UK Vintage Radio Repair and Restoration Discussion Forum

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-   -   Baird T5 restoration project. (https://www.vintage-radio.net/forum/showthread.php?t=152005)

FERNSEH 16th Jan 2020 8:24 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
That's the other side panel re-veneered. The left side panel will be the one with the on-off switch.

DFWB.

FERNSEH 25th Jan 2020 9:29 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
Assembly of the side panels has started. The Attachment shows the inside of the right side panel.

DFWB.

line sync 26th Jan 2020 10:08 am

Re: Baird T5 restoration project.
 
Keep up the good work david , your doing a great job.

Robin

FERNSEH 29th Jan 2020 4:25 pm

Re: Baird T5 restoration project.
 
2 Attachment(s)
First picture. That wasn't too difficult after all. Today I refitted the timebase controls door ball catch to the front panel.

Second picture.
Over the weekend the left side panel was reassembled. Also the cabinet floor plinth. Not too sure about that one and it's possible a new one might be have to be made. The old plinth had received some attention from the woodworms.

DFWB.

mark pirate 30th Jan 2020 5:02 pm

Re: Baird T5 restoration project.
 
Quote:

The old plinth had received some attention from the woodworms.
No point in risking it, after all the hard work you have put in the last thing you need is a re infestation!
:beer:
Mark

FERNSEH 30th Jan 2020 9:21 pm

Re: Baird T5 restoration project.
 
"No point in risking it, after all the hard work you have put in the last thing you need is a re infestation!" Mark.

Hi Mark,
It's an easy enough part to replicate. Took a look at the reassembled plinth this morning and it is a horrible looking thing, and as you say there might well be some wee things living in it.

DFWB.

beery 31st Jan 2020 1:46 pm

Re: Baird T5 restoration project.
 
Quote:

Originally Posted by FERNSEH (Post 1212289)
The old plinth had received some attention from the woodworms.

DFWB.

Well certainty the plinth has to be very strong on such a heavy set. Maybe a new one would be safer even just from a structural point of view.

Cheers
Andy

FERNSEH 1st Feb 2020 4:49 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
At last it's beginning to look like a Baird T5 again.

DFWB.

FERNSEH 7th Feb 2020 9:39 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
Final assembly of the cabinet started today. The cabinet parts shown in the attachment have been glued into position. The timebase controls door opens and closes as it should.

DFWB.

FERNSEH 8th Feb 2020 10:18 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
The left side panel was fitted today.

The cabinet floor was test fitted but will not be screwed and glued into position until all the guide blocks for the two power supply units are fitted.

DFWB.

FERNSEH 12th Feb 2020 4:56 pm

Re: Baird T5 restoration project.
 
2 Attachment(s)
It's the new cabinet floor that is receiving attention to today. With a little fettling it's now a perfect fit. But before it is screwed and glued into position the wooden blocks which locate the two power units must be fitted first.
The cabinet floor certainly stiffens up the cabinet structure.

DFWB.

FERNSEH 14th Feb 2020 1:20 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
I now have to determine the exact positions for the Power supply units and the central wooden block that supports the focus coil assembly.

DFWB.

FERNSEH 22nd Feb 2020 9:49 pm

Re: Baird T5 restoration project.
 
4 Attachment(s)
Real progress today. At last this is for real and not test fitment of parts.
Apart from the blocks which are screwed and glued into position and used to locate the panels all the other parts are removable to do any servicing or replacement.
When did you ever see a spirit level used to repair a TV set?

DFWB.

Freya 22nd Feb 2020 10:08 pm

Re: Baird T5 restoration project.
 
A fine achievement so far, keep it up :thumbsup:

FERNSEH 23rd Feb 2020 12:49 am

Re: Baird T5 restoration project.
 
Hi Steven,
The job for next week will be to drill holes in the upper panel for the controls and tuning scale. Also, more cabinet trim parts to fit. It really is looking like a T5 now.

DFWB.

FERNSEH 26th Feb 2020 5:05 pm

Re: Baird T5 restoration project.
 
2 Attachment(s)
More progress today. The control panel assembly is complete and has been test fitted into the cabinet. Not much more to do to the cabinet now.

DFWB.

peter_scott 26th Feb 2020 5:40 pm

Re: Baird T5 restoration project.
 
It's going to look very good!

Peter

FERNSEH 27th Feb 2020 10:17 am

Re: Baird T5 restoration project.
 
2 Attachment(s)
Hi Peter,
There is almost enough spare parts left over to construct another T5. Just have to go looking for another wreck to rebuild.
The loudspeaker doesn't look very nice but it does work OK. Makes a good sound.

DFWB.

FERNSEH 27th Feb 2020 5:48 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
The cabinet mirror lid was one of the many original parts which was salvaged and refurbished.

DFWB.

Heatercathodeshort 27th Feb 2020 9:53 pm

Re: Baird T5 restoration project.
 
What an epic journey! The men in white coats are just around the corner waiting to pounce. The cosmetic parts of a restoration is always the most difficult.
Seriously, well done! John.

System A 27th Feb 2020 11:00 pm

Re: Baird T5 restoration project.
 
Hi David, what a superb job you're making of this restoration.
I'm throughly enjoying this thread.
Regards.
Gary

mark pirate 28th Feb 2020 11:39 am

Re: Baird T5 restoration project.
 
I am in awe at your cabinet skills David, Looking forward to see the finish go on!
:beer:
Mark

stevehertz 28th Feb 2020 12:55 pm

Re: Baird T5 restoration project.
 
This is a critical stage now as all that excellent woodwork needs to be topped with appropriate coloured lacquers and/or the use of stains beforehand. I once completely stripped a small Marconi radiogram. Once stripped, the various wood panels and edhe mouldings were different coloured woods. It was a hell of a game trying to get finishes to match up. I didn't quite achieve it! Best of luck David, I'm sure you're going to amaze us again.

Panrock 28th Feb 2020 2:13 pm

Re: Baird T5 restoration project.
 
First, a big (and humble) "well done" for what David (DFWB) has achieved here. Not many would have taken this job on. Still fewer managed to obtain such a good result.

There are probably as many opinions on the subject of finishing as there are people here. As I've said before, I personally am opposed to the use of stains for tinting purposes. By the thirties and forties, coloured toning lacquers were the order of the day for the mass marketed radio industry, and using these again will be good for originality. Moreover, when using a spray gun, their density can be controlled by mixing with the filler/base coat. One advantage here is that you gain more grain pit filling, and another from using toner is that the colours of adjacent (different) sprayed panels will tend to converge.

I think David said he is going the French Polish route here, however. I'm sure the final result will be most impressive.

Steve

FERNSEH 28th Feb 2020 4:21 pm

Re: Baird T5 restoration project.
 
Panrock wrote:
"There are probably as many opinions on the subject of finishing as there are people here. As I've said before, I personally am opposed to the use of stains for tinting purposes. By the thirties and forties, coloured toning lacquers were the order of the day for the mass marketed radio industry, and using these again will be good for originality. Moreover, when using a spray gun, their density can be controlled by mixing with the filler/base coat. One advantage here is that you gain more grain pit filling, and another from using toner is that the colours of adjacent (different) sprayed panels will tend to converge."

I think David said he is going the French Polish route here, however. I'm sure the final result will be most impressive.


Hi Steve,

rather than French polishing the completed cabinet I'm considering passing the final finishing to a local firm to have it spray painted just as it was done in 1937 when the set was made. A very dark lacquer was used for the original finish, the norm for those times. It's something to be discussed with the owner of the set.

DFWB.

FERNSEH 28th Feb 2020 4:31 pm

Re: Baird T5 restoration project.
 
Quote:

Originally Posted by stevehertz (Post 1221015)
This is a critical stage now as all that excellent woodwork needs to be topped with appropriate coloured lacquers and/or the use of stains beforehand. I once completely stripped a small Marconi radiogram. Once stripped, the various wood panels and edhe mouldings were different coloured woods. It was a hell of a game trying to get finishes to match up. I didn't quite achieve it! Best of luck David, I'm sure you're going to amaze us again.

Hi Steve,
on the previous page the picture of the almost completed cabinet clearly shows the different coloured woods used during the assembly. That's why I'm sure all those mass produced radios were always in a dark finish. Helps to hide some of the imperfections as well. How often have you seen that after stripping off the lacquered surfaces off old radios?

DFWB.

Magpie66 28th Feb 2020 9:53 pm

Re: Baird T5 restoration project.
 
When we rescued this T5 it was full of woodworm and dust and was only held together by the veneer and varnish. Now look at it. A piece of history brought back to life. After we acquired this Television we were unsure what to do with it as it was in such a bad condition but thanks to feedback from various members on this forum we decided to have it renovated and so many people recommended David.
You have done a grand job and I donít think we could have chosen a better person to complete the work.
Keep it up.
Ant and Tina

stevehertz 29th Feb 2020 12:00 pm

Re: Baird T5 restoration project.
 
Quote:

Originally Posted by FERNSEH (Post 1221068)
Panrock wrote:
"There are probably as many opinions on the subject of finishing as there are people here. As I've said before, I personally am opposed to the use of stains for tinting purposes. By the thirties and forties, coloured toning lacquers were the order of the day for the mass marketed radio industry, and using these again will be good for originality. Moreover, when using a spray gun, their density can be controlled by mixing with the filler/base coat. One advantage here is that you gain more grain pit filling, and another from using toner is that the colours of adjacent (different) sprayed panels will tend to converge."
I think David said he is going the French Polish route here, however. I'm sure the final result will be most impressive.

Hi Steve,
rather than French polishing the completed cabinet I'm considering passing the final finishing to a local firm to have it spray painted just as it was done in 1937 when the set was made. A very dark lacquer was used for the original finish, the norm for those times.
It's something to be discussed with the owner of the set.

DFWB.

Definitely the way to go. Nonetheless, a lacquer - even a dark one - can only 'equalise' the colour of woods underneath to some extent. Personally I would consider using stains on the bare wood to 'help' the process prior to spraying, and that would also mean that you would not have to use such a dark lacquer. As I recall, the T5 was not finished in a dark colour, more of a medium brown.

The original lacquer would have been cellulose. Not sure if you're able to get someone to use that, but that's what it was.

FERNSEH 3rd Feb 2021 6:36 pm

Baird T5 restoration project.
 
2 Attachment(s)
It's almost a year since I posted up anything about this set.

https://www.vintage-radio.net/forum/...152005&page=17

Work on the set continues.
The cabinet is ready for the final finish to be applied to the surfaces.
However, the plan was to use the original CRT mounting board, but now I'm having second thoughts about using it and the replica board is to be fitted instead. The CRT bulb sits on this board and the hole has to be chamfered to the correct angle to accommodate the shape of the tube. A special router tool was bought for this purpose. A piece of 9mm plywood with a 7 inch diameter hole cut out in it was to used so that the wheel on the router tool can be guided just away from the edge of the hole in the CRT board.
That job has been done and now I've turned my attention to the replica focus coil mounting board. Again the same router tool was used to make the chamfered edge in the four inch hole for the focus coil plate.

DFWB.

FERNSEH 5th Feb 2021 8:06 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
It's getting close to the stage where a CRT must be fitted in the cabinet to confirm that all the new parts are in the correct positions. But it would be certainly unwise to use the original tube for the purpose. Once that component has been installed it stays in unless other reasons arise. With TV sets having a 12" diameter tube I have a down-to-air CRM121 which is used to determine the installation arrangements before a good tube is fitted. An example is my Beau Decca TV recreation.

The Cathodevisor CRT has a 41mm neck diameter. A wound steel tube is fitted over the CRT neck, the line scanning coils are fitted close to the flare of the bulb and the frame scanning coils are mounted on the CRT mounting board.

The dummy tube won't be a CRT but a length of tubing attached to a wood disc which will be placed in the position where tube bulb rests on the upper board. The attached picture shows a piece of plumbers pipe which is almost the same diameter as the CRT neck.

DFWB.

FERNSEH 8th Feb 2021 10:05 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
The 15MW4 CRT is a post-war replacement. Certain modifications were required to install the tube including an octagonal shaped wood adaptor block to move the position of the focus coil.

The pre-war tube was the Cathodevisor 15MW1 or 15MW2. A 15MW3 was made but this was a post-war tube which was similar to the Mazda CRM151.

DFWB.

beery 9th Feb 2021 6:15 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
Hi David,
That's great.
I've now received the mouse eaten line output transformer.
I will be attempting a simple repair of the outer layer rather than full rewinding.
First of all I need to remove the lamminations, which shouldn't be too hard because these transformers were never varnished.

I will report back on my progress at this end.

Cheers
Andy

beery 19th Feb 2021 10:13 am

Re: Baird T5 restoration project.
 
4 Attachment(s)
Hi all,
I've now repaired the Baird T5 line output transformer.

The outer (synch injection) winding had been chewed by some wee beastie.

I took off the laminations to get to the windings. The laminations are T and U stampings, which were alternatively arranged as in a mains transformer, this is unusual in a line output transformer where we would expect the laminations grouped together and gapped.
The outer layer consisted of 10 turns of 36SWG (0.19mm) SSC (Single Silk Covered wire) which was no enamelled. A few of those turns were broken in the same place.
I unwound the damaged layer and found 33 healthy turns. 3 turns from this layer were unwound to provide a good lead in to a wire splice. I then covered the good layer back up with craft tape, cut back the wire to about 1 turn and spliced on some new 36SWG enamelled wire. I then added another 12 turns to get back to where we were before. As it was the final layer, there was space to spread the wire out a bit, which would give more even support to the lead out terminal.
Some transformer tape was used to stabilise the windings, but I was careful not to let it go too near the edges of the craft paper. So that the bright yellow tape would be hidden when the repair was completed.
A layer of craft tape was added and the terminal was connected and secured with fibre glass tape. More craft tape was added over the top.
Finally about half of the original varnished cloth outer insulation was glued back on. The damaged insulation on the top part of the transformer was replaced by similar material that was recovered from a scrap GPO 3000 type relay.
I will post the transformer back to David next week.

Some observations on the transformer design:-
Very unusually proportioned laminations made for a narrow, but thick coil, i.e. many layers, each with a small number of turns - this makes for a transformer with low inter-turn capacitance, great for responding to the rapid flyback of the line scan. Single Silk Covered wire has a slightly larger overall diameter than enamelled copper wire and this will have assisted in reducing the winding capacitance. For VHF coils often Double Silk Covered wire was used in pre-war sets.
Anyway, the use of a narrow but tall winding Single Silk Covered wire can be considered an alternative to wave winding a line output transformer. As I had only to replace 12 turns on the outer layer then enamelled copper wire slightly spaced out will be fine. If I had to rewind the whole thing then another approach would have to be considered. Synthetic silk covered wire is available, but it is very very expensive.

Cheers
Andy

peter_scott 20th Feb 2021 8:55 am

Re: Baird T5 restoration project.
 
A really beautiful repair.

Well done!

Interesting construction too.

Peter

ChristianFletcher 20th Feb 2021 8:59 am

Re: Baird T5 restoration project.
 
Yes I agree that transformer repair is very impressive

FERNSEH 20th Feb 2021 4:29 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
Hi Andy,
many thanks for doing a superb job, it looks great. As soon as it arrives I'll set about restoring the timebase unit. It's the only unit that hasn't been been fully checked over. The T23 can be employed as the test receiver, assuming of course the CRT can be made to work again.
The attachment shows the circuit diagram of the self-oscillating line timebase.
The line scanning coils are fitted on the CRT neck in the usual manner and the frame timebase employs that clever arrangement in which the oscillator transformer has those laminations which extend out to the neck of the CRT.

DFWB.

beery 20th Feb 2021 5:40 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
Hi David,
can you measure the scan coil resistances for completeness? It would be interesting to compare them with my Garrick which is a development of the T18.

I've measured the resistances and inductances of the windings on the T5 line output transformer. They are:-
1st winding, Brown leads, 322ohms, 2.5H
2nd Winding, Brown leads, 59 ohms, 635mH
3rd winding, Yellow leads, 55 ohms, 406mH

The leads for the start of each winding emerge from the top of the transformer and the leads for the end of eacj winding emerge from the bottom of the transformer. As the transformer is mounted on its side in a drop-through style then it really does not matter which way round it goes. Well it does now of course because the wires having been cut to length when the set was made will now only fit one way! Anyway, the idea of having all windings start on one side and finish on the other is very clever in its simplicity and also fool proof.

Cheers
Andy

FERNSEH 20th Feb 2021 7:27 pm

Re: Baird T5 restoration project.
 
Hi Andy,
I've checked the DC resistances of the line scanning coils in the T5 and T23, both read 29ohms.
There is a 50mfd DC blocking capacitor in series with the scanning coils. It is safe to suggest the waveform at the grid of the 41MP triode is negative going as one would expect in an oscillator, the presence of the series capacitor will supply the coils with a sawtooth waveform symmetrical about zero.
All the Cossor 41MP triodes I've come across in Baird TV receivers are triode connected tetrodes or pentodes. Very early 41MP valves were true triodes.
High peak voltages are present at the anode of the line output valve, hence the ceramic valveholder.
Some info about the Cossor 41MP: https://www.radiomuseum.org/tubes/tube_41mp.html

DFWB.

FERNSEH 27th Feb 2021 10:09 pm

Re: Baird T5 restoration project.
 
1 Attachment(s)
The rewound line output transformer will be refitted in the T5 timebase unit and testing procedures will be carried out in the T23. But first the T23 must be returned to working order. It will recalled the set is having problems with the Cossor CRT. The plan is to modify the CRT brightness control circuit to the arrangement employed in the Baird T18 and T20.
In the original T5 circuit the brightness control is in the video DC restorer. The negative voltage present at the cold end of the EHT transformer secondary is adjusted by the brightness control to provide the sync tip reference.
In the T18 the brightness control varies the cathode voltage of the CRT. The positive going video is AC coupled to the grid of the CRT. The DC component of the video is lost. It should be possible to retain the DC restorer diode with the negative going sync tips clamped to chassis potential.
The attachment shows the T18 CRT circuit.

DFWB.


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