Baird T18

[Heatercathodeshort]

Try the set with the frame output valve removed. This should produce a frame collapse even with very low emission tubes. You may have to turn the room lights off to see the faintest of a trace. This will give some idea if the tube is faulty. John.

[sexton_mallard]

Originally Posted by Panrock

Yes, your pictures of the tube internals at different times have been taken from different viewing positions, but there does seem some serious misalignment between (what I take to be) the electron gun and the modulating electrode. It's as if the internal mountings are loose and any movement or tilting of the tube could run the risk of changing the electrode positions. Also, the 'tapping' should have been the last, not the first, thing to try, as I mentioned.

What do others think?

Steve

It does appear as if the electrode structure has been deformed possibly by a hard knock perhaps which somehow did not shatter the glass envelope of the CRT.

[Freya]

The gun is completely mis aligned, there is no chance of the electron beam will reach the face.

[high_vacuum_house]

Good evening,
It looks to have had a very heavy sideways knock in the past. How that tube didn’t implode is beyond me!

The first picture on post #16 shows quite clearly a large eccentricity exists between glass tubing and the final anode I believe, just before it enters the section where the scan coils are located. It would be impossible to get the beam of electrons down there in any satisfactory way to get a nice focussed spot in the middle of the screen. I am afraid it is going to need another tube.

I would not volunteer to give that tube a very hard knock in the other direction in a vain attempt to realign those electrodes!! It would be easy to bend them back if there wasn’t a high vacuum being held back by an enclosed glass envelope.

Christopher Capener

[Heatercathodeshort]

It certainly is out of line. As a last experiment fit an ion trap around the neck approximately in line with the gun and turn it at the same time twisting it in an attempt to bend the beam partly back on line. The adjustment may be critical. John.

[Ed_Dinning]

Looking at the amount of offset in the gun you may well need a modern Niobium magnet to achieve that much shift

Ed

[Panrock]

What metal will the electrodes be made of? Just wondering if a magnet could be used to physically shift them back into line...

Steve

[Michelb]

Hi all,
thanks for your replies.

I tried to restore the alignment using a powerfull magnet, but I didn't succeeded to move the cannon gun to the opposite side.

I also tried to use a ion trap, I was very confident it could work but I didn't succeeded to get a result with that. To be more precise I used two different ion trap. In the next days I will continue with some new attempts.

Then finally I start to think about replacing the CRT, which is not an easy solution because the replacement model are not common.
Like you I don't understand how this part has moved inside the CRT, it is not very logical, it's hard to believe it was not made this way, but it should have been aligned to work.

[high_vacuum_house]

Good morning,
I don’t think the CRT was made that way as there should be no eccentricity between those parts. My guess is that the set has fallen off a table sideways at some point and the impact on the CRT was just short of snapping the neck off the tube.

As an experiment to prove that the rest of the television is working, it might be possible to substitute a CRT and scan coil assembly from an old solid state monochrome receiver. The results may be poor due to compatibility but should be good enough to see if your receiver is working.

Christopher Capener

[FERNSEH]

The Mullard MW31-18 CRT has been used as a replacement for the Cathovisor 12MW2A. 6.3V heater, tetrode gun assembly.
Brimar in the UK marketed the CinTel 12MW3 as the C12D. 2V heater, triode gun assy. Max EHT 7KV.
I have the full service manual for the Baird T18 and T20 TV receivers.

DFWB.

[Michelb]

Hello,

I have some news, I did anothers attempts and finally I got something.
The first tries done to redirect the electron beam with a ion trap were not in an absolute darkness, I was with lights turned off and drawn curtains.
One evening very late I did a new try and finally adjusting the ion trap I was surprised to see some inclined lines on screen!

I was able to see a bad shaped and jumpy display (but with vertical and horitonzal deflection). The display was not good because the top right part of the screen remained black like if the beam couldn't reach this part (whatever the ion trap position), I was not able to really stabilize the jumpy display and to get the picture of something despite my attempt to enter a video signal.

Entering a composite video signal (converted to 405 or 441 lines with the Hedgehog) directly on G1 of final TSE4 tube : I didn't saw a picture, only inclined line, jumpy display, very poor brightness : the contrast and also the brighness potentiometers were uneffective. It is normal for the contrast but weird for the brightness control.

Entering through the aerial : it seemed there was a picture displayed but the display was amazingly blurry (impossible to recognize anything), more stable, not jumpy, and the contrast and brightness controls were both working.
However anyway very poor brightness : I tried to make some photographs but it was impossible to catch, photo are black.

Moreover I suspect the tube to be very gaseous, while running, the back of the CRT (I mean between the cathode and the concentration coil) is clear blue lightened, and touching the on-screen display reacts like if something smooth moves away around my finger.

I also noticed I have a round ionic mark in the middle of the screen.

I speak with a past tense because for now I have a main issue caused by a mistake I've done : I touched at all the tubes when the TV was running to check the reaction and if a there may be a bad contact somewhere which could improve something.
And touching at one of the two MP41 tube it did some sparks (also in the UR1C) then nothing, the TV turned off. The fuse was blown, I replaced it, but since that I no longer have any deflection, only a huge spot at the middle of the screen. All the timebase part is not working anymore.
I noticed after that the MP41 tubes have moving parts inside, it seems to be normal, the attachment of the electrode are not rigid, and I guess that touching the tube while working I created a short inside the tube and damaged something else.
I tried to inverse both MP41 tube, and also both 2D4A tubes but it changed nothing. I have in fact since this mistake a huge loss of main HT, when all is plugged (Vision and Time base chassis) it finally drops to 50v only (before I had 337v). I didn't find a shorted component anywhere, and I don't think I have one because in this case it should smoke somewhere. I simply think my IW4/350 main rectifier tube is dead. I just ordered a new one and wait to receive it.

A part this issue I am thinking at what to do next, the CRT mentioned in the post above would be sure a good replacement solution. But I don't have a clue to find a C12D or MW31-18. A TV collector friend lent me a tube he has to do some testing : a 10" Sylvania in good health, it is an US flat round tube. It is not a good replacement tube for the Cathovisor type 12 but it could be great for further test when my main HT issue will be solved. It is not a tetrode, I will have to feed the G2.

[Michelb]

Hello,

I made few small steps forward since the last time.
First I repaired the mistake I've done, I found out I had 2 dead tubes : IW4/350 and UR1C... So I replaced them.
When the tv was able to be turned on again I did some more tests with the Cathovisor picture tube, each time in an absolute darkness to try to view something.
But I realized this CRT is definitively worn out with a very low power of emission. It was not easy to catch it on a foto, I attached one (see foto 1).

I tried to install the 10" sylvania picture tube a friend collector lent me but it was not possible as the back part was too large to pass through the concentration coil.
At end I picked-up a MW31-15 picture tube, thanks to this friend (he sold it to me), and it is in very good condition (it was measured at 650ma).
(see foto 2)

I winded a 6.3v transformer for the heaters, I also added in my circuitry an adjustable power line (from 0v to 250v) to feed the G2 (or "A1" in the technical doc) and met the voltage expectation, then I modified the brightness circuitry to be able to adjust it to a larger voltage range (from 0 to 70v).
I kept the video signal unchanged connected to G1 with a near 0v voltage.
For the EHT I am still waiting at the moment to receive a new transformer to be able to get around 8kv. Anyway I did some tests as is with my 5kv EHT.

First test I turned it on and quickly the picture tube worked very good with a nice brightness, but nothing on screen happened when I entered a video signal through the aerial connector (a round 2 pins female connector). When I disconnect the aerial cable from the back on the hedgehog converter nothing happens, there is no reaction on the display, maybe one of the TSE4 tube is dead in the vision part.
(see foto 3)

Then I tried to enter a video signal on the G1 of the video amp tube (the final TSE4 tube).
I got at best some vertical bars, and a picture almost invisible in the back (see foto4)
I realized it was the result of few images not synchronized, but adjusting the sync line potentiometer is not an easy task. When I am going too far with this potentiometer the electronic doesn't like it : it whistles, it screams, I got smoke (I didn't understand from where),... It was almost impossible to push the setting as far as it takes.
So I tried some others setting with the Hedgehog converter and finally I succeed to synchronize a "picture" at 525 lines! In this case the electronic doesn't suffer at all as the picture appears at the beginning of the potentiometer range. But it is not a good picture, too clear, no contrast, it's hard to see something (see foto 5 with a dvd main screen).

I ask myself if it is a good thing to plug the video wire (modulator) on the G1 of the MW31-15.

[German Dalek]

Hi,
I am just short in time - again.
Some sets are kathode-driven and some sets are grid-driven.
It depends often on the TV standard!
I hope this is a correct translation and you know what I mean.
According to this, you have to check the surrounding voltages of the CRT,
when you are going to connect signals directly!

Good luck!
German Dalek

[Michelb]

Hello,

Interesting progress today, I upgraded the EHT transformer to an higher one. I now have as I expected 7.8kv which fits well the MW31 CRT specs.
Unfortunately the HVR2 EHT rectifier tube didn't like the new voltage, it was detonating with huge sparks on the anode, so I had to install an EY51 (but i keep the HVR2 tube heated for the visual).

I tested my TSE4 tubes (from the vision part) on a tube tester and the 3 are good. So i did some new attempts to enter through the aerial plug, and at last it worked!
However I still can't synchronize a 405 lines picture because I can't reach it, it is too far on the potentiometer range and as described the last time the circuitry is dying when I push too far... But I succeeded to catch a 441 lines picture. I didn't investigate this topic yet, I guess I would need to change a capacitor and/or resistor on the timebase part to be able to catch 405 lines.

The focus can be improved, I will move my focus coil a little more in the front direction to see what happens.

[Panrock]

Well done!

I'd keep it working at 441-lines... this might be an interesting historical detail. I wonder if there is a service area map for the wartime 441-line transmissions from the Eiffel Tower? I believe a special aerial was installed on the south coast of England to receive these.

Steve

[jhalphen]

Hi to all,
Hi Panrock,

some info about the Paris 441 line Tx on Wikipedia. RF power is quoted as 30KW and coverage area as 62 miles/100km. Frequencies are nearly the same as London Alexandra Palace (42 Vision & 46 MHz Sound).

https://en.wikipedia.org/wiki/441-line_television_system

Info about the 1943 FernsehSender Paris TV station during WWII. Unfortunately wiki is only in french :
https://fr.wikipedia.org/wiki/Fernsehsender_Paris

photos of occupied Paris TV, 1943 :
https://achdr.over-blog.com/2021/01/un-heritage-meconnu-de-l...notre-television-en-441-lignes.html

and here; below, a photo of the Eiffer tower's antennas in 1949. The 441 line aerials are still in operation until 1956 when a fire destroyed the transmitter. It was never repaired as 819 was now the new standard.
https://forum.telesatellite.com/showthread.php/1679-Bien-ava...n-France-dans-les-ann%C3%A9es-50-60

Best Regards
jhalphen
Paris/France

[stevehertz]

Out of interest here's a photo of a Bush T18 that I owned up until about 1991. It went to a gentleman who back then spent a lot of time at Gerry Wells place.

[stevehertz]

There's this video about the restoration of T18 that may be of use, but if not almost certainly of interest.

https://www.youtube.com/watch?v=cnRg_06BLgA

[Michelb]

Hello,

For now I don't touch at the sync line circuitry, I will add sound these next days. I already installed the last sound tube (PENB4) but I think I will also need the previous one : SP4B to control the volume.

I don't know if it was modified to change the range of the sync line, I will do some measurement to check this. Who knows the story of this TV, why it was in france, since how many time, why the bottom chassis was missing, how the canon was so much misaligned. Lot of mysteries.

Originally Posted by stevehertz

Out of interest here's a photo of a Bush T18 that I owned up until about 1991. It went to a gentleman who back then spent a lot of time at Gerry Wells place.

Interesting, maybe it is still existing somewhere ? Was it working?

Originally Posted by stevehertz

There's this video about the restoration of T18 that may be of use, but if not almost certainly of interest.

https://www.youtube.com/watch?v=cnRg_06BLgA

Oh yes I saw this video, it was interesting for me. It looks like to be the Baird T18 of TNC (Trevor). It is working quite well now.

By the way I discovered there is a Baird T18 in a museum in Norway :
https://digitaltmuseum.no/021028793967/fjernsyn

I add some pics, the quality is not at the best because I did screenshots from a video.

[Panrock]

Originally Posted by jhalphen

Hi to all,
Hi Panrock,

Best Regards
jhalphen
Paris/France

Jerome, thanks for the links!

Here's one about the British reception of the Eiffel Tower.
https://www.earlytelevision.org/raf.html

Now I know the power (30kW) and the zero tx antenna gain, I could prepare a service area map using RadioMobile (software).

Steve