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 > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 24th Feb 2019, 6:49 pm   #121
Andrew2
Nonode
 
Andrew2's Avatar
 
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,034
Default Re: Types of CRT used in colour TV's.

Heat around a hot component will slowly 'cook' the PCB until it begins to turn dark brown, then black. If this was all that happened it wouldn't be so bad, but it would often become conductive, causing circuit malfunction. I recall the (in)famous Pye CT205 suffered from this on the video output board, which would slowly turn to toast. The PCB could be replaced, but this would be expensive, so often a hole was drilled and then a small file could be used to remove the conductive area. Any copper tracks could be replaced with tinned copper wire. That's how we did it anyway.
High voltages, particularly high pulse voltages could also cause the board to turn conductive. With high voltages present, 'tracking' could occur across the affected area, which would quickly make matters even worse. Again, removal of the affected part of the PCB was the cure.
__________________
Andy G1HBE.
Andrew2 is offline  
Old 25th Feb 2019, 10:10 am   #122
ricard
Octode
 
ricard's Avatar
 
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,631
Default Re: Types of CRT used in colour TV's.

Slightly off topic, but it struck me after perusing this thread that picture tubes are called precisely that in both the US and Britain, whereas things like ECC83 and PL509 would be called 'tube' in north America and 'valve' in Britain. Is there any explanation for this?
ricard is offline  
Old 25th Feb 2019, 2:21 pm   #123
Hybrid tellies
Nonode
 
Hybrid tellies's Avatar
 
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
Default Re: Types of CRT used in colour TV's.

I have just enjoyed reading through all seven pages of this interesting topic. When I started in the trade, 1976, most colour TV's that we had out on rental used the 90 degree delta gun tube. It always amazed me that all these different makes all used the same type of CRT's but the picture quality varied greatly. The very best pictures were produced by the ITT CVC 5-9, Decca Bradfords and the Philips G8, the worst pictures being the Pye 691-697 and the BRC 8500'S. Of all the colour sets of this era it was fascinating that we never needed to replace a tube on any of the ITT CVC 5-9's despite the fact they used the same make of A56-120X or aA-120X tubes as all the other makes.
As these sets were starting to age tube replacements became a regular event, apart from the ITT's, and provided a decent regun tube was used, either Mullard or Mazda, good as new results could be achieved by careful setting up of the convergences, greyscale, preset brightness, and beam limiting. For us replaceing and setting up delta gun tubes became second nature.

As for Thorn fitting there tubes upside down we were told that Thorn thought that this improved the quality of the picture for the typical viewing angle used by most customers in their living rooms. The small screen Decca Bradfords also fitted their tubes upside down probably for the same reason but there large screen sets fitted the tubes normally?!.

The only 110 degree delta gun tubes that we saw were in the Philips G9 chassis. They generally gave good pictures but were slightly more difficult to converge especially around the corners and they could also suffer a kind of dark shadow patching apparently caused by the localised heating of the shadow mask on bright scenes.

The first inline tubes that we came across was the RCA in line tube used on the Thorn 9000 and ITT CVC 20. The pictures certainly looked brighter but looked slightly blurry when compared to a 19/20" delta gun tube. I remember the first sets fitted with the Mullard 20AX tube they gave better pictures than the RCA Inline tubes with a slightly sharper picture with the best 20AX pictures from those that were fitted to the Decca 100 chassis.

Over the years these in line tubes became more refined and efficient giving brighter pictures for less power but it took them a long time to match the pin sharp definition that could be achieved by a good well set up 90 degree delta gun tube.
__________________
Simon
BVWS member

Last edited by Hybrid tellies; 25th Feb 2019 at 2:35 pm.
Hybrid tellies is offline  
Old 25th Feb 2019, 6:15 pm   #124
slidertogrid
Octode
 
slidertogrid's Avatar
 
Join Date: Apr 2005
Location: Peterborough, Cambridgeshire, UK.
Posts: 1,897
Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Hybrid tellies View Post
It always amazed me that all these different makes all used the same type of CRT's but the picture quality varied greatly. The very best pictures were produced by the ITT CVC 5-9, Decca Bradfords and the Philips G8, the worst pictures being the Pye 691-697 and the BRC 8500'S.
Not all CVC series sets were fitted with Mullard tubes some were fitted with Toshiba Tubes. The same applied to the GEC sets both the hybrid and the first solid state sets. the Tosh tubes gave a good picture when new but often lost emission after a couple of years , any attempt to boost the tube resulted in success for about an hour!
I don't agree that the 8500 gave inferior pictures if correctly set up they were just as good as any other delta gun sets.
The award for crappiest picture on a delta gun set must surely go to the CT200 mark 1 with the low focus tube and picture size control labelled 'brightness'
Followed by The Bush Murphy 823 two chip decoder sets especially the varicap ones! Purple reds and ropey AFC.. Set it all up and it was fine for a week...
Not forgetting the simple pal Teletons. PAL on those stood for Purple Alternate Lines...


Rich

Last edited by slidertogrid; 25th Feb 2019 at 6:20 pm.
slidertogrid is offline  
Old 25th Feb 2019, 10:00 pm   #125
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Hybrid tellies View Post
Over the years these in line tubes became more refined and efficient giving brighter pictures for less power but it took them a long time to match the pin sharp definition that could be achieved by a good well set up 90 degree delta gun tube.
Funny, I just wrote this in another topic about Trinitron tubes (what's the smallest widescreen CRT in normal TV sets: probably a 16" Trinitron) that I think every new generation struggled a bit to get better results than inline tubes of the same era, maybe leapfrogging a bit (but in the end losing out because of the physical limitations I mentioned before).

Also inline struggeling to achieve the definition of a delta tube could partially have something to do with what I mentioned earlier about monitor tubes: a well thought out dot pattern can give a better resolution than just a striped pattern as standard inline tubes and Trinitron tubes, even in combination with an inline gun.

Another important factor in 110 degrees inline tubes not easily achieving the same geometry and convergence results as a 90 degrees delta tube, is the deflection angle. The wider the angle, the more energy and corrections needed to deflect the image just right. A 70 degrees roundie will give excellent results with relatively little effor, see the Philips K4 set at marcelstvmuseum.com

Also the screen curvature. The less curved, the harder to correct both focus and convergence/geometry. 32" widescreen tubes, and smaller computer monitor tubes, often used dynamic focussing. The focus tension was modulated with the horizontal deflection.

Last edited by Maarten; 25th Feb 2019 at 10:21 pm.
Maarten is offline  
Old 26th Feb 2019, 8:06 pm   #126
Philips210
Nonode
 
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Hybrid tellies View Post
The very best pictures were produced by the ITT CVC 5-9, Decca Bradfords and the Philips G8, the worst pictures being the Pye 691-697 and the BRC 8500'S.
Hi

I agree the ITT CVC 5-9 gave good results especially the 20" version but I found the Pye hybrids were capable of displaying a good picture. They were mainly let down by having poor EHT regulation and that CDA panel with its problems. The Pye did have a decent Mullard design decoder.
I never rated the RBM A823, it had by far the worst PAL decoder and often displayed horrible colour. I found they could be set up reasonably well but often drifted out of alignment. The A823 had a problem with its ITT chroma delay line going out of tolerance so it was difficult to set up the decoder without Hanover blinds.
Whilst I liked the Decca 10/30 series 'Bradfords' I sometimes found the decoder often displayed blinds as well. I can't recall if the Bradford used the ITT chroma delay line as with the A823.
I thought the G8 and GEC 2110 series gave excellent pictures. Both the G8 and 2110 series being great for servicing and would say the 2110 was better than the G8 for repairs and was reasonably reliable for a 1970s chassis.

Regards
Symon.
Philips210 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:33 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.