Symptoms of a clapped out colour tube - Philips K40 - UK Vintage Radio Repair and Restoration Discussion Forum

harvestgold · 21st Jun 2007, 2:25 pm

I have an old Philips 22" TV dating from around 1984 ish (it is a super deluxe model with teletext!). The picture is OK, satisfactorily focused, but rather dull, even with the contrast and brightness on maximum. Is this symptomatic of a tube at the end of its life? I would love to get this set working in a decent manner rather than having to draw the curtains to watch it properly.

Thanks, Neil.

Welsh Anorak · 21st Jun 2007, 2:46 pm

Hi there
I'm afraid it does sound like the tube. Now is it a 20" or 22" set? Tube numbers - A51-570X is a 20", A56-540X is 22" and A66-540X is 26" for sets of that era. The chassis will probably be a KT3 or CTX-E for 20" - easy to spot as the KT3 folds down and the CTX has a flat PCB.
Bigger models used the K35 chassis - fold down. A less likely possibility is the KT4/K40 which fold down but use a plastic frame with a large PSU at the bottom. Tubes (generally badged Philips) seemed to last better in those.

Assuming a KT3 or K35, then there are things that can be done to improve emission. Assuming you don't have access to a reactivator (my first choice) carefully remove the CRT base (set off, usual precautions) and identify two small coils would on ferrite formers. Leaving them in position, short one out with a small lenth of wire on the print side. See how that improves the picture. This slightly increases the CRT heater volts. As the CRT is probably duff, you can aways short out the other one as well, but that does tend to over-run the heaters, so only if absolutely necessary.
Remember to remove the short(s) when you get a good CRT!

Good luck

Glyn

Welsh Anorak · 21st Jun 2007, 3:29 pm

Hi
It's generally accepted that these CRTs were under-run in the first place and removing some turns from one of the coils actually brings the voltage up to the correct 6.3v. Howver, I agree if you can get it to a decent reactivator it will last longer as long as it hasn't been done before.
BTW a customer I went to the other day (to tune in his new LCD portable, grrr) had a Philips K30 1002 (black front, non-remote) and a Panasonic NV2000 as his main sets - and the picture was superb! Can't say the same of the LCD....

Glyn

Studio263 · 21st Jun 2007, 3:54 pm

If the colour balance is reasonable and the picture does not de-focus when you max out the contrast and brightness I'd check the various resistors in the focus and A1 circuits first. Also check (prefereably by substitution) the capacitors that decouple the bottom end of the EHT winding (if present), failures here can confuse the beam limiter and give the symptoms you describe. Your set probably uses an A56-540X tube which should be capable of really good results.

Is it just as bad on teletext? If not a check around the PAL decoder is in order.

Welsh Anorak · 21st Jun 2007, 4:04 pm

Hi
These Philips sets do tend to wear out their CRTs this way. Sets such as the Amstrad 2200 (shudder) and Sanyo 22" didn't and were always handy donors for the nicer Philips sets. The only 'real' fault that might cause confusion is on a CTX when the decoupling capacitor on the EHT overwind fails, but then the contrast control won't work at all. Never had that on a KT3/K30.

Steve - I think the CVC sets had a Japanese tube, or at least an unusual make. Some KT3 20" sets had a Mitsubishi CRT fitted that went on for ever!

Glyn

Nickthedentist · 21st Jun 2007, 5:53 pm

Quote:

Originally Posted by harvestgold

It is a 22" tube, I think 110 degree as the cabinet is very shallow.

Undoubtedly an A56-540X as GD says. These give superb pictures but seem to be shortlived in the sets I've found them in (e.g. Philips K40, Decca/Tatung 130). The good news is that they seem to boost very well (or at least mine did)

harvestgold · 22nd Jun 2007, 7:26 pm

Sorry for the delay in replying, I had a surprise job on today (have to take anything I can get!). I'll be looking at the set tomorrow, hopefully.

I am pretty sure there was no flaring even with the brightness and contrast on full, just a rather dull picture.

Thank you. Neil.

harvestgold · 23rd Jun 2007, 10:42 am

I have just pulled it out and can quote the model number as being "22CS5744/05R", it definitely has the Mullard A56-540X tube.

The back plastic cover is date stamped as May 1984.

I can't find reference to this particular model number in my "Red Book" for 1983-84 so must be a slightly newer model, I guess.

The chassis is of the fold down type in a plastic frame with an additional board fixed to the bottom of the set.

A couple of photos are enclosed!

Neil.

Dave Moll · 23rd Jun 2007, 11:03 am

My index says it's in the next volume (1984-5), but the list of models in the volume itself doesn't include 22CS5744. After 2CS4860/05R (K40 chassis) it goes on to 26" models. There are 31 pages covering the K40 chassis!

Vectamart · 23rd Jun 2007, 3:15 pm

Hi, the photos show that the set is most definitely a K40 chassis. In my experience, the tubes in these generally lasted a good deal longer than the earlier versions of the 30AX tube fitted to the earlier K30 series.

When I was in the trade, we used to offer customers a four-year all-in guarantee and we caught a bit of a cold because so many K30s (and even more KT3s, KT4s and CTXs) were suffering from premature low emission CRTs. Generally, I found that it was usually possible to successfully re-activate a 30AX tube (as fitted to the K40 set refered to in this thread) and get a new lease of life measured in years rather than months.

Unfortunately, the Mullard labelled tubes used in the 20" KT3s, etc. were more often than not, actually made by Toshiba. The Mullard label was often stuck on the bowl of the CRT over the top of the Toshiba label. Funnily enough, Toshiba tubes (as well as some labelled Sylvania) were notorious for premature failure in the case of delta gun sets. I believe that I am correct in saying that Mullard never manufactured a 20" delta gun tube and always bought them in from elsewhwre and re-badged them. The givaway sign was that in the very small print on the label were the words "Made in Japan". These 20" delta gun CRTs turned up in 20" Philips G8s, GEC solid state chassis and quite a few others.

Interestingly, Toshiba tubes re-labelled Mullard also turned up in other sizes - for example, 18" Pye 713/5/7 chassis and Thorn 8000/8500 series. I have also had 22" versions fail prematurely - these often used to turn up, invariably with a yellow label, in the later versions of the Pye hybrid sets, e.g. CT205.

Getting back to the original thread, I agree that an attempt at reactivation, preferably usinng the supertior B&K instrument is probably the most likely method of improving the performance of the K40 in question, whilst minimising the risk of ****ing up the tube completely.

MALC SCOTT · 23rd Jun 2007, 4:08 pm

Philips use a choke in series with both sides of the crt heater on the K35 chassis. By shorting ONE of them out and running the set for a few hours always brought the emmision back to normal. This may be the same CRT heater set up used in the K40. The two chokes are located on the CRT base pcb. REMEMBER to REMOVE the s/c when you are finished Cheers, Malc.

harvestgold · 23rd Jun 2007, 5:57 pm

Right, I have been having a look around inside the set and staring at the circuit diagrams in the book, but I have to admit I am out of my depth here, rather than ploughing in and breaking it completely! Radios I can just about get my head round and I had good fun with my old KB black & white valve tv (before realising the LOPT was in all likelihood duff), but this is a bit beyond me.

I am tempted to have a go at Malc's suggestion and I have had a look for the capacitor that Danny Mentions but I am unsure exactly where I am looking and am having a crisis of confidence

Neil.

Welsh Anorak · 25th Jun 2007, 4:45 pm

Hi
If you don't have access to a rectivator, then try temporarily shorting out one of the coils - a faulty CRT will show an improvement, whereas if the fault is elsewhere there will be little difference, and as long as you only do it briefly no damage will be done to a good CRT.
Glyn

harvestgold · 25th Jun 2007, 7:21 pm

Well thank you everyone for your help, particularly Malc for pointing out exactly which components I was looking at! I replaced the offending capacitor and temporarily shorted out the choke to the heater as suggested and ran the set for a while. Now I have removed the shorting link and I have a greatly improved picture with much better brilliance - I only need the contrast and brightness controls advanced to normal levels rather than full on and it is viewable without having to draw the curtains!

Thanks again, Neil.

21st Jun 2007, 2:25 pm	#1
harvestgold Hexode Join Date: Jul 2005 Location: Worcestershire, UK. Posts: 282	Symptoms of a clapped out colour tube - Philips K40 I have an old Philips 22" TV dating from around 1984 ish (it is a super deluxe model with teletext!). The picture is OK, satisfactorily focused, but rather dull, even with the contrast and brightness on maximum. Is this symptomatic of a tube at the end of its life? I would love to get this set working in a decent manner rather than having to draw the curtains to watch it properly. Thanks, Neil.

21st Jun 2007, 2:46 pm	#2
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Symptoms of a clapped out Colour TV Tube Hi there I'm afraid it does sound like the tube. Now is it a 20" or 22" set? Tube numbers - A51-570X is a 20", A56-540X is 22" and A66-540X is 26" for sets of that era. The chassis will probably be a KT3 or CTX-E for 20" - easy to spot as the KT3 folds down and the CTX has a flat PCB. Bigger models used the K35 chassis - fold down. A less likely possibility is the KT4/K40 which fold down but use a plastic frame with a large PSU at the bottom. Tubes (generally badged Philips) seemed to last better in those. Assuming a KT3 or K35, then there are things that can be done to improve emission. Assuming you don't have access to a reactivator (my first choice) carefully remove the CRT base (set off, usual precautions) and identify two small coils would on ferrite formers. Leaving them in position, short one out with a small lenth of wire on the print side. See how that improves the picture. This slightly increases the CRT heater volts. As the CRT is probably duff, you can aways short out the other one as well, but that does tend to over-run the heaters, so only if absolutely necessary. Remember to remove the short(s) when you get a good CRT! Good luck Glyn

21st Jun 2007, 3:29 pm	#3
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Symptoms of a clapped out Colour TV Tube Hi It's generally accepted that these CRTs were under-run in the first place and removing some turns from one of the coils actually brings the voltage up to the correct 6.3v. Howver, I agree if you can get it to a decent reactivator it will last longer as long as it hasn't been done before. BTW a customer I went to the other day (to tune in his new LCD portable, grrr) had a Philips K30 1002 (black front, non-remote) and a Panasonic NV2000 as his main sets - and the picture was superb! Can't say the same of the LCD.... Glyn

21st Jun 2007, 3:54 pm	#4
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,577	Re: Symptoms of a clapped out Colour TV Tube If the colour balance is reasonable and the picture does not de-focus when you max out the contrast and brightness I'd check the various resistors in the focus and A1 circuits first. Also check (prefereably by substitution) the capacitors that decouple the bottom end of the EHT winding (if present), failures here can confuse the beam limiter and give the symptoms you describe. Your set probably uses an A56-540X tube which should be capable of really good results. Is it just as bad on teletext? If not a check around the PAL decoder is in order.

21st Jun 2007, 4:04 pm	#5
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Symptoms of a clapped out Colour TV Tube Hi These Philips sets do tend to wear out their CRTs this way. Sets such as the Amstrad 2200 (shudder) and Sanyo 22" didn't and were always handy donors for the nicer Philips sets. The only 'real' fault that might cause confusion is on a CTX when the decoupling capacitor on the EHT overwind fails, but then the contrast control won't work at all. Never had that on a KT3/K30. Steve - I think the CVC sets had a Japanese tube, or at least an unusual make. Some KT3 20" sets had a Mitsubishi CRT fitted that went on for ever! Glyn

22nd Jun 2007, 7:26 pm	#7
harvestgold Hexode Join Date: Jul 2005 Location: Worcestershire, UK. Posts: 282	Re: Symptoms of a clapped out Colour TV Tube Sorry for the delay in replying, I had a surprise job on today (have to take anything I can get!). I'll be looking at the set tomorrow, hopefully. I am pretty sure there was no flaring even with the brightness and contrast on full, just a rather dull picture. Thank you. Neil.

23rd Jun 2007, 10:42 am	#8
harvestgold Hexode Join Date: Jul 2005 Location: Worcestershire, UK. Posts: 282	Re: Symptoms of a clapped out Colour TV Tube I have just pulled it out and can quote the model number as being "22CS5744/05R", it definitely has the Mullard A56-540X tube. The back plastic cover is date stamped as May 1984. I can't find reference to this particular model number in my "Red Book" for 1983-84 so must be a slightly newer model, I guess. The chassis is of the fold down type in a plastic frame with an additional board fixed to the bottom of the set. A couple of photos are enclosed! Neil. Attached Thumbnails

23rd Jun 2007, 11:03 am	#9
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: Symptoms of a clapped out Colour TV Tube My index says it's in the next volume (1984-5), but the list of models in the volume itself doesn't include 22CS5744. After 2CS4860/05R (K40 chassis) it goes on to 26" models. There are 31 pages covering the K40 chassis! __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

23rd Jun 2007, 3:15 pm	#10
Vectamart Pentode Join Date: Feb 2007 Location: Ventnor, Isle of Wight, UK. Posts: 141	Re: Symptoms of a clapped out Colour TV Tube Hi, the photos show that the set is most definitely a K40 chassis. In my experience, the tubes in these generally lasted a good deal longer than the earlier versions of the 30AX tube fitted to the earlier K30 series. When I was in the trade, we used to offer customers a four-year all-in guarantee and we caught a bit of a cold because so many K30s (and even more KT3s, KT4s and CTXs) were suffering from premature low emission CRTs. Generally, I found that it was usually possible to successfully re-activate a 30AX tube (as fitted to the K40 set refered to in this thread) and get a new lease of life measured in years rather than months. Unfortunately, the Mullard labelled tubes used in the 20" KT3s, etc. were more often than not, actually made by Toshiba. The Mullard label was often stuck on the bowl of the CRT over the top of the Toshiba label. Funnily enough, Toshiba tubes (as well as some labelled Sylvania) were notorious for premature failure in the case of delta gun sets. I believe that I am correct in saying that Mullard never manufactured a 20" delta gun tube and always bought them in from elsewhwre and re-badged them. The givaway sign was that in the very small print on the label were the words "Made in Japan". These 20" delta gun CRTs turned up in 20" Philips G8s, GEC solid state chassis and quite a few others. Interestingly, Toshiba tubes re-labelled Mullard also turned up in other sizes - for example, 18" Pye 713/5/7 chassis and Thorn 8000/8500 series. I have also had 22" versions fail prematurely - these often used to turn up, invariably with a yellow label, in the later versions of the Pye hybrid sets, e.g. CT205. Getting back to the original thread, I agree that an attempt at reactivation, preferably usinng the supertior B&K instrument is probably the most likely method of improving the performance of the K40 in question, whilst minimising the risk of ****ing up the tube completely.

23rd Jun 2007, 4:08 pm	#11
MALC SCOTT Octode Join Date: Aug 2006 Location: Willington, County Durham, UK. Posts: 1,499	Re: Symptoms of a clapped out Colour TV Tube Philips use a choke in series with both sides of the crt heater on the K35 chassis. By shorting ONE of them out and running the set for a few hours always brought the emmision back to normal. This may be the same CRT heater set up used in the K40. The two chokes are located on the CRT base pcb. REMEMBER to REMOVE the s/c when you are finished Cheers, Malc. __________________ Malc Scott

23rd Jun 2007, 5:57 pm	#12
harvestgold Hexode Join Date: Jul 2005 Location: Worcestershire, UK. Posts: 282	Re: Symptoms of a clapped out Colour TV Tube Right, I have been having a look around inside the set and staring at the circuit diagrams in the book, but I have to admit I am out of my depth here, rather than ploughing in and breaking it completely! Radios I can just about get my head round and I had good fun with my old KB black & white valve tv (before realising the LOPT was in all likelihood duff), but this is a bit beyond me. I am tempted to have a go at Malc's suggestion and I have had a look for the capacitor that Danny Mentions but I am unsure exactly where I am looking and am having a crisis of confidence Neil.

25th Jun 2007, 4:45 pm	#13
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Symptoms of a clapped out Colour TV Tube Hi If you don't have access to a rectivator, then try temporarily shorting out one of the coils - a faulty CRT will show an improvement, whereas if the fault is elsewhere there will be little difference, and as long as you only do it briefly no damage will be done to a good CRT. Glyn

25th Jun 2007, 7:21 pm	#14
harvestgold Hexode Join Date: Jul 2005 Location: Worcestershire, UK. Posts: 282	Re: Symptoms of a clapped out Colour TV Tube Well thank you everyone for your help, particularly Malc for pointing out exactly which components I was looking at! I replaced the offending capacitor and temporarily shorted out the choke to the heater as suggested and ran the set for a while. Now I have removed the shorting link and I have a greatly improved picture with much better brilliance - I only need the contrast and brightness controls advanced to normal levels rather than full on and it is viewable without having to draw the curtains! Thanks again, Neil.