Rebuilt MW22-7 Tube in Bush TV1 - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

neon indicator · 11th Jul 2011, 1:59 pm

Too high an EHT?

pichacker · 11th Jul 2011, 4:25 pm

Wouldn't the picture be too small in that case?

neon indicator · 11th Jul 2011, 5:17 pm

There is often a large variation of adjustment possible. Also beam current sets the deflection power needed. It's possible to have higher speed electrons due to excessive EHT, yet reasonable beam current due to bias of other anode(s), grid and Cathode. Though I'm not familar with tube. If brightness or A1 (if exists) has to be very low, suspect high EHT which can affect phosphor.

ppppenguin · 11th Jul 2011, 5:38 pm

Quote:

Originally Posted by neon indicator

Also beam current sets the deflection power needed.

I think you mean acceleration voltage. On a magnetically deflected CRT the deflection field required is proportional to the square root of the acceleration voltage. If it was proportional to current then light and dark parts of the picture would have different deflection sensitivity.

FRANK.C · 11th Jul 2011, 6:35 pm

Hi Chaps
Thanks for your comments.
I don't believe that the EHT is to high. This tube is rated to work at 10 kV and that is what I have measured it at. In fact at lower EHT the effect appears worse, but this is only because higher EHT gives a brighter picture which tends to mask the effect more.
The tube is a triode.

Frank

Heatercathodeshort · 11th Jul 2011, 7:06 pm

I don't believe for one minute that the EHT voltage has anything to do with the long persistence effects with your particular tube. The MW22-7 in it's original form is rated at a maximum of 7kv on it's final anode but as 98% of these tubes were operated from a mains derived EHT system it would rarely be more than 5.5kv. Add the aluminising and I would say that 7kv would be more than enough to give a bright picture on a 9" tube. The aluminised Mazda CRM93 in the TMB272 runs at 9kv maximum.
I don't know of any domestic 9" receiver that runs at 10kv. The Bush TV1 struggles at 5kv. All television tubes have to have a short to medium persistence phosphor and I think this one has a bit to much of the twinkle dust that produces the longer persistence. I don't think it's any more serious than that. Regards, John.

neon indicator · 11th Jul 2011, 7:13 pm

I don't really believe it either. A Straw clutching. But it's true that strange things can happen with too high EHT.

You're probably correct.

neon indicator · 11th Jul 2011, 7:16 pm

Quote:

Originally Posted by ppppenguin

Quote:

Originally Posted by neon indicator

Also beam current sets the deflection power needed.

I think you mean acceleration voltage. On a magnetically deflected CRT the deflection field required is proportional to the square root of the acceleration voltage. If it was proportional to current then light and dark parts of the picture would have different deflection sensitivity.

On reflection I was probably talking nonsense. Ignore. Infact the picture on some sets gets larger when Brighter due to poor EHT regulation, so of course you are correct.

FRANK.C · 11th Jul 2011, 7:27 pm

Sorry I didn't make it clear in my postings.
This is the Mullard MW31/74 tube that I got fitted with a Mazda CRM123 type gun.

Frank

Heatercathodeshort · 11th Jul 2011, 8:42 pm

Thanks Frank, that makes more sense. The MW31-74 is a brilliant tube with a true black and white picture. It would require 10kv when aluminised similar to the Brimar/Cintel C12B. J.

McMurdo · 11th Jul 2011, 9:04 pm

The dual-colour phosphor system, as we are guessing is at work here, was developed as an anti jamming measure in WW2. The blue short phosphor excites the yellow-green long phosphor and the blue image is then optically filtered out for the viewer. This causes locked images from aircraft returns to appear much brighter than unlocked or transient jamming noise.

source: Dick Barrett's The Radar Pages

FRANK.C · 15th Jul 2011, 6:35 pm

I received a phone call from Jerome today, we had a very enjoyable conversation about many things vintage, time just flew by and I am afraid I must have raised his phone bill considerably.

He explained to me that at the moment due to there recent bereavement the RAEDERSDORFF brothers were tied up, which is very understandable.

Jerome has found out that they do not mix the P4, they get it from a UK based firm. I was told the name of it but just cant remember it now.
He is hoping to have more information next week.
I will post updates as things develop

Frank

jhalphen · 15th Jul 2011, 6:51 pm

Good Day Gentlemen,

I had a long talk today with both Frank C. in Ireland and RACS, Southern France.

1) Frank's Long persistence P4 CRT video display pictures cannot be explained. The CRT was tested, and are all are post-rebuild CRTs, with X-Y raster and video content and all seemed OK.

RACS absolutely wants to have satisfied customers, so the sent to be rebuilt CRT will be rebuilt for the usual cost (+ shipping cost & insurance fees) if the customer wishes so.

Best Regards

jhalphen
Paris/France

geoff999 · 16th Jul 2011, 8:51 am

The title of this thread is now misleading as the current posts refer to a different tube and a different phenomenon.

The response from RACS as reported by jhalphen is rather disappointing as it does not help to explain the problem experienced by Frank C or make clear the terms of RACS offer of rectification.

murphyv310 · 16th Jul 2011, 9:15 am

Quote:

Originally Posted by jhalphen

RACS absolutely wants to have satisfied customers, so the sent to be rebuilt CRT will be rebuilt for the usual cost (+ shipping cost & insurance fees) if the customer wishes so.

Best Regards

jhalphen
Paris/France

Hi.
I know this is off topic now, but surely this problem should be repaired free of charge or at least at considerably reduced charge, The cost of repairing these CRT's is not cheap in the first instance, I saw this tube not long after it was returned to Frank and the problem was seen by a few forum members at the time.
I can understand that Frank will have to pay the carriage both ways, RACS though should make a better offer to be honest!

FRANK.C · 16th Jul 2011, 10:17 am

Hi Chaps
Yesterday while talking to Jerome the impression that I got was quite different from the one reflected in his post above. Maybe I misinterpreted what he was telling me I don't know. As far as I understood he had to talk to RACS again.

I'd be surprised if RACS didn't at least want to inspect the tube

Maybe Jerome can clarify things a little?

Frank

ppppenguin · 16th Jul 2011, 10:33 am

I wonder if something has been lost in translation here. While Jerome is totally bilingual French/English it's always possible that something has slipped.

chipp1968 · 16th Jul 2011, 11:04 am

Maybe he means at no cost except the post and insurance ?
My pre war tube is to go there soon , so Im hoping that will run smoothly !!!

murphyv310 · 16th Jul 2011, 12:39 pm

Yes I do hope so, perhaps it's a simple Typo or too many glasses of French wine

Heatercathodeshort · 16th Jul 2011, 1:09 pm

Yes it was rather a vague statement. I'm quite sure this will be sorted to everyone's satisfaction. J.

11th Jul 2011, 1:59 pm	#61
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Rebuilt MW22-7 Tube in Bush TV1 Too high an EHT?

11th Jul 2011, 4:25 pm	#62
pichacker Hexode Join Date: Aug 2008 Location: Essex, UK. Posts: 370	Re: Rebuilt MW22-7 Tube in Bush TV1 Wouldn't the picture be too small in that case? __________________ 6.3v on my heaters is no longer enough to get me going in the morning!!

11th Jul 2011, 5:17 pm	#63
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Rebuilt MW22-7 Tube in Bush TV1 There is often a large variation of adjustment possible. Also beam current sets the deflection power needed. It's possible to have higher speed electrons due to excessive EHT, yet reasonable beam current due to bias of other anode(s), grid and Cathode. Though I'm not familar with tube. If brightness or A1 (if exists) has to be very low, suspect high EHT which can affect phosphor.

11th Jul 2011, 6:35 pm	#65
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	Re: Rebuilt MW22-7 Tube in Bush TV1 Hi Chaps Thanks for your comments. I don't believe that the EHT is to high. This tube is rated to work at 10 kV and that is what I have measured it at. In fact at lower EHT the effect appears worse, but this is only because higher EHT gives a brighter picture which tends to mask the effect more. The tube is a triode. Frank

11th Jul 2011, 7:06 pm	#66
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Rebuilt MW22-7 Tube in Bush TV1 I don't believe for one minute that the EHT voltage has anything to do with the long persistence effects with your particular tube. The MW22-7 in it's original form is rated at a maximum of 7kv on it's final anode but as 98% of these tubes were operated from a mains derived EHT system it would rarely be more than 5.5kv. Add the aluminising and I would say that 7kv would be more than enough to give a bright picture on a 9" tube. The aluminised Mazda CRM93 in the TMB272 runs at 9kv maximum. I don't know of any domestic 9" receiver that runs at 10kv. The Bush TV1 struggles at 5kv. All television tubes have to have a short to medium persistence phosphor and I think this one has a bit to much of the twinkle dust that produces the longer persistence. I don't think it's any more serious than that. Regards, John.

11th Jul 2011, 7:13 pm	#67
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: Rebuilt MW22-7 Tube in Bush TV1 I don't really believe it either. A Straw clutching. But it's true that strange things can happen with too high EHT. You're probably correct.

11th Jul 2011, 7:27 pm	#69
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	Re: Rebuilt MW22-7 Tube in Bush TV1 Sorry I didn't make it clear in my postings. This is the Mullard MW31/74 tube that I got fitted with a Mazda CRM123 type gun. Frank

11th Jul 2011, 8:42 pm	#70
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Rebuilt MW22-7 Tube in Bush TV1 Thanks Frank, that makes more sense. The MW31-74 is a brilliant tube with a true black and white picture. It would require 10kv when aluminised similar to the Brimar/Cintel C12B. J.

11th Jul 2011, 9:04 pm	#71
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,277	Re: Rebuilt MW22-7 Tube in Bush TV1 The dual-colour phosphor system, as we are guessing is at work here, was developed as an anti jamming measure in WW2. The blue short phosphor excites the yellow-green long phosphor and the blue image is then optically filtered out for the viewer. This causes locked images from aircraft returns to appear much brighter than unlocked or transient jamming noise. source: Dick Barrett's The Radar Pages __________________ Kevin

15th Jul 2011, 6:35 pm	#72
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	Re: Rebuilt MW22-7 Tube in Bush TV1 I received a phone call from Jerome today, we had a very enjoyable conversation about many things vintage, time just flew by and I am afraid I must have raised his phone bill considerably. He explained to me that at the moment due to there recent bereavement the RAEDERSDORFF brothers were tied up, which is very understandable. Jerome has found out that they do not mix the P4, they get it from a UK based firm. I was told the name of it but just cant remember it now. He is hoping to have more information next week. I will post updates as things develop Frank

15th Jul 2011, 6:51 pm	#73
jhalphen Hexode Join Date: Jul 2004 Location: Paris, France Posts: 350	Re: Rebuilt MW22-7 Tube in Bush TV1 Good Day Gentlemen, I had a long talk today with both Frank C. in Ireland and RACS, Southern France. 1) Frank's Long persistence P4 CRT video display pictures cannot be explained. The CRT was tested, and are all are post-rebuild CRTs, with X-Y raster and video content and all seemed OK. RACS absolutely wants to have satisfied customers, so the sent to be rebuilt CRT will be rebuilt for the usual cost (+ shipping cost & insurance fees) if the customer wishes so. Best Regards jhalphen Paris/France Last edited by jhalphen; 15th Jul 2011 at 7:16 pm.

16th Jul 2011, 8:51 am	#74
geoff999 Rest in Peace Join Date: Jun 2007 Location: Croydon Posts: 92	Re: Rebuilt MW22-7 Tube in Bush TV1 The title of this thread is now misleading as the current posts refer to a different tube and a different phenomenon. The response from RACS as reported by jhalphen is rather disappointing as it does not help to explain the problem experienced by Frank C or make clear the terms of RACS offer of rectification.

16th Jul 2011, 10:17 am	#76
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	Re: Rebuilt MW22-7 Tube in Bush TV1 Hi Chaps Yesterday while talking to Jerome the impression that I got was quite different from the one reflected in his post above. Maybe I misinterpreted what he was telling me I don't know. As far as I understood he had to talk to RACS again. I'd be surprised if RACS didn't at least want to inspect the tube Maybe Jerome can clarify things a little? Frank

16th Jul 2011, 10:33 am	#77
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Rebuilt MW22-7 Tube in Bush TV1 I wonder if something has been lost in translation here. While Jerome is totally bilingual French/English it's always possible that something has slipped.

16th Jul 2011, 11:04 am	#78
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: Rebuilt MW22-7 Tube in Bush TV1 Maybe he means at no cost except the post and insurance ? My pre war tube is to go there soon , so Im hoping that will run smoothly !!!

16th Jul 2011, 12:39 pm	#79
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Rebuilt MW22-7 Tube in Bush TV1 Yes I do hope so, perhaps it's a simple Typo or too many glasses of French wine __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

16th Jul 2011, 1:09 pm	#80
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Rebuilt MW22-7 Tube in Bush TV1 Yes it was rather a vague statement. I'm quite sure this will be sorted to everyone's satisfaction. J.