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Old 29th Jul 2019, 7:59 pm   #81
FERNSEH
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Default Re: Baird Garrick

The Fernseh DE6 didn't employ the Baird patented frame timebase transformer with the extended pole pieces. The scanning coils look like a conventional type. Chassis construction different from the Baird T5.
Link to a topic about the DE6: https://www.vintage-radio.net/forum/...ad.php?t=42854
A picture of the internals of the set appears in post No.9.

DFWB.
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Old 29th Jul 2019, 9:09 pm   #82
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Default Re: Baird Garrick

David,

Darius' reference was to the Fernseh HPE 5R. https://www.earlytelevision.org/fernseh.html

HPE 5 R (1939). Projection set produces a 17" by 20" picture on a directional screen attached to the lid. This set appeared in a 1939 magazine and was identified as being at the 1939 Berlin Exposition. It was to be sold for about $225. It uses Baird's patented vertical deflection. Baird was a member of Fernseh A.G. (Information courtesy of Darius-Karim Mottaghian-Milani).

Peter

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Old 1st Aug 2019, 12:40 pm   #83
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Hi all,
Last night I drew up the circuit of the timebase section of the Baird Garrick as it currently is, with flyback EHT. See the attached PDF.

The focusing arrangement is interesting with a constant current sink which works by comparing the voltage across VR6 with a 100V reference provided by neon stabiliser V1. The grounded grid of the SP42 looks very odd at first.

Also note the DC restoration diode on the CRT grid, however no such diode appears on the cathode circuit. Remember that the black and red wires from the vision receiver provide a negative and a positive video output.

When the set was adapted to flyback EHT, VR4, L3 and C4 were added together with V8 and C17.

I don't know the actual value of wirewound screen feed resistor R8 as it has overheated, loosing all of its outer cement and causing the resistance wire to spring out. I will attempt to measure what is left.

The frame circuit is very similar to the Baird T18.

Cheers
Andy
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Old 7th Aug 2019, 1:08 pm   #84
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Default Re: Baird Garrick

Hi all,
in the circuit of the timebase that is in my last post, you can see that the screen feed resistor of the line output valve (R8) is labelled 3K3? The reason why becomes clear when you look at the attached photo of it...

Anyway, you can just make out that the very left hand part of this resistor is still intact. By measuring its resistance and width I was able to extrapolate it. This produced a value in the range of 6K to 8K, so I have ordered a 6K8 14W resistor to try.
It is interesting to note that the screen feed is not decoupled unlike in the Baird Countryman (which is probably where the flyback EHT line output transformer comes from). The pre-war T18 circuit is of no use here either as it uses a triode for the line output.

Cheers
Andy
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Old 29th Aug 2019, 11:01 pm   #85
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Default Re: Baird Garrick

Hi all,
I've been re-stuffing the waxies on the underside of the timebase chassis of the Baird. Now I turn my attention to the electrolytics...
The first photo shows a metal bodied electrolytic who's can might have been shorting against the tag next to it. This would be one reason for the burn up in the line output stage. Anyway, it is not original, so I set out to make up a cardboard one copied from others in the set.

I obtained a spare Plessey capacitor of the right size and different value. First I removed the label and pulled off the lead out wires by waggling them until they snapped.
Then (picture 2) I drilled a 0.8mm hole just under the rivet on each end cap.

The capacitor is then sliced open (picture 3) and the insides removed.

A new capacitor is fitted with extended lead out wires which are threaded through the holes that were drilled in the end caps (picture 4).

The end caps were then glued in with UHU, the cut slot was also glued with UHU and a single layer of sellotape was wound round to hold it together whilst the glue set.
The tape was left on, but covered up by covering with a lablel of the correct value which I had made by colour photocopying it from one of the other capacitors in the set (which was also rebuilt).

Finally the capacitor was put back in place of the metal bodied one. You can see this at the top of picture 5. The capacitor that was copied is at the bottom of the picture and the three waxies at the bottom end have also been re-stuffed. Note the burnt out resistor has been replaced with a new one and the damaged wiring re-sleeved.

Cheers
Andy
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Old 30th Aug 2019, 10:58 am   #86
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Default Re: Baird Garrick

Very nice!

Peter
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Old 30th Aug 2019, 11:39 am   #87
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Default Re: Baird Garrick

This is the way it's going with the restoration of early TVs and radios. We're do our very best to return the old electronics back to the original appearance. No more horrible Hi-Viz capacitors on show. The only worry of course is if a set was to fall into the hands of someone else who then takes a look at all the old looking components and decides to replace everything we painstakingly replicated. It would be a good idea to keep a service record with every set.

DFWB.
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Old 30th Aug 2019, 11:49 am   #88
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Default Re: Baird Garrick

I have seen masks successfully cut from large pieces of expanded polystyrene (easily obtainable) and the area of the mask that you see is then overlaid and shaped with plaster of paris by scraping and sanding etc. Alternatively - though far less easy - fashion from wood.
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Old 4th Sep 2019, 11:45 pm   #89
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Default Re: Baird Garrick

Hi all,
not long to go before power up
Here you can see a general view of the vision chassis. Note that the rogue flyback EHT line output transformer has been put back for now.

The waxies on the tube base panel still need rebuilding, felt strips need to be added to the woodwork to cushion the tube, the aquadag earthing needs to be worked out and the new CRT fitted.

Of course a replacement set of valves has been fitted (they were nearly all missing), most of which were NOS. When I opened up the box containing the rare SP42, I found it was from the BBC valve department - I hope they don't want it back

Cheers
Andy
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Old 10th Sep 2019, 12:44 am   #90
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Hi all,
after re-stuffing the remaining caps on the CRT base board, I thought now might be a good time to power the set up before I fit the CRT.

I lugged the heavy PSU on to the bench and connected it up with the fuse to the mains EHT transformer disconnected.
In the second picture you can see the orange glow of the 100V reference for the focus regulator.
At first there was no line whistle, although there was a very loud noise coming from the frame coils. I swapped the Mazda PEN46 that I had fitted in the frame generator position with the VT127 (PEN46 clone) which I had in the line stage and this time I got line whistle, but no frame noise.
I did wonder if the Rayethon VT127 (which was a NOS WW2 air ministry valve) was no good in a self oscillating output stage. I didn't have a spare Mazda PEN46, but fortunately I did have a spare NOS VT127. Lucklily this one worked ok.
The third photo shows the faulty valve - it looks ok and I was the first person to open the box since it was re-labled with a CV number.

I attached a scope to the feedback winding of the frame output circuit and it showed a nice waveform which had 50Hz nicely in the range of the hold control. Turning up the height seemed to cause a breakdown which turned out to be the spark gap in the x100 scope probe Notice the size of the flyback pulse on the scope . Removing the probe enabled me to turn the height control right up. The scope probe survived intact . I wonder how high the anode voltage goes during the frame flyback?

I attached the scope probe across the line coils and got a lovely waveform. Again 10KHz was easily in range of the hold control. I then fed in the test card from an Aurora and was able to lock the timebases. The scope picture shows a nice 10.125KHz locked waveform

The HT was 365V.
The flyback EHT was rather low at 4.11KV. Maybe the EY51 is a little tired. However, when the set was first obtained it was noted that there had been a wax leak from the line output transformer. It turns out that the wax from the EHT rectifier's heater winding has gone gooey, so maybe there is an EHT leak there. I must look out an EHT stick and try it.

That's all for now.

Cheers
Andy
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Old 16th Sep 2019, 11:33 pm   #91
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Default Re: Baird Garrick

Hi all,
this is the first of a two part update.

I tried an EHT diode in place of the EY51, but still got no more than about 4kV. So I put the EY51 back in circuit.

I used a piece of 35mm waste pipe to ansue that the scan coils and CRT clamp were reasonably in line.

Next I attached some felt strips to the wooden CRT support, together with an aquadag earthing contact.

Next up - fitting the CRT...

Cheers
Andy
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Old 16th Sep 2019, 11:54 pm   #92
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Hi all,
part 2 of 2 of my update.

I installed a NOS CRT. It is an MW31-74 which has a cavity style anode connector and also requires an ion trap magnet. John (Heatercathodeshort) very kindly provided me with an ion trap magnet and a cavity to top cap anode adaptor (see second photo).

I powered up the set and after fiddling with the ion trap magnet, I got a picture of a sort...

The focus is poor due to the low EHT and the line linearity is terrible. I will have a go at trying different screen feed resitor valves for the line output valve when I get the chance; to see if that solves both problems.

Another issue is image cut off slightly on the left-hand side. This is mostly due to the ion trap magnet no quite being in the right place. The fourth picture shows the problem. The magnet ring is behind the focus coil, and it is just below the 10K resistor behind the paxolin panel. It really needs to be nearer the tube base, but if put the other side of the panel it interferes with the solder tags. I need to think about this one...

The last photo shows the CRT guarantee card. Do you think it is still valid?

Cheers
Andy
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Old 17th Sep 2019, 8:25 am   #93
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Default Re: Baird Garrick

Quote:
Originally Posted by beery View Post
Another issue is image cut off slightly on the left-hand side. This is mostly due to the ion trap magnet no quite being in the right place.
Cheers
Andy
Hi Andy,

I wonder if this might be another case of David's magnetised scan yoke and shifting the ion trap to compensate for it is cutting off the beam?

Peter
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Old 19th Jun 2021, 6:00 am   #94
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Default Re: Baird Garrick

Reopened by request
Cheers
Mike T
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Old 19th Jun 2021, 8:23 am   #95
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Hi everyone,
Mike has kindly reopened this thread because finally the end of this restoration is in sight.

After a long hiatus, the purchase of a suitable rubber mask was the push this project needed to get it going again.
More on this a bit later today I hope.

Cheers
Andy
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Old 19th Jun 2021, 1:17 pm   #96
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Here we go! First of all the story of the mask and another CRT

I recently found a 12" round CRT being advertised for sale online. What was unusual about it, was that it was mounted on a wooden frame, together with part of the front of an old TV and included the CRT mask as well.
I put in an offer and it was accepted. I offered more than an untested 12" CRT, because it was the mask I was really after and I didn't want to miss out on the sale.

A friend helped me collect it from a place near the Cambridge fens, between Cambridge and Peterborough. IT turned out to be amongst the last items being sold by a collector who had to give up his hobby for health reasons. He still kept his favourite sets and it was nice seeing the small collection he had left. Whilst there I was able to buy some vintag components as well.

When I got home I found that the CRT in question was a Mullard MW31-18. Being a straight gun tube, it is a much better replacement for the original MW31-7 in the Baird Garrick other than the MW31-74 that I had fitted. The ion trap magnet of the MW31-74 was really in the way of things. I tested the CRT and it was just into the good area, in fact I was sure it was better than this as the meter on my tester is a bit sticky.

The rubber mask is a much better replacement than the Bush TV24 style mask that I was planning to use. The extra picture width required to fill the 'double D' mask was going to be a problem, the cabinet had no way of mounting the mask and the outer edges of the mask were not wide enough to fill the safety glass.
The newly obtained mask was of the type that holds the safety glass as well. This arrangement ususally causes the mask to deform due to the weight of the glass and this mask was starting suffer in that way. As the Baird Garrick hs the safety glass fixed to the cabinet, I decided to cut off the part of the mask that retains the glass.

More to follow...

BTW, I never did find out what set the CRT came from. The scan coils look a bit PYE like, indeed the mask looks like a larger version of the LV30 mask, rather than a GEC one which has much thinner rubber. The scan coils had a four pin plug on a bit like a Vidor and the focus unit was an off the shelf item. The badge at the front was merely a transfer (now missing), I wondered it if was from a Sobel. Any ideas?

Cheers
Andy
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Old 19th Jun 2021, 8:49 pm   #97
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"BTW, I never did find out what set the CRT came from. The scan coils look a bit PYE like, indeed the mask looks like a larger version of the LV30 mask, rather than a GEC one which has much thinner rubber. The scan coils had a four pin plug on a bit like a Vidor and the focus unit was an off the shelf item. The badge at the front was merely a transfer (now missing), I wondered it if was from a Sobel. Any ideas?"
Hi Andy,
it might be from a Peto-Scott. There's a TV127 chassis and scan coils upstairs and the coils look similar to those on your CRT unit.

DFWB.
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Old 19th Jun 2021, 11:22 pm   #98
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Hi David,
I think you've found it!

Cheers
Andy
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Old 20th Jun 2021, 4:55 pm   #99
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Default Re: Baird Garrick

There appears to be very few adverts for Baird receivers especially the Garrick.
You may have seen this one Andy. W.W. November 1948. John.
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Old 21st Jun 2021, 12:25 am   #100
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Thanks for that John. I have got another copy of it somewhere.
The points listed in the advert are indeed its best points.
The push-pull video drive gives great contrast without flyback lines.
The focus is indeed current regulated.

There is no mention though of the poor picture linearity (no adjustments for that) or that the contrast control is buried deep within the set or of course one of the most lethal mains EHT arrangments that there ever was.

Anyway, back to the restoration.
Folks may remember that the original style line output transformer needed to be recreated. Early on in the restoration I swapped out the smoothing choke in the radio section for another one of a different shape. This gave me the lamminations and bobbin for the line output transformer (they are a very unusual size).
For the original transformer, a split bobbin was used. To achive this I made up a gerber file, using Altium, of the outline of one half of one of the end cheeks. I then used a CNC router to rout two identical end cheek halves. These were then glued to the bobbin with epoxy.

As for turns ratio, wire size and inductance, I knew none of these. I had planned to take some detailed measurements from the restored Lyric set, but Covid restrictions prevented this. So it was trial and error. After serveral iterations, I now have something that works. The primary is much fatter than the original and I could have another go at with thinner wire, but as it works I shall leave it as it is. This transformer is not wavewound. The split bobbing helps lower the capacitance, but also the over sized bobbin allows quite thick wire to be used for the primary which greatly helps to reduce capacitance by producing a fatter coil.
The primary is 1250 turns of 27 SWG and the secondary is 600 turns of 29 SWG. I think that 29 SWG for both windings would have been better.
Anyway, it works quite well. Line linearity is not perfect, but was better than with the tranformer that was in the set when I got it.

More to come...

Cheers
Andy
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Last edited by beery; 21st Jun 2021 at 12:28 am. Reason: forgot to upload pictures
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