Re: Baird T5 restoration project.
 

Hi John,
Funny you should mention 15" narrow deflection tubes. I'm considering fitting the Cossor tube you gave me in the T23. My friend Kevin called in today and he suggested making a new adaptor plate to mount the tube in the Baird. The Cathodevisor CRT in the T5 is the most fearsome tube I've ever had to remove from a TV set. Close runners up in the scary stakes has to e your 15" Emiscope 3/6 and the Mazda CRM151, but what about that 16" tube that was fitted in the pre-war GEC BT8161?

DFWB.

Re: Baird T5 restoration project.
 

The purpose of the resistor in series with the diode is to isolate the diode's capacitance from the video signal. If it is too large the restorer's effectiveness is diminished. The typical value RCA chose was around 10k to 47k as I recall, it needs to be at least as big as the anode resistor in the plate of the video output valve and not much bigger in value. Maybe, looking at the photo you posted, its a 22k not a 220k ? Check it on the meter, if it reads 200k, maybe its a gone very high 22k ?

Re: Baird T5 restoration project.
 

I have been thinking about this remark.

The spacing between the anode and grid inside the tube in the CRT gun structure is very wide, quite different between say the heater & cathode or grid assembly and cathode which are closely spaced.

Not only that, inside the vacuum environment tube, unless there was a lot of loose internal aquadag, which it may not have, it is unlikely any leakage would develop between the lead out wires at the pinches, although some form of metal vapor could possibly have condensed there, but if it was getter overspill you would probably easily see it.

I think it is much more likely the leakage between the anode and grid connections is on the outside surface of the CRT, in the base, where the lead wires exit the bulb, I have seen this before.

What happens is the lead out wires corrode over time and it creates a subtle greenish film on the glass between the wires where the pinches are and between where they exit the base of the neck. This film is not soluble in contact cleaner.

If it is this problem, it needs to be sprayed with de-ionized water and the glass around the lead out wires gently stroked with a soft tool, a wooden cut down match end attached to a handle, being careful not to touch or bend the wires where they exit the bulb, as they can be very fragile, possibly corroded and break off. Then dry it with a hair dryer on low heat.

I'm not sure what the base on this tube is like or how easy it could be to remove if that was necessary to check it. Obviously before attempting it you would have to be 100% certain each wire was de-soldered and free from the pin as those lead out wires are easily broken when they are aged. And if they are going to break it will tend to happen close to the glass pinch, then its a real problem.

Re: Baird T5 restoration project.
 

I was thinking about that GEC 6101 16" glass tube just yesterday! They are very rare and I think 70 degree, maybe aluminised, so the picture would be poor if installed in the T5.
The Mazda CRM 151 again requires high EHT but is very narrow angle. 15" tubes are a problem and always were. Something always turns up! John.

Re: Baird T5 restoration project.
 

Argus25 wrote: "The purpose of the resistor in series with the diode is to isolate the diode's capacitance from the video signal. If it is too large the restorer's effectiveness is diminished. The typical value RCA chose was around 10k to 47k as I recall, it needs to be at least as big as the anode resistor in the plate of the video output valve and not much bigger in value. Maybe, looking at the photo you posted, its a 22k not a 220k ? Check it on the meter, if it reads 200k, maybe its a gone very high 22k ? "
The resistor in series with the WX6 is indeed 22Kohms and is well within tolerance for such an old component.
Yesterday evening the EHT cable to the tube anode was disconnected and voltages and waveforms on the CRT grid checked to see if there would be any changes. Results were just the same as with EHT. So it's has to be leakage between the grid and cathode that's causing the brightness control and DC restorer not to work correctly.
The CRT will be taken out later today and that wire link between the cathode and heater will be removed. The tube cathode connection will be free for the brightness control as it is in the model T20.

DFWB.

Re: Baird T5 restoration project.
 

Just to compound the horror of this set the tube won't come out. After removing the safety glass and mask pull off the anode connector on the CRT cone. Disconnect the three wires on the tube base. Disconnect the line scanning coil plugs. The tube should lift out, but it doesn't, and of course you can use any form of force when handling these fragile tubes.
This job is not going very well.

DFWB.

Re: Baird T5 restoration project.
 

There is an insulating ring between the focus coil and the line scanning coils. See attachment.
It's possibly this part that is preventing easy removal of the tube.

DFWB.

Re: Baird T5 restoration project.
 

Of course the tube won't come out. The metal adaptor plate must be unscrewed and using this device lift the tube straight up and away from the cabinet.
Let's see if that works.

DFWB

Re: Baird T5 restoration project.
 

It would seem you have created a very large type of Meccano jigsaw puzzle but, I am sure your many years of servicing will get it sorted. Probably when first built the cabinet was built around the tube etc?

Re: Baird T5 restoration project.
 

The tube is at last out from the cabinet. Now I can remove that wire link between the heaters and cathode.

DFWB.

Re: Baird T5 restoration project.
 

Hi David,
As awful as the tube mounting assembly looks now it was far worse when I acquired the set in 1993. The focus coil was mounted on three long pieces of 2BA threaded rod, the whole assembly was, well, just wobbly. Without delay wood spacer blocks were made to raise up the focus coil so that it was close to the line scanning coils. It's difficult to believe that this CRT substitution job was done by Baird Television Ltd. Or was it?

The tube was refitted this morning and the set is ready to be tested.

DFWB.

Re: Baird T5 restoration project.
 

At last I've found the 9mm plywood needed to match the veneered surfaces on the original side panels. So yesterday I set about making two new panels. The attachments show the surfaces will require more dark wood stain to look like the originals.
It will be recalled the side panels made earlier this year are a perfect fit but it was all too obvious these were nothing more than dark stained plywood, not a good look.
After this project is completed we'll find that there will be almost enough spare cabinet parts to make another T5 or T23.

DFWB.

Re: Baird T5 restoration project.
 

They look nice.

Peter

Re: Baird T5 restoration project.
 

Well done David, it's getting there, those 15" CRT's scare the cr:censored:p out of me!

Cheers

Re: Baird T5 restoration project.
 

Hi Peter, I've applied more wood dye to the panel surface and as the attachment shows it's starting to resemble the original part.

Hi Lee, it's a scary business removing and refitting those 15" tubes. In my T23 it's easy to lift out the tube but refitting it is a real hairy job. The tube bowl is placed on a special metal plate which must be aligned with the four threaded spacer rods and these never line up first time so you are holding the tube with one hand and fiddling about with the rods with the other. Not a pleasant experience.

But if you think 15" and 16" all glass tubes are scary just check out the 20" Dumont tube.
From the ETF: http://earlytelevision.org/dumont_20AP4.html

DFWB.

Re: Baird T5 restoration project.
 

Hi David,
those bits of wood for the side panels are a real find. The veneer pattern is even similar to the original panel shown in your picture.

Cheers
Andy

Re: Baird T5 restoration project.
 

Hi Andy,
Those new side panels have got the cabinet renovation restarted. Now the newly made front panels must be veneered, that's no problem as veneer sheets are readily available.
As for the T23, the CRT has gone dim, so before it was too much brightness, now there isn't enough.

DFWB.

Re: Baird T5 restoration project.
 

It was suggested to me that the cabinet top panel could be salvaged. I had my doubts but was willing to have a go. As the first picture shows the plywood panel is in just same bad state as all the others.
I was not entirely satisfied with the first attempt at making a new top panel so a new one is being made. The second picture shows the first stage of the construction of the new panel.
The book matched veneer strips arrived yesterday so a start can be made applying the veneers to the new front panels.

DFWB.

Re: Baird T5 restoration project.
 

Good evening David,

Quite a big job!
Luckily in expert hands.

Jac

Re: Baird T5 restoration project.
 

Hello Jac,
The first attempt to make the top panel didn't go very well. The router tool kinda went wild and shaved off too much wood in places. I did some corrective work using wood filler but this job has to be right. All the new parts must replicate the originals.

DFWB.

Re: Baird T5 restoration project.
 

The old top certainly looks unsavable but the problems of reproducing it are also very real and no doubt give others the same shudders that I get at the thought of having to do it.

Peter

Re: Baird T5 restoration project.
 

Well here goes. The screen aperture will be cut out later today.

DFWB.

Re: Baird T5 restoration project.
 

Are you using MDF for the screen aperture? Routing the recess for the glass would be a PITA in ply.

Re: Baird T5 restoration project.
 

It's 12mm plywood, the same material as the original was
The next stage is to make the chamfered edges of the screen aperture.
Then, after that's done make the recess for the safety glass.
The router tool will be used for the last two operations.

DFWB.

Re: Baird T5 restoration project.
 

"The next stage is to make the chamfered edges of the screen aperture."

That job was done this morning so the next task is to use the router tool make the 1/4 inch deep recess for the implosion protection window.

DFWB.

Re: Baird T5 restoration project.
 

That's the top panel recreation almost finished, the final stage will be the application of veneers to the upper surface.
No idea what that piece of 90* angle steel came from but it made an excellent guide fence for the router tool.

DFWB.

Re: Baird T5 restoration project.
 

The new top panel is test fitted along with the control board and lower front panel. These are the panels which must be veneered.

DFWB.

Re: Baird T5 restoration project.
 

Excellent work, David. I've been following your progress with great interest. How confident are you with the veneering? That always seems a bit scary to me! What finish will be applied over the veneer?

All the best
Nick

Re: Baird T5 restoration project.
 

Hi Nick,
In the event that the veneering of the panels doesn't turn out too well I've made duplicates of all the cabinet sections. The veneers supplied to me are book matched so the completed panel surfaces should resemble the originals.
The first cabinet part to receive attention will be the top panel starting with applying veneers to the chamfered edges of the CRT screen aperture.

DFWB.

Re: Baird T5 restoration project.
 

Hi all,
I recently obtained a technical book which contained some detail of the early dual standard T5 (I've been after such info for years).
Compare with Peter's diagram in post 155 on page 8 of this thread.
Note that a number of controls are in different places and somehow the two lock controls are in fact one instead.
The set I restored many years ago was made in September 1936, but had obviously been converted in house to single standard (maybe before it was sold?). There were telltale marks where the extra pots had been bolted.
Moving the control markings would have been easy as the engraved plastic labels are simply held in place by the retaining nuts on each control pot.

Cheers
Andy

Re: Baird T5 restoration project.
 

That's very interesting Andy. There is so little information about the dual standard configuration in the T5. Do you have circuit details? Also, what functions do the three (inaccessible) controls have on the bent over top of the control panel?

So the two blanked off holes were Line Speed A and Line Speed B.

Frame Speed A became 405 Frame Speed
Frame Speed B became 405 Line Speed.
System Switch became Picture Width.

Thanks,

Peter

Re: Baird T5 restoration project.
 

Hi Peter,
I wish I did have the dual standard circuit details. The circuits I have been made on a Bander Duplicator (I think that is what it was called) and were sent to the original owner of the T5 that I restored. They were sent by Bush radio after the war; the timebase circuit states "redrawn 19-2-51" and gives no clue of the dual standard arrangement.
Two of the top controls are coarse line hold and frame hold and the third one is coarse frame height. The set I restored definitely had something in the fourth spot originally.

Going back to the two coarse controls hold, these alone had enough range to get the the Baird timebase frequencies of 25Hz and 6KHz with no other component changes required. Were there four hold coarse controls before (if so was the no coarse height?) or was it only either the line or frame hold that had two coarse settings?
All still a bit of a mystery.

Cheers
Andy

Re: Baird T5 restoration project.
 

Thanks Andy. In the EMI timebases there were resistor changes to alter the blocking oscillator frequencies and feedback capacitor changes at the output stages to compensate for the amplitude changes so I guess the T5 would have something similar.

Peter

Re: Baird T5 restoration project.
 

Not a lot of help but I have attached two scans of the original Baird T5 blue print timebases. They are very large and my scanner is A4. dated December 1936 but stamped 1938. Interesting to note the deletion of the 'switch' in Jan 1937. Hope these help. Regards, John.

Re: Baird T5 restoration project.
 

Thanks John. It's just general curiosity on my part rather than a need to know but I find it all very interesting. Although the changes are listed it's strange that they don't reference the components.

Peter

Re: Baird T5 restoration project.
 

Wouldn't be surprised if the 1935 T5 development sets were designed for the 240 line 25 f.p.s. system only and later adapted for dual standard operation.
Baird Television Ltd demonstrated an earlier mirror lid model which might have been the basis of the T5. Pictures of such sets can be found on the internet.
Even J.L.Baird himself conceded that the cathode ray tube was the only practical means of displaying high definition pictures.

The attached picture was posted up at the beginning of this topic.
Compared with the production sets the 1935 prototype doesn't seem to have as many preset controls behind the door.

DFWB.

Re: Baird T5 restoration project.
 

Going on that photo David you could very well be right. There don't appear to be many controls in the cupboard. Nothing obvious in the "Standards Switch location.

Peter

Re: Baird T5 restoration project.
 

Not quite the same thing but a couple of years ago I re-veneered a hifi cabinet. Here's a link to the trials and tribulations. It's not that difficult if you plan and execute very carefully.

https://www.vintage-radio.net/forum/...d.php?t=130650

Re: Baird T5 restoration project.
 

Hi Peter,
The 1935 prototype has the big 15" CRT. BTL experimented with even bigger tubes. Cossor made an electrostatic 14" tube for the model 137T.

DFWB.

Re: Baird T5 restoration project.
 

Hi Steve,
That's an excellent job. Now that last week's Freeview retuning calls have been done this week should be free to make a start on the three panels.
Starting with CRT aperture panel.

DFWB.

Re: Baird T5 restoration project.
 

I see in TV&SWW in March 1935 they have the 15" CRT in a different cabinet and described the picture as black & white with no flicker.

Peter

Re: Baird T5 restoration project.
 

Peter, your post inspired me to look up details of the television transmissions of the time from the Baird station at Crystal Palace, which pre-dated the BBC. They were on 180 and 240 lines. Vision: 42.8MHz (10kW). Sound: 35.3MHz.

http://www.ambisonic.net/bairdcp.html

Steve

Re: Baird T5 restoration project.
 

Hi Steve,

I see from the ambisonic site that the T5 was equipped by 8th November 1935 for dual standard 240/405 operation so perhaps I didn't interpret the photo with Sydney Moseley correctly after all and that in the period from February to June 1935 Baird's Crystal Palace Transmitter was radiating 180 line transmissions.

Peter

Re: Baird T5 restoration project.
 

A few scans from TV&SWW December 1936.

Re: Baird T5 restoration project.
 

Hi John,
I notice the cabinet style in those adverts in the alternative to the one that David is restoring. It has no vertical flutes on it, it has two decorative horizontal stripes and a "V" shape inlaid into the front veneer.
This is like David's own T23. I know that an American collector owned a T5 with this style of cabinet at one time.

Hi Peter,
I like the look of that early 15" set - nice and cubist :)
I wonder about the flicker free claim. Could it be that the earlier tube had a bit of lag built into the phosphor mixture? I've yet to establish the difference between the 15MW1 and 15MW2 crts, maybe that was it? Also the question of phosphor colour comes into play as well. We know that the EMI sets were first to be supplied with green screens, as often shown by the crossed out early tube type number on the internal labels (though it would seem that white phosphor became available to EMI just in time...).

Cheers
Andy

Re: Baird T5 restoration project.
 

Hi Andy,

Yes, a longer persistence phosphor with its rather slow response to moving objects might have been more acceptable than the flicker. I wonder if the after glow would also be white? Or would it be yellow or green perhaps?

Peter

Re: Baird T5 restoration project.
 

"Could it be that the earlier tube had a bit of lag built into the phosphor mixture? I've yet to establish the difference between the 15MW1 and 15MW2 crts,"
Hi Andy,
The CRT in the T5 the subject of this discussion is a Cathodevisor 15MW4. A post-war replacement?
I believe the formulation for the white phosphor arrived just in time for the high definition television service in 1936. Even so wasn't the Emiscope 6/1 a green screen tube?

DFWB.

Re: Baird T5 restoration project.
 

Yes it was David, like the 6/3.

Ad in the September 1937 issue of Television and SW world:

Attachment 193950

Jac

Re: Baird T5 restoration project.
 

That's an interesting ad, Jac. I wonder what the difference was between the 6/4 and the (later?) 6/6?

Steve

Re: Baird T5 restoration project.
 

Steve, it certainly would be very interesting to have more info on the pre-war EMI tubes!

No data book I have (but I don't have that many...) mentions the 6/4.

But certainly data must be in possession of someone on this forum.
Let's hope something turns up!

Perhaps "Catkins" (on this forum) might have a relevant data-book. He has posted this photo of data on the 3/1 and 3/2 (I hope it is OK to mention this here):

Attachment 193953

Jac