Can anyone identify this CRT

[space_charged]

OK, great. So it might be used to get a pre-war TV going. Might see if I can find a suitable set then.

[thermionic]

Originally Posted by Heatercathodeshort

I think the CRM92 is immediately after WW2. John.

Thanks for clarifying that, John. I had in my head that Murphy used a CRM92 in a (just) pre war set. I can't remember why I thought that!!!

What difference does the 'A' version have against the original?



Cheers. SimonT.

[Heatercathodeshort]

The original CRM92 was rated at a maximum EHT of 6kv. The A version had the neck manufactured to a higher insulation specification and has a maximum EHT of 7.5kv. The CRM92 can be fitted in place of the 92A but the neck must be wrapped in a single layer of polythene covering the scan coils and focus assembly.
In practice I doubt if any harm would have taken place if the insulation had been omitted.
Just to clear up the suffixes. CRM152A = 15" 'wide angle' White face screen requiring an optional external daylight filter if operated under bright light conditions.
CRM152B = Same tube but with darker tinted glass faceplate not requiring the filter. J.

[space_charged]

Thanks for the information about the difference between the CRM 92 and CRM92A. It would be OK for me to use my CRM92A then in a set designed for a CRM92?

I've just tested two of my MW36-24s. I'm looking to restore a Ferguson 992T. It looks like both tubes have some life, I get a good bright (defocussed) spot from both these tubes with 5KV EHT. One of my MW36-24s has been re-gunned and has a "ClearView" label on it rather than the original Mullard.

The other set is a Petto Scott but that is in poorer condition than the Ferguson. The wiring has deteriorated and a lot of it will have to be replaced. When I touch wires they tend to drop off!

Charles

[space_charged]

I don't know if anybody else does this, but I am considering running my CRTs heaters in my restored sets from a 6V mains transformer. I'm worried at leaving its heaters to the tender mercies of a series heather chain. It would avoid the switch on surge and also remove any heater/cathode voltage that might induce shorts. The CRT would be protected in case of anything nasty happening to the rest of the heater chain. OK I know the CRT is usually placed at the neutral end of the chain, but maybe better safe than sorry? I'm not thinking of overrunning its heater, just applying 6.3V ac.

I know there is a strong argument for keeping a set as original as possible, but such a transformer could probably be hidden under the chassis, so not obvious.

I'd welcome comments.

Charles

[Heatercathodeshort]

It is difficult to get any definite information but as you say Simon the CRM92 may have been used in the 1939 series Murphy V86C series. These models were made for the 1940 season and displayed at the 1939 Radioympia. These were never distributed until 1946 having been stored at a warehouse in Holborn London for the duration. Very rare receivers. John.

[Catkins]

Originally Posted by Heatercathodeshort

It is difficult to get any definite information but as you say Simon the CRM92 may have been used in the 1939 series Murphy V86C series. These models were made for the 1940 season and displayed at the 1939 Radioympia. These were never distributed until 1946 having been stored at a warehouse in Holborn London for the duration. Very rare receivers. John.

The Mazda authored booklet "Electrons in Picture Tubes" reproduced here http://www.r-type.org/articles/art-004e.htm#026 under the section "Development" (at the end of the article) gives some dates for the introduction of various Mazda CRT's and it gives 1939 for the CRM92

Triode Guns with Magnetic Focus. Non Aluminised.

9MH 9 inch diameter screen. Deflection angle 45° 1936
12MH 12 inch diameter screen. Deflection angle 45° 1937
CRM121 12 inch diameter screen. Deflection angle 50° 1938
CRM92 9 inch diameter screen. Deflection angle 50° 1939

The CRM92 seems to have been used in the Murphy V84T (again displayed at the 1939 Radioympia for the 1940 season) of which according to http://www.earlytelevision.org/murphy.html one survives.

This is probably the V84 which appears on the Radio Museum site http://www.radiomuseum.org/r/murphy_v84.html. This is listed as having a CRM92.

[Catkins]

Originally Posted by space_charged

OK, great. So it might be used to get a pre-war TV going. Might see if I can find a suitable set then.

As mentioned by others and myself in this thread, the 1939 Murphy 9" models probably used the CRM92 (at least the V84T), but as only one set seems to have survived finding one of these is unlikely

However there is an alternative, and that is the previous Murphy models introduced in 1938, the television only A56V, and the television/radio A58V, these used the earlier CRM91, but as that is rarer then hens teeth in working condition, they can be modified to use the CRM92. According to the pre-war television database http://www.earlytelevision.org/database_prewar.html there are 8 and 7 of these respectively known to survive, and more could come to light.

I have one of those A56Vs, and it has a broken CRM91, and so I have no choice but to fit a CRM92. I wrote up a thread last year where I restored a Baird Portable from 1949 which uses a CRM92, to use as a test-bed for checking the CRM92's I manage to find. That thread http://www.vintage-radio.net/forum/s...d.php?t=126426 may be of interest.

As regards my A56V, that came to me in very poor condition, as can be seen from the attached photos 1 and 2.

I have spent the last one and half years restoring it, which due to its condition has been a slow and painstaking task. I am finally reaching the end of the tunnel as can be hopefully been seen in the other photos. The third photo is from a couple of months ago when I had sound output working. The last photo is from a couple of days ago when I have restored and put back most of the time-base circuits (the extra bits on the chassis). I still have to make an adapted mount for the CRM92 tube, and put back that and the focus/deflection coils.

[brianc]

The progress that you have made is fantastic! It is so convenient that the valve bases fit underneath the chassis where most of the wiring is so that it is possible to drill out/remove the bases complete with the wiring so that the chassis may be completely re-finished as per original and the re-furbished wiring replaced as it was when it was first made. Therefore this does not detract from the originality of the set and the work done to it.
How were the set's wound components? These are the ones which normally suffer from damp during storage when the dreaded green spot becomes active and all the wound components are affected. Particularly difficult when tuned circuits are affected, especially Litz wire.
I'm looking forward to seeing a picture on the screen and the cabinet and mask refinished. Good luck with the processes involved.

[Catkins]

Originally Posted by brianc

How were the set's wound components? These are the ones which normally suffer from damp during storage when the dreaded green spot becomes active and all the wound components are affected. Particularly difficult when tuned circuits are affected, especially Litz wire..

The general condition of all the metal work, extremely rusty, is what has taken the time to restore properly. With regards to the wound components, the transformers were basically lumps of rust, but strangely enough the windings tested OK, which given the state of the metal work was very surprising. This situation is obviously good and bad. With shorted or O/C windings you at least know where you stand, but with windings which test good it is essentially a "suck and see it approach" when you put load on them. In the meantime I did what I can, treat the rust and bake the transformers. Then fingers crossed when you power it up

The aerial coils/IF coils also tested OK, and a visual examination showed all were surprisingly free of corrosion. The oscillator coil on visual examination showed some green spot (where it was close to the case, obviously a moisture trap), but it luckily tested OK on the meter. I have carefully treated the corrosion and lacquered the coil, and it should hopefully be OK.

This is obviously why powering the set up "early", when I had got the circuits restored to the extent that sound output should work was important to me. It would be an important test of the mains/audio transformers and the various coils in the tuned circuits. Happily bar one quickly rectified fault, everything worked OK.

I have attached a couple of pictures which may be of interest. Photo 1 is a photograph of the frame transformer, which you should be able to see is extremely rusty, rust pockmarked with deeper spots of blacker corrosion. The rust had penetrated deeply, photo 2 is a photo of the condition of the laminates, with the worst and best conditioned laminate. Photo 3 is the transformer bracket with most of the corrosion removed. It is still not very healthy looking, and the layer was still rather soft and brittle. However as the corrosion had removed so much of the surface, it was impossible to remove any more of the diseased metal without destroying the integrity. At this point I investigated various ways of "building it back up" to a reasonable finish and drew a blank. Electro-plating seemed the best method, but at this point you will quickly discover electro-plating is one of those "garbage in, garbage out" methods, the surface has to be good to begin with otherwise the plate will be rubbish. The typical solution here with electro-plating is grind the surface down to good metal, but of course I was unwilling and couldn't do that anyway.

I finally discovered there is a way of re-building the surface using electro-plating, but it is not often used because it is expensive and time consuming. Basically you repeatedly plate with "thick" coats of copper plate, which because it is soft, can be slowly polished down between each plate, until a good unblemished surface is obtained. The snag is it takes lots of plates, the additional snag is you cannot electro-plate copper to steel, and so you have to first plate with nickel, and then, obviously, do a final plate of nickel on top of the copper.

I can't give a photo of the metal work plated with copper because I'm out of attachments, but photo 4 is the final result. 2xnickel plates, 5xcopper plates and a zinc plate tool to make the final result closer to the original chromium finish.

Photo 4 is the oscillator coil showing the treated and lacquered coil. I should have taken a photo prior to the work but I obviously forgot.

Originally Posted by brianc

I'm looking forward to seeing a picture on the screen and the cabinet and mask refinished. Good luck with the processes involved.

I should hopefully finish the electrical work later this year.

I have not touched the cabinet yet. Cabinet work is something I have never done, but I'm willing to learn here. Alternatively I'm open to suggestions as to how I can get the cabinet restored.

[FERNSEH]

Quote Catkins "However there is an alternative, and that is the previous Murphy models introduced in 1938, the television only A56V, and the television/radio A58V, these used the earlier CRM91, but as that is rarer then hens teeth in working condition, they can be modified to use the CRM92. According to the pre-war television database http://www.earlytelevision.org/database_prewar.html there are 8 and 7 of these respectively known to survive, and more could come to light."

The CRM91 failed in my Murphy A58V and as a replacement the Mazda CRM92 was employed. Special spacer brackets were made for the slightly longer tube. (1") The CRM92 was subsequently replaced with the correct CRM91. I still have the spacer brackets.

DFWB.