Ekco TC267/1 renaissance - or is it now?

[simonsradio]

Well, some time ago I raised a thread in which I said I had the carcas of the old family TV from the mid/late 50's which I had "modernised" as a teenager to receive BBC2. D'oh! The origional guts are long gone and I have been collecting bits for a few years to put it back as it should be. My earlier thread was about using a Ferranti T1001 chassis - I chickened out of that and restored the Ferranti....
Well today, it all came together and I thought the tale might be of some interest.
I used the chassis from a T293 which had been stored in a barn for decades. The cabinet was horrid but the insides basically sound.
The chassis came alive remarkably easily with a good drying out and lots of new caps. I think I found why the set was put aside - there was a short on the line blocking transformer connections where the sleeving on a component wire had punctured where it was dressed tightly round another tag on the transformer. The tube (CRM171) is a goodie. There were two problems - firstly the overwind on the LOPTX got really hot after ten minutes operation, and secondly one section of the TV/Radio switch had been wired out because the switch had burned. The LOPTX was changed for one from a scrap chassis acquired without cabint and incomplete (I will try to salvage the TX I removed - there cannot be much wrong with it and I was advised by the experts on this forum to dry it out in the airing cupboard.) I've been running the set for a week or two to test thoroughly and (how sad?) watched the Festivities last Friday on it. Time for major surgery to replace the TV/Radio switch with the one from the scrap chassis. Success - both TV and radio now working - and an improvement in picture quality now bringing up all bars on the test card. Hard to explain how/why since the wired-out section of the switch was heater wiring...
So this evening the transplant was undertaken and the T293 tube and chassis moved from the very sad old cabinet. Went smoothly except that the front controls didn't line up with the holes in the new cabinet . Many dodgy expletives before I stopped to look harder. Inspection showed that there were alternative mounting holes for the frame carrying the volume control, and for the mounting for the front of the tuner, designed to cater for different cabints, so this was all sorted out pretty easily by moving the mountings. The patinet came alive first try - for just 2 minutes then the line oscillator stopped. Although I had dressed the wiring on the line blocking TX, it must have been disturbed during the transplant and the same short had re-occured!
So here we are - one excellent set - and the best picture of my small collection. Its been on for the last couple of hours or more and completely stable. I'm really pleased with the outcome. There is just a couple of things I'd like advice on please. On dark backgrounds, the first inch or so of the left hand side of the picture is a bit lighter - not enough to show on a normal picture but definitely there on a dark background. And there is a bit of line pulling on peak white too. Any pointers welcome please!
Oh - and the original had Ekco spot wobble - this chassis doesn't. That may come as a future upgrade!
A few pics attached - the "interference" is down to my bad photography and not there in reality.
Now - what to do with the cabinet from the donor? To be completely stripped and refinished in due course, and then probably fitted with the "Television" B&W portable innards that were the means of the original "modernisation". Unless another CRM171 turns up - in which case I'll be tempted to try to rescue the scrap chassis too...

[simonsradio]

A couple of additional photos...

[Heatercathodeshort]

A nice transplant. The chassis are interchangeable in Ekco receivers due to a nice flow of standardisation that must have saved a fortune in tooling.
Regarding the shading. Check the flyback suppression capacitor .001uf to bottom end of frame blocking oscillator transformer to the tubes A1 supply. [Probably looks like a 1k resistor and coded the same!] If you are using an uncoated tube Mazda CRM171, the very slight shading can be caused by lack of EHT smoothing i.e. the Visconol disconnected. This can also cause slight line pulling on peak whites if the tube has very good emission due to line rate modulation of the beam at high beam currents.[brightness and contrast] Check also the CRT outer coating is earthed if this applies. [Mazda CRM172] Regards, John.

[murphyv310]

Excellent results and a very worthwhile transplant. The newer chassis will use the later 300ma valves which are easier to find.
I "Ekco" what John says about the EHT smoothing and the CRT's A1 supply.
Good Work

[simonsradio]

John, Trevor
Thanks. Yes, it is an uncoated CRM171 tube. It has an Ediswan label on it - might it be a replacement? It certainly produces a very crisp bright picture. The EHT smoothing is out of circuit so I expect that is the reason for the pulling and shading. I'll try to find a suitable capacitor to reconstruct the Visconol sometime - last time I looked they were pretty expensive though. I also seem to recall a thread in which it was suggested that it is possible to obtain the material to coat the bulb of the tube? I'll search it out later.

[oldticktock]

Hi Simon,

I have the 293 table version of your EKCO, I also bought some EHT caps a while ago to replace my duff Visconol, your welcome to one FOC

it's a .001 @ 15kV

Chris

[simonsradio]

Chris
You have a PM.
Regards
Simon.

[ppppenguin]

Originally Posted by simonsradio

....I also seem to recall a thread in which it was suggested that it is possible to obtain the material to coat the bulb of the tube?

Don't think this will work. You would need a conductive coating on the inside too, in order to make a capacitor. OTT has made a very kind offer and that's your best solution.

[oldticktock]

I'm surprised Jeffrey I thought that it had been done before with a TV22 using an EKCO TMB72 crt (CRM93) with conductive coating just to the outside applied.

[simonsradio]

An EHT cap it will be - thanks Chris . I will report on the difference i.d.c. ....

[Heatercathodeshort]

Originally Posted by ppppenguin

Don't think this will work. You would need a conductive coating on the inside too, in order to make a capacitor. OTT has made a very kind offer and that's your best solution.

Hello Jeffrey,
It is not often realized but all television CRT's have an internal conductive coating that is connected to the final anode. This is usually ended around an inch down the neck where it joins the flare of the bulb. In the case of the CRM171 the tube is also aluminised thus forming an excellent one half of the 'plate'. The only exception would be the small electrostatic types and the very early pre war tubes that had completely clear bulbs. I would agree that the addition of a capacitor is probably the best solution as attempting to get modern 'dag' to stick to glass appears to be impossible! Why Mazda left it so late to aluminise their 17" tubes is a mystery. Maybe their designer played golf with the owner of TCC.. Regards, John.

[ppppenguin]

Originally Posted by Heatercathodeshort

...
It is not often realized but all television CRT's have an internal conductive coating that is connected to the final anode.....

I bow to your greater experience. In mitigation I suppose I could say that I had visions of EMI 6/6 and similar tubes which don't have an internal conductive coating on the cone.

[Heatercathodeshort]

Spot on Jeffrey! Tubes tended to have in internal coating from around 1938 and this was connected to the final anode connector within the tube. Springs on the end of the gun assembly make contact with the final coating. A large gap exists between the final anode electrode and the focus/1st anode. If a tube goes down to air the insulation properties of the vacuum are destoyed and strong arcing can be seen within the gun.
Note arcing, not the classic blue glow from a gun where the vacuum is still reasonably good. J.

[simonsradio]

With thanks to OTT, an EHT cap is now fitted, and the metrosil back in circuit too. This has certainly improved EHT regulation and resolved the line pulling problem. The shading on the left side is reduced but still present, so when I have time, I'll go for the capacitor as suggested above...