UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 22nd Jun 2011, 8:10 pm   #21
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Rebuilt MW22-7 Tube in Bush TV1

I am certain that RACS will sort out the problem. This is not a criticism made to anyone in particular. If you do have a problem with any repaired tube you must in the first instance make contact with RACS, it is unfair to level any comment prior to them having had the chance to sort out the problem or make suggestions. In the case of Chipps set the problem may indeed be due to low EHT and that of course is not the fault of RACS as the CRT is running outwith its design parameters.
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 22nd Jun 2011, 10:05 pm   #22
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

I agree with steve .R A C S do a great service . This experiment is interesting , but I wish it wasn't my tube ;o)
chipp1968 is offline  
Old 22nd Jun 2011, 11:19 pm   #23
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Matthewhouse in Exeter has just told me he has a EHT meter probe on its way to him. so hope we can test it soon !
chipp1968 is offline  
Old 28th Jun 2011, 8:16 am   #24
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

I have had an answer from R A C S Apparently the glass has been damaged by long term use , by bombardment !
They will try to re do the tube with no charge ,and or use acid to try to remove any glass defect .But as the tube is incredibly thin glass I do not thing that would be the best thing to do, and so I will leave as is .
I will let Jerome explain the facts
chipp1968 is offline  
Old 29th Jun 2011, 3:06 pm   #25
jhalphen
Hexode
 
Join Date: Jul 2004
Location: Paris, France
Posts: 346
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Good Day Gentlemen,

Hi Paul,

Here is a rewritten for NG posting of the info obtained from RACS last friday (june 24th) and which i sent privately to Paul - Chipp1968.

I had a long talk friday june 24th about the CRT rebuild with François RAEDERSDORFF
the Head of Rebuild Engineering operations.

For those who like speed-reading and quick to-the-point conclusions, in a nutshell: the glass at the centre of the screen has been damaged beyond repair by eons of ion and electron bombardment.

The long version:

CRTs without aluminized screen are under constant ion bombardment, also receivers without fast spot extinction circuitry upon turnoff - i.e. where a bright stationary point of light remains in the centre of the CRT which slowly fades away actually damage the glass's intimate crystalline structure through probably decades of use and several thousand on/off switchings. the glass become harder, darkens and looses transparency.

How can one affirm such a statement? well, once the to-be-rebuilt tube is brought back to a transparent glass vessel condition i.e. after total washing off of the phosphor and graphite coatings, one can see a browned glass defect area at the centre of the tube. The defect is non-repairable as the crystalline/molecular structure of the glass itself is modified.
Ever seen a well-used X-Ray tube? - The envelope looks like it's been dipped/stained in strong coffee.

Depositing a new P4 screen phosphor which RACS always does on any B&W CRT rebuild therefore changes nothing because the emitted light has to go through the altered/darkened glass area.

The "bombarded damage effect" even happens occasionally on new CRTs. François is due to send me a photo of such an example.

I asked François what would happen if the CRT was re-processed, this time using a higher concentration of hydrofluoric acid to "eat/leach away" at the thickness of the darker area on the inner surface of the screen? the answer was: "i do not recommend this, it has been tried and the affected zone increases in area and can become milky, so you then cumulate two defects: the darkened zone + worsened glass transparency creating a diffused light - out of focus effect, slap-bang in the centre of the picture tube."

He also commented that the type of glass used in the MW22-7 was new for the era and very thin in comparison with was then standard practice. RACS could rework the tube, but additional etching could weaken the sturdiness of the envelope and create liabilities in terms of structural integrity i.e. blowing-up during vacuum pumping or create a general increased susceptibity of failure under mechanical shock even if it was re-vacuumed successfully.

Actually, talking for nearly 45min with him, François was quite proud of the results achieved and seeing paul's photos displaying video he commented that the CRT was bright, well focused and with good geometry.

The initial question "perhaps not enough EHT" scenario was a false lead - Sorry!

To conclude, i will quote Panrock:
"It must be a very difficult and precise process to successfully refurbish vintage tubes on an individual basis. It's incredible that RACS has achieved the level of performance they have in doing this. Most of their tubes are fine, and occasionally when there's a problem they always do their best to put it right. Without them, where would we be?"

Thank you! Panrock. Much understanding and perception in your comment. Rebuilding CRTs will always remain a high-technology juggling act with a myriad of parameters where only previous experience gives guidance: dosing of chemicals, heating/cooling temperature graphs and durations, variable glass composition parameters (RACS routinely uses a spectrograph to analyze suspected non-standard glass composition compounds), rebuilding of guns, some 70 years old re-using original gun parts to make a new one with successful electron-optics characteristics mimicking the original's performance.

Brute force processes are also involved including very high temperatures, extremely flammable and/or poisonous chemicals, high KV electrics (up to 70KV) and violently explosive structural failures of vintage glass are ever-present dangers throughout the processing steps until the finished product is safely inside its shipping carton. All these possible pitfalls must be achieved with success for you to be pleased with the on-screen final result.
BTW, multiply by three if its a colour CRT...

All this having been said, Paul is a bit disappointed with his rebuild. A technical rework offering no real chance of improvement, i will see what can be done to ease the pain from a financial perspective. RACS has always prided itself on having satisfied customers so a mutually agreeable solution will be found.

In the meantime, the RAEDERSDORFF brothers have lost their 84 year-old father last saturday (and the founder of RACS) so this will wait until next week (funeral, etc.)

Best Regards to All,

jhalphen
Paris/France
jhalphen is offline  
Old 29th Jun 2011, 3:44 pm   #26
ThePillenwerfer
Octode
 
ThePillenwerfer's Avatar
 
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Fascinating stuff. I can well understand Paul's disappointment - I'm sure I'd feel just the same - but it seems that a miracle has already been achieved. Hopefully he'll stop noticing after a while.

Commiserations to the Raedersdorff brothers.

-Joe
ThePillenwerfer is offline  
Old 29th Jun 2011, 5:34 pm   #27
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Hello Jerome.
Please pass on my sincere condolences François and his brother on their sad loss.
Regarding the tube I suppose that there are many pitfalls in regunning and rescreening a CRT of its age.
One thing we forget is the integrity of the bulb will have changed over the years due to the natural cooling of the glass and of course the loading in the glass changes once the vacuum is released, only to be re-vacuumed yet again after the repair must also weaken the overall strength of these 60 + year old tubes.

I am sure now that Paul understands the trouble he will live with it. I for one must thank you for your clear and concise explanation.
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 29th Jun 2011, 11:24 pm   #28
Danny
Heptode
 
Danny's Avatar
 
Join Date: Jul 2003
Location: North Walsham, Norfolk, UK.
Posts: 516
Default Re: Rebuilt MW22-7 Tube in Bush TV1

This is quite interesting and informative so it looks as if Paul's tube will not get a big burn within months . I think this was his main worry. I tend to think of glass as a hard wearing material. But with an electron beam hitting it for years I guess any thing would weaken eventually. Danny
Danny is offline  
Old 30th Jun 2011, 8:21 am   #29
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Thank you Jerome for explaining that . The main disappointment for me was that I wasn't expecting this problem ,or aware that it could happen .It is a bit stressful sending the tube in the first place , then getting it back and making sure all is ok . As we know its also an expensive thing to get done .
I would certainly recommend having a tube rebuilt ,and will use R A C S again if I need to.
The work is professional and they send the tube back to you prior to payment which is very trusting !
Here are a couple of pictures off screen. My camera finds it difficult to take good ones unfortunately , I will try to take some more .
I think I need to adjust the coils as the picture is off centre. I think that we will still check the EHT voltage when possible too , just to make sure its running correctly.
Attached Thumbnails
Click image for larger version

Name:	DSC00025.jpg
Views:	275
Size:	41.8 KB
ID:	53214   Click image for larger version

Name:	DSC00012.jpg
Views:	309
Size:	59.9 KB
ID:	53215  
chipp1968 is offline  
Old 30th Jun 2011, 12:58 pm   #30
neon indicator
Retired Dormant Member
 
Join Date: Jun 2010
Location: Co. Limerick, Ireland.
Posts: 1,183
Default Re: Rebuilt MW22-7 Tube in Bush TV1

I remember people watching worse.

I suppose a tube rebuild is only likely if a replacement tube of similar vintage and identical type is unavailable.

OTOH... waxies are replaced by Met polys. Would it be terrible to get a 1930s or 1950s TV going with a 1960s or 1970s tube if absolutely nothing else was available and it looked "right"? Or is it criminal and only one step from fitting a Monochrome LCD!
neon indicator is offline  
Old 30th Jun 2011, 1:09 pm   #31
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,549
Default Re: Rebuilt MW22-7 Tube in Bush TV1

It's amazing that RACS can do anything with these old tubes anyway. Without dedicated people like them, many old sets would not be producing any pictures at all. There has to be a certain risk factor even to the point of the tube imploding during re-evacuation. Glass seals must be particularly difficult between old glass and new. Jerome and his team are doing a sterling job.

That's a good picture Chipp


SB
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is online now  
Old 30th Jun 2011, 11:06 pm   #32
jhalphen
Hexode
 
Join Date: Jul 2004
Location: Paris, France
Posts: 346
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Good day Gentlemen,

I have a scientific mind and like to get to the bottom of things.

Having the good fortune to be friends with a top-level Physics scientist working at the
National SuperConducting Laboratory, University of Michigan, USA:

http://www.nscl.msu.edu/

i queried him yesterday to get the scientist's answers about what actually damages glass irreversably over time. He is also a vintage TV collector and was interested in the topic.
He was kind enough to run some Physics software simulations and a real experiment.

I must format his replies for forum display, so i hope to do this tomorrow.

Sneak hint: and quite fascinating, most damage comes from long time electron bombardment and X-Ray emission, ions playing a minor role.

BTW, the NSCL owns the most powerful linear accelarator in the world in a civilian location.
Try to take time to browse the site, what they do there in terms of high energy Physics is really fascinating!

Best Regards

jhalphen
Paris/France
jhalphen is offline  
Old 1st Jul 2011, 7:51 am   #33
Andy Doz
Hexode
 
Andy Doz's Avatar
 
Join Date: Feb 2011
Location: Gloucestershire, UK.
Posts: 376
Default Re: Rebuilt MW22-7 Tube in Bush TV1

I spent a few years repairing linear accelerators and other medical bits and pieces, x-ray machines included. As commented earlier, a used x-ray tube is a coffee colour. Radiation has a horrible way of effecting materials. Zip ties used to go like glass and shatter.

Wasn't it a certain philips line transformer that used to turn a funny colour due to x-ray bombardment by the eht rec
Andy Doz is offline  
Old 1st Jul 2011, 8:47 am   #34
ppppenguin
Retired Dormant Member
 
ppppenguin's Avatar
 
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Look at the faceplate of an MW6/2 projection CRT http://www.r-type.org/exhib/aaa0291.htm These were run at 25kV and produced significant Xrays. The phosphor discoloured pretty quickly under the high loading but the glass also went brown.

I didn't realise that longer term bombardment with low energy electrons (<10kV potential, well below what's needed to make Xrays) could cause changes in the glass.
ppppenguin is offline  
Old 3rd Jul 2011, 11:11 pm   #35
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Some are some more off screen snaps. The camera has trouble focusing. Some taken in dark room and others with electric light on opposite the tv.
You can see its reflection in the cabinet . Some are DVD the last are live .Its perfectly watchable with room lighting on.
Attached Thumbnails
Click image for larger version

Name:	DSC00059.jpg
Views:	235
Size:	29.0 KB
ID:	53368   Click image for larger version

Name:	DSC00060.jpg
Views:	233
Size:	26.6 KB
ID:	53369   Click image for larger version

Name:	DSC00063.jpg
Views:	224
Size:	32.2 KB
ID:	53370   Click image for larger version

Name:	DSC00065.jpg
Views:	252
Size:	32.9 KB
ID:	53371   Click image for larger version

Name:	DSC00067.jpg
Views:	223
Size:	19.6 KB
ID:	53372  

chipp1968 is offline  
Old 3rd Jul 2011, 11:35 pm   #36
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,549
Default Re: Rebuilt MW22-7 Tube in Bush TV1

That's a great result. Picture looks really good.



SB
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is online now  
Old 4th Jul 2011, 7:50 am   #37
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Rebuilt MW22-7 Tube in Bush TV1

The results seem far better than on your first lot of pictures, have you done anything?
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 4th Jul 2011, 8:00 am   #38
chipp1968
Rest in Peace
 
chipp1968's Avatar
 
Join Date: Jul 2006
Location: Somerset, UK.
Posts: 2,356
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Yes it does seam better. I have not done anything yet. It may be that the camera has worked better .I took quite a few pictures ,and selected better ones .It does depend on what is being broadcast .Some things are very washed out and grey , yet others are more contrasty and vibrant , But I find that with all my sets.
Whether the tube has improved ,I don't know . I havant had any time to run it last week , so this was last night for an hour or two.
Strangely ,although its ok to watch in room lighting , the set doesn't like it when its sunny and im not talking about the sunlight actually across the set .Just very sunny outside .
Im getting used to the burn on the screen now ,especially now I know its not a rapidly growing thing!
chipp1968 is offline  
Old 5th Jul 2011, 8:38 pm   #39
FRANK.C
Heptode
 
FRANK.C's Avatar
 
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 732
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Hi Chipp those last pictures are looking good.
As Trevor has said above I have a little trouble with my rebuild. My tube produces a perfect static picture but if there is any movement there is a substantial afterglow. They asked for a video of it happening which until recently I wasn't able to produce in a format I could upload. I have just lately passed the links on to Jerome. The youtube videos are here and here. One is of a movie, the other is shining a lamp directly onto the screen After seeing them I think you would prefer to have your tube than mine.

I wish you a many happy years of enjoyment from your new tube.
Frank
FRANK.C is offline  
Old 5th Jul 2011, 8:51 pm   #40
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Rebuilt MW22-7 Tube in Bush TV1

Hi Frank
Has the effect got worse since you brought the set over to Scotland last year?
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:38 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.