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Old 27th Dec 2022, 6:32 pm   #461
FERNSEH
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Default Re: Baird T5 restoration project.

Three days ago the timebase unit was connected up to the power supply.
The frame timebase can be heard purring so that confirms the frame oscillator transformer is OK. It'll be remembered that the transformer has the extended pole pieces which perform the vertical deflection.
No line timebase operation. The Cossor 41MP oscillator valve heater is not lit up. The valve is OK so there must be a bad connection somewhere. It's an easy task to remove the timebase unit for servicing.
Today, the unused Ferranti T9-5 CRT found upstairs can be used for carrying out picture quality assessment tests before the 15" Cathodevisor 15MW4 is finally refitted. The Ferranti tube has a 4volt heater and a standard octal base. Should be OK with 5KV EHT.
Limited info available for the Ferranti T9-5.
https://www.radiomuseum.org/tubes/tube_t95.html

DFWB.
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Old 27th Dec 2022, 8:15 pm   #462
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Default Re: Baird T5 restoration project.

Keeping us all in suspense with tantalising suggestions of first light to come.

Peter
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Old 28th Dec 2022, 9:42 pm   #463
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Default Re: Baird T5 restoration project.

Quote:
Originally Posted by peter_scott View Post
Keeping us all in suspense with tantalising suggestions of first light to come.
Peter
Hi Peter,
won't be long before we see something on the 9" CRT.
Just a matter of fixing the line output valve heater supply and finding a suitable scanning coil for the Ferranti CRT. Neck is 35mm and the Baird tube is 40mm.
Also need to arrange some sort of focus magnet, either the Baird coil or a permanent magnet type.
Adaptor plate for the 9" tube was made today.
From World Radio History: https://worldradiohistory.com/UK/Pra...on-1959-06.pdf

DFWB.
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Old 30th Dec 2022, 8:05 pm   #464
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Default Re: Baird T5 restoration project.

From post No 451: T5 and T23 focus control modification. The new 10Kohm 5Watt potentiometers are of good quality manufacture but I'm considering for long term reliability replacing them with a switched resistor chain and a 1Kohm potentiometer for fine adjustment. On the T5 the fine focus adjustment will be on the upper control panel and the coarse adjustment on the timebase controls panel. On the T23 the two controls will be located on the timebase control panel.
More switched positions the better as this means more resistors in the chain for better heat distribution.


Today, I found two switches which can be used for the coarse focus adjustment.
One is a twelve position switch which will offer very fine adjustment of focus, possibly won't need the fine adjustment control.
The other is an unusual component, likely of Continental origin. Never seen a switch like this one. It has five positions so focus adjustment will be rather coarse and a series variable resistor will be required. The switch is quite large so there might not be space on the timebase control panel to accommodate it.

DFWB.
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Old 31st Dec 2022, 4:01 pm   #465
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Default Re: Baird T5 restoration project.

The 12 position. No contest.

Peter

Last edited by peter_scott; 31st Dec 2022 at 4:16 pm.
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Old 31st Dec 2022, 5:07 pm   #466
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Default Re: Baird T5 restoration project.

"The 12 position. No contest."
Hi Peter,
It's just a matter of finding eleven resistors. If I can get away without fitting a fine focus control the nearest preferred value is 470ohms.
The five position switch is too big to fit on the timebase control panel.
However, I've found a six position switch which is small enough to fit among the TB panel controls. Suggest five 820ohm resistors and a 1Kohm variable wire-wound resistor.
Attachment shows that the focus coil will need some means of raising it up to the rear of the scanning coils.

DFWB.
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Old 7th Jan 2023, 12:29 pm   #467
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Default Re: Baird T5 restoration project.

Using two pieces of 50mm diameter pipe the focus magnet is raised up close to the scanning coils. Only the line deflection coils are used as the extended frame oscillator transformer pole pieces take care of the vertical deflection. An octal socket is required for the Ferranti CRT. The 4volts for the heater can come from the vision receiver heater supply. The cathode is connected directly to the chassis and the grid to the EHT chassis and brightness control.

DFWB.
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Old 7th Jan 2023, 6:42 pm   #468
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Default Re: Baird T5 restoration project.

The Ferranti CRT T9/5 has an international octal base.
I assume the electrode connections will follow the convention of pins 2 and 7 heaters, pin 8 cathode and pin 5 for the grid.

DFWB.
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Old 7th Jan 2023, 7:05 pm   #469
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Default Re: Baird T5 restoration project.

Hi David,

According to Television Engineers' Pocket book, that is correct.

Jac
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Old 7th Jan 2023, 8:02 pm   #470
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Default Re: Baird T5 restoration project.

Hello Jac,
I'll go ahead and wire up the CRT base.
Everything is now present and correct to find out if this set can display pictures.
5KV EHT is available. 40 volts positive going video for the CRT grid.
Both timebases are working, one of the Cossor 41MP valves failed so the T23 has donated one. Power supply unit is delivering ripple free HT.

DFWB.
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Old 8th Jan 2023, 7:01 pm   #471
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Default Re: Baird T5 restoration project.

Hi David, 41MP valve waiting for you here

Ed
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Old 10th Jan 2023, 12:50 pm   #472
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Default Re: Baird T5 restoration project.

Hi Ed, Re: the 41MP, I'll give you a call today.

After wiring the CRT into the circuit the results from last night's efforts have proved disappointing, just a defocused vertical line. No horizontal deflection whatsoever. The T5 timebase unit chassis was tested in the T23 and was working fine. I accept the fact the Plessey scanning coils attached to the Ferranti tube will not be a perfect match but I would have expected some horizontal deflection. Also, the brightness control doesn't work. Image is at maximum brightness.

DFWB.
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Old 10th Jan 2023, 3:04 pm   #473
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Default Re: Baird T5 restoration project.

Hi David, out of area until Thur evening

Ed
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Old 10th Jan 2023, 5:40 pm   #474
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Default Re: Baird T5 restoration project.

Some experimenting now required with the longitudinal positions of the scan and focus coils, methinks. What's the extension pipe made of?

Steve
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Old 10th Jan 2023, 9:06 pm   #475
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Default Re: Baird T5 restoration project.

"What's the extension pipe made of?"
Hi Steve, it's 2inch diameter plastic pipe. It was used to make EHT capacitors such those fitted in the Ekco TSC1113.
Some results today. The line scanning coils were incorrectly wired, mea culpa.
After turning the CRT and scanning coils 90 degrees there is now a very small raster on the screen. The reason for that will be the wider scanning angle of the 9inch CRT, 57 degrees. Scanning power is a function the scanning angle and EHT voltage. Can't remember the formula. The scanning angle of the Cathodevisor 15MW1 must be only 45*, maybe even less?
The timebase oscillator valves are Cossor 41MP triodes. According to the Valve Museum early examples of this valve delivered 1 watt @ 5% distortion. Perhaps the later valves which are tetrodes internally connected as triodes can deliver more power?
http://www.r-type.org/exhib/aaj0046.htm
Possible replacements for the 41MP are the Mullard TT4 and the M.O. ML4.
The focus coil is faulty, the resistance is 19,000ohms. Checked the resistance of the focus coil in the T23 and the figure is 1,100ohms.
Something else to sort out before the 15" CRT is reinstalled.

DFWB.
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Old 11th Jan 2023, 9:10 am   #476
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Default Re: Baird T5 restoration project.

Great stuff David,
not far to go now
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Old 15th Jan 2023, 11:51 pm   #477
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Default Re: Baird T5 restoration project.

For test purposes a 0.47ohm is resistor connected in series with the line scanning coils.
Oscilloscope set to 5mV/division using a X10 probe.
Timebase set to 20uS/division.
Maximum current through the scanning coils is about 0.2amp. P - P.

DFWB.
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Old 2nd Feb 2023, 12:48 pm   #478
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Default Re: Baird T5 restoration project.

The Baird T5 focus coil has a resistance of 19Kohms, whereas the focus coil in the T23 is 1000 ohms. Is it possible there focus coil in the T5 has the correct ohmic value? After all, the focus control does have a limited effect on spot size on the 9" Ferranti CRT. The Cathodevisor 15MW4 CRT has a much thicker neck compared with the Cossor tube in the T23.
The fact the T23 seems to have a appetite for focus controls could be due the much lower focus coil resistance compared with the 19Kohms coil in the T5.
The T5 coil needed more ampere turns compared with the T23 coil.
The vision receiver is on the work bench again, the local oscillator has stopped working again.

DFWB.
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Old 2nd Feb 2023, 3:05 pm   #479
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Default Re: Baird T5 restoration project.

The T5 certainly does it's best to make things as difficult as possible.

Not many people would be able to pull off this restoration.

Jac
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Old 2nd Feb 2023, 9:39 pm   #480
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Default Re: Baird T5 restoration project.

Hello Jac,
the 15MW4 CRT has a 42mm neck and the Cossor CRT in the T23 it is 34mm. Both tubes operate on 5KV EHT.
Going forward in time, the 110* CRTs introduced in 1958 the neck diameter was reduced to 28.5mm from 38mm in earlier 70 and 90* tubes.
Measures to reduce the scanning power required by wide deflection angles.
The scanning angle in the Cathodevisor tube must be only 30 degrees or so.

DFWB
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