A scary Baird T23.

[FERNSEH]

News Flash! The CRT was fitted this evening, this is the third Cossor 65K tube to be tried out in this set.

DFWB.

[FERNSEH]

This proves that it was a good idea to make those cut-outs on the CRT mounting board. Even with the cutouts the final anode connector is precariously close to the edge of wooden board. It's the same for the evacuation "horn". Remember that these tubes were made to very wide manufacturing tolerances.

DFWB.

[unitaudio]

Might that be a problem when moving the television or is it very solid?

Regards, Paul

[FERNSEH]

Hi Paul,
The CRT seems to be fixed firm enough into it's mounts but I think that a different type of anode connector will be a good idea.

DFWB.

[Jac]

Hello David,

Let's all hope this CRT is much better.
Scary business - lugging these monsters around!

Looking forward to a perfect picture!

Jac

[Heatercathodeshort]

I've been sweeping out my atomic bomb shelter David. Reminds me of that great old film 'Wages of Fear'.

Those tubes are horrendous! I wonder how many went pop during assembly? Very difficult to evacuate such a monster. I thought the 15" 3/6A in my HMV 1803 was about as big as you could handle. John.

[FERNSEH]

Originally Posted by Jac

Hello David,

Let's all hope this CRT is much better.
Scary business - lugging these monsters around!

Looking forward to a perfect picture!

Jac

Good evening Jac,
There is a distinct chance that this might be third time lucky with this CRT. After reconnecting everything together I was greeted with the usual dim raster, not another duff CRT I thought. The brightness control had hardly any effect, likewise the contrast control. My attention was diverted to something else, an attempt to revive a Vestel LCD TV with an USB reprogramming stick, that job proved to be a waste of time. When I returned to the Baird T23 I was amazed to observe very bright illumination of the screen.
It's most likely there is a bad connection or short circuit on the CRT base socket, moving the base about secures the bright picture.
The sound output is very low and the line oscillator is running at the wrong frequency, before any fault finding commences it might be just possible the power connectors for the sound and timebase units are simply transposed.
So that's the good news, the bad news is that CRT will have to come out again. The new CRT focus unit mounting board fouls the refitting of the RF unit, it needs that corner to be sawn off, see attachment. Now I don't fancy doing that with that bomb like CRT in situ. While the CRT is out the base connections can be checked.
All being well I reckon this Baird TV could finish up having the brightest picture of all among my collection of pre-war TV sets.

DFWB.

[Jac]

Hello David,

This indeed looks very promising with lots of light!
Finally a very good tube.

Jac

[McMurdo]

getting exciting!

[FERNSEH]

It certainly does look promising. I'll be returning to the workshop later this evening. The first thing to do is swap those module connectors around and see what happens.

DFWB.

[FERNSEH]

Braved the cold and the rain and trudged back to the shop to do more work on the Baird. Here's the latest results. The Cossor 41MP frame generator triode has low emission causing picture rolling and lack of height.. Other valve types which will work in the frame time base are the Marconi-Osram ML4, the Mullard 104V or TT4 and the Mazda AC/P.
The T23 employs a TRF vision unit which is identical to the one used in the model T20. The secondary emission valves used in the TRF unit are well known for going low gain. When new these are fantastic valves and have a slope of almost 15mA/V From r-type.org: http://www.r-type.org/exhib/aaj0185.htm

Another fault that needs sorting out is the vertical picture shift.

DFWB.

[peter_scott]

Wow! Now that's good news.

Peter

[FERNSEH]

Hi Peter,
what's more the picture was taken with the lights on. The CRT shows no signs of having gas or any hint of low emission. Turn the brightness up fully and there is none of those effects we are all familiar with on old CRTs such as going silvery on the highlights. There is however a slight ion burn on the screen but it's hardly noticeable.

DFWB.

[Jac]

Hello David,

Een excellent result, with this CRT.
If this is indeed with the lights on, it certainly is a very bright tube!
Certainly better than any of my (working) pre-war sets.

Congratulations are in order!

Jac

[Heatercathodeshort]

Nice one David. I have made a note of those valves. I'm absolutely sure I have something. John.

Just found this Cossor 41MP hiding in the cab of my Atkinson. It's yours. Hope it is OK. J.

[Voxophone]

Great result, especially for such an old set!

One thing I'm confused about looking at that test card: won't the image (and therefore text) be reversed when viewed in the mirror lid?

[FERNSEH]

Hi Voxophone,
Artistic license. Camera picture was flipped around to show a correct test card.

DFWB.

[line sync]

Well done david , the perseverance paid off.

Robin

[Hunts smoothing bomb]

This looks to be great news indeed with that CRT David. Excellent result!

Cheers

[McMurdo]

John Logie Baird himself carried each CRT to the production line marching to the sound of the bagpipes.
Well done David after so many false starts, makes my evening's crestfallen discovery of a down to air CRM92 somewhat trivial.