

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Posted : 08/04/2019 1:45 am
Jayceebee
(@jayceebee)
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Hi Glen, so far this set hasn't given me much trouble although I may live to regret saying that. Everything appears to be stock faults, loss of UHF being due to hard grease together with poor earthing of the rotor. Careful removal of the nickel plated earthing springs, cleaning and retensioning them has cured that.

tuner1

One odd thing going on though which I've not come across on a 1400 is quite a bit of brightness drift, I have the Aurora output on CH8 and setting the brightness to normal all is fine until CH9 is selected which is on the way to UHF on the turret. As soon as CH9 is hit the Aurora test card appears way off tune of course with heavy sound on vision but the brightness immediately drops to almost nothing before returning to normal over a period of about a minute when on UHF. Not sure if it's an AGC issue or something in the video output stage as yet, the AGC diodes caught my eye as the look like a smaller version of the awful M3 types.

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Topic starter Posted : 09/04/2019 10:37 pm
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glenz75
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I really cringe when I have to delve into tuner mechanisms or tuner related faults, they can be so timing consuming and fiddly! At least you've sorted out the UHF side of things now. If those AGC diodes are a known problematic component, then I'd be swapping those out first and see if the fault clears up, if not you may have to delve a little deeper... ?

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Posted : 10/04/2019 2:02 am
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