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Old 19th Dec 2016, 7:33 pm   #41
FERNSEH
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Default Re: A scary Baird T23.

One fine day this restoration job will be completed. This set has always had a vertical picture shift problem. Today the centre point of the CRT mounting plate relative to the focus coil assembly was checked, there was a 4mm displacement
To correct this error a new focus coil adaptor board has been made, the three 2BA threaded rods used to support the focus coil have been moved forward by 4mm. The new adaptor board will painted with the usual blackboard paint.

DFWB.
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Old 20th Dec 2016, 5:21 pm   #42
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Default Re: A scary Baird T23.

The revised CRT supports are ready to accept the replacement tube. The whole assembly is much more rigid than it was before.

DFWB.
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Old 21st Dec 2016, 11:22 pm   #43
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Default Re: A scary Baird T23.

That was a scary job. The replacement CRT has now been installed. Once again the bulb shape is different, that's three versions of the Cossor 65K we've come across. On this occasion the CRT bulb mounting plate had to be raised by 1/2 inch compared the position of the preceding tube. Those cutouts in the original CRT board have proven worthwhile after all, there is a good clearance between those horns and the wooden board. The anode connector stem is slightly longer than that of the other tube.

But is the replacement tube any good?

DFWB.
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Old 22nd Dec 2016, 12:17 am   #44
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Default Re: A scary Baird T23.

Nice installation!
Don't keep us in suspense too long.

Peter
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Old 22nd Dec 2016, 11:57 pm   #45
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Default Re: A scary Baird T23.

After all that work the results are hopeless, in fact the replacement CRT is even worse than the one that was recently removed. There are two more Cossor 65K tubes upstairs, maybe one of those might be a bit better than the last two tried out in the set.

DFWB.
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Old 23rd Dec 2016, 5:41 pm   #46
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Default Re: A scary Baird T23.

That is disappointing to here but now you have modified the cabinet it will be a lot easier to fit the next CRT in.
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Old 23rd Dec 2016, 6:15 pm   #47
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Default Re: A scary Baird T23.

Hi Robin,
That's right, after doing those simple modifications to the CRT mounting arrangements removing and refitting the tube is a lot easier than it was, and less scary. Actually, I've noticed that the frame transformer's extended pole pieces are not centralised about the CRT neck and are offset to the left. So before another CRT is installed the position of the focus coil mounting board will be checked to confirm it's central position.

DFWB.
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Old 23rd Dec 2016, 10:26 pm   #48
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Default Re: A scary Baird T23.

Hi David a bit of a set back but you have 2 more tubes to try regards Bob
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Old 23rd Dec 2016, 10:34 pm   #49
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Default Re: A scary Baird T23.

Hi Bob,
It might even finish up with John's 65K/2 tube, but before that can be done a new adaptor plate will have to be made to suit the different bulb shape.
Let's try the two other 65K tubes first before such drastic measures become necessary.

DFWB.
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Old 24th Dec 2016, 2:09 pm   #50
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Default Re: A scary Baird T23.

Hi David worth trying the other two but John's tube will be no bother to you to fit as you are the expert with the ADAPTER PLATES regards Bob
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Old 24th Dec 2016, 9:17 pm   #51
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Default Re: A scary Baird T23.

Hi Bob,
I've brought down from upstairs another Cossor 65K, the getters are milky but there are no indications that the tube has ever been installed in a Baird T23. The only two other sets that were known to employ this tube were the Cossor 1210 and the post-war version model 900.

DFWB.
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Old 24th Dec 2016, 11:47 pm   #52
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Default Re: A scary Baird T23.

I Have a spare CRT, David. You are very welcome to it.
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Old 25th Dec 2016, 1:50 am   #53
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Default Re: A scary Baird T23.

Hi Brian,
many thanks for the offer, I think I'm going to need it. I'll try out the 65K retrieved from the cache of tubes kept upstairs but I'm not expecting much in the way of results.

DFWB.
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Old 8th Jan 2017, 12:03 pm   #54
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Default Re: A scary Baird T23.

Have you had enough of the baird for the time being david ?
Peter and I were looking forward to seeing pictures on it.

Robin
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Old 8th Jan 2017, 1:14 pm   #55
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Default Re: A scary Baird T23.

Hi Robin.

I've found another 65K tube from the upstairs storeroom and there is no indication this tube was ever fitted in a Baird T23, as there is no ring mark around the cloth covered CRT bowl.
So all it takes is for me to gather up all the courage and install the CRT.

The tube can easily be lifted out from the cabinet but the reinstallation is a bit tricky. Also, although the CRT focus coil was recently repositioned fore and aft in the cabinet it has been noticed there is a slight inclination of the CRT from left to right. It's likely the focus coil mounting board will have to be remade again.

DFWB.
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Old 9th Jan 2017, 1:02 am   #56
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Default Re: A scary Baird T23.

Quote:
Originally Posted by line sync View Post
Have you had enough of the baird for the time being david ?
Peter and I were looking forward to seeing pictures on it.
Yes, it's good to take a break from things when they don't respond as you'd like. I've certainly got my fingers crossed for the attic CRT and if it flops there's still hope on the horizon with the offers from John and Brian.

Peter
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Old 10th Jan 2017, 9:56 pm   #57
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Default Re: A scary Baird T23.

The CRT was taken out last night. Looking at the replacement I'm not sure if this one is any good either, the getters are milky.
The focus coil mounting board will remade so that the CRT can be centralised, the second attempt. I'll get it right this time?

DFWB.
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Old 11th Jan 2017, 12:00 am   #58
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Default Re: A scary Baird T23.

Fingers crossed David!

Cheers
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Old 11th Jan 2017, 2:15 am   #59
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Default Re: A scary Baird T23.

Hi Lee,
If this tube doesn't work it will have to be a trip down South to collect the tube Brian has offered me.
A picture of the internals of the T23. The shelf that carries the timebase and sound-vision receiver units can be slid out without having to remove the CRT. In the Baird T5 the focus coil support is situated at the same level as the shelf. In the T23 the wooden focus coil support is raised up by four inches because the Cossor 65K is much shorter than the Cathodevisor 15MW1. In the T23 it is still possible to slide out the shelf for service.

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Old 13th Jan 2017, 4:08 pm   #60
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Default Re: A scary Baird T23.

These early 15" tubes certainly had a vacuum problem. I don't think their makers realized the importance of large getters.

Central Tubes used to spot weld two large getters mounted on spring steel that was in turn spot welded to the end of the gun assembly. This allowed them to lay flat against the flare of the cone as the new gun was slid into the neck to prevent corner shadowing.

It was quite a feat to evacuate such a large glass structure and I suspect this was never carried out at a high enough temperature that would have expelled gas from the screen chemicals, glass and gun assembly, hence the very short life of early electrostatic television tubes.[Lots of air molecules in the huge and intricate gun]. John.
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