Golborne Vintage Radio

I have an old pre-war picture tube /most likely Emiscope 6/6 12"/, which has a damaged anode socket. Corrosion was merciless to the metal electrode. I plan to gently clean the end of the electrode and connect it to a new short wire using electrically conductive glue. Before starting the procedure, I decided to check what the area around the anode socket looks like. For this purpose, I used two X-ray imaging methods, i.e. multi-row computed tomography and a regular X-ray. I suppose that no one has ever examined a picture tube using a tomography. I was waiting with great curiosity for the results of this modern examination. I started with it. Unfortunately, in this method, metal elements cause artifacts that significantly worsen the quality of the image. This is not surprising. People who have metal prostheses, e.g. hips, also have poor images, in this case the pelvis. Digital processing of CT images, on the other hand, allows for obtaining interesting three-dimensional images. What did CT finally provide? 
- The metal elements were blurred, I did not see any details 
- The glass near the anode socket has a longitudinal depression. The condition and length of the preserved metal fragment of the electrode are unknown 
- The thickness of the glass in the neck area is about 2 mm and is uniform 
- The thickness of the glass of the balloon is almost uniform and ranges from 4.46 mm to 5.08 mm 
- CRT balloon is made of two parts. The glass weld is very uniform, almost perfect throughout the entire circular course. It definitely protrudes into the CRT light 
- Tomography allows for tracing the layered structure of the glass of the entire CRT. I found only one air defect of 0.8x2 mm. I consider this an excellent production result 
- 3D reconstructions very realistically show the surface of the picture tube, the longitudinal depression in the area of the anode socket and the interior of the picture tube - you can take a tour of the interior of the picture tube 
To sum up, the CT scan very well illustrated the structure of the glass and the surface of the picture tube. I did not obtain any important information about the condition of the wire in the anode socket and the electron gun. 

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A radiologist friend suggested taking a regular X-ray. This method revealed much more practical information: 
- The structure of the glass around the surviving fragment of the anode electrode is correct and thick enough to perform mechanical cleaning 
- An electron gun, including the cathode and heater areas, look correct with preserved continuity of the microwires 
- Emiscope inscription clearly visible in X-rays must have a lead admixture in its structure.

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Now all that remains is to implement the CRT repair plan.

Adam.

Fascinating images. How did you get access to CT facilities?

That 6/6 looks like one of the later ones with a separate cone and faceplate. Earlier tubes were blown from one piece of glass. The presence of lead is interesting. All earlier 6/6 tubes were made from pyrex (borosilicate) glass which I don't think is compatible with lead. Most, if not all, later CRTs were made of soft (soda) glass which can have lead added. It's possible that some later 6/6 were soft glass.

Very interesting Adam!
Thank you.

Jac

I have a friend who is a radiologist. He was very interested in the old CRT. Without a moment's hesitation, he placed it in the tomograph tube. The device generated over 1K DICOM images. Layers every 0.5 mm. DICOM files can be processed in 3D graphics programs.

I think that the lead was only added to the paint used to create the Emiscope emblem. The manufacturer wanted this inscription to be durable.

What amazes me about the CRT is the perfection of its production. The balloon is very regular. The connection of the cover, i.e. the front of the CRT, with the cone does not raise any objections. We have to remember that we are moving in the 1930s. As I wrote, I found only one small air bubble in the glass structure.

The main problem with this particular CRT is the corrosion of the metal electrode of the anode socket. I think that this may be a problem with many CRTs from that era. Progressive erosion initially makes the electrical connection difficult and later may cause a loss of vacuum. I have another picture tube from TRK12 /RCA/, in which the metal anode has corroded almost completely. The result is now a lack of vacuum and a hole through the glass cone. From all this, perhaps a practical conclusion can be drawn that the anode sockets in all old picture tubes, especially pre-war ones, should be protected from further oxidation.

If 6/6 was produced in the early period as a single element, without connecting the front to the cone, it was a huge technological challenge. This type of picture tube probably has a more rounded, i.e. convex, front. The 6/6 picture tube that I am presenting with an attached glass front is flatter.

I think that the 6/6 with separate faceplate was post WW2. I'm not 100% sure of this. The early 6/6 had lots of air bubbles. Scary because each is a stress point. Back in 1986 when I shepherded a 6/6 through a rebuild we had a choice of tubes. We chose the one with fewest air bubbles as being least likely to implode during processing.

What a fascinating exercise and write-up.

You can compare the early and later 6/6 types here: https://www.nostalgiatech.co.uk/new_page_8.htm

Peter

(21-04-2025, 03:44 PM)peter scott Wrote: [ -> ]What a fascinating exercise and write-up.

You can compare the early and later 6/6 types here: https://www.nostalgiatech.co.uk/new_page_8.htm

Peter

Thanks for the link. It looks like my picture tube has an old type of electron gun. At the same time, the balloon is a later 2-part form. The tube for pumping the vacuum must be at the end of the neck. The 1-part picture tube was pumped from the cone level.

I am interested in:
- when did production of CRT 6/6 and similar end?
- were pre-war picture tubes replaced with more modern ones in old TVs as a form of modernization?

(21-04-2025, 10:08 AM)ppppenguin Wrote: [ -> ]I think that the 6/6 with separate faceplate was post WW2. I'm not 100% sure of this. The early 6/6 had lots of air bubbles. Scary because each is a stress point. Back in 1986 when I shepherded a 6/6 through a rebuild we had a choice of tubes. We chose the one with fewest air bubbles as being least likely to implode during processing.

Did you have new guns for the 6/6 rebuild? Was this work done as a service in previous years?

The existing gun was rebuilt with a new heater-cathode assembly. The HK assembly was available at the time as the same type was used in CRTs that were still available new (flying spot scanner CRTs). The gun rebuild was done by Thorn-EMI Electron Tubes who have long since disappeared.
https://www.borinsky.co.uk/vintage_tube.html

The HMV900 with this CRT is now owned by the Science Museum. I presume it's in their main store at Wroughton. It's not at Bradford. I visited there recently and saw their store rooms.

It was an interesting project of rebuilding an old CRT. Many people got involved in this work. Today it would be difficult to find so many enthusiasts. Was such a reconstruction later repeated? I suppose that the number of old working CRTs available today exceeds the number of preserved TV sets. So there is no need to consider rebuilding old CRTs today outside the scope of the experiment. Of course, I may be wrong. There is undoubtedly a demand for the color 15GP22. This would be a very complex project. In my country, there are still available CRTs from old Russian color TVs. They can be used as a donor. Of course, there is another problem with the 15GP22 related to its modular construction. 
Returning to the 6/6, what model of a more modern electron gun could be a substitute for the original version from the electrical point of view?

Adam