GEC Dual Standard Colour - UK Vintage Radio Repair and Restoration Discussion Forum

Niechcial,Steve · 13th Sep 2015, 4:37 pm

Hi all. I've just about finished restoring one of these and am left with a nagging fault someone may have experienced in those far off days of 1967 when beer could be had for two shillings (10P) a pint and what motorways there were were all nice and empty.
The fault is a 5mm white striation about 1.5 cm in from the left of the screen (on both standards). I suspect this set is prone to this problem. There is a mod. for it on the second production run (as fitted to my example). The service manual says that if that doesn't cure the fault then the LOPT is suspect. So it probably is the LOPT but if anyone thinks different I would be pleased to hear.
The set has come up surprisingly well, and I suspect has had relatively little use. The A63-11X is full of oomph on all three guns. There was a bottom creep frame fault which the previous owner had had a go at. I couldn't be bothered to fault find with those nasty Hunts caps around, and some replacement low power solid carbon resistors of 60s vintage in there as well, so I just rebuilt the whole stage. The high meg resistors in the Line Output stabilisation network had gone high producing low width. With full EHT restored, there was sizzling from the focus unit soon cured by a strip down and clean up, and that was about it for the main set. I just then had to take apart and thoroughly clean the VHF tuner. This is interesting because it's a Permeability Tuned type (i.e. the tuning selector moves cores up and down in inductors). I haven't seen this type of tuner other than in ancient car radios. Does anyone know of any other TV sets using this type?
I remember that these sets were a bit looked down on when they came out compared to other models. I think this was partly because they aimed for the bottom end of the price range, but perhaps also because they did away with the 25KV overwind, rectifier and shunt stabiliser. The pundits claimed the use of a tripler without the shunt stabiliser would mean poorer EHT regulation. In reality the EHT stabilisation is as good as any, and the build quality of the set better than many (e.g. generously rated pots.)

pbengtech · 13th Sep 2015, 5:36 pm

Hi,
It's a long time ago since working on these, but I seem to remember an o/c 1k5 ohm resistor could cause something similar to what you describe.. It may have been damping the line output transformer or the line linearity coil...
wiser heads hopefully will remember better than me.
Phil

HamishBoxer · 13th Sep 2015, 6:19 pm

Possibly that resistor would be across the Line Linearity coil.Common practice in most colour sets.

Niechcial,Steve · 13th Sep 2015, 10:13 pm

Yes thanks guys- your memory is very good. Sadly the 1K5 across the lin. coil checks out OK.

FERNSEH · 13th Sep 2015, 10:18 pm

Common fault on the GEC 2028. Velocity modulation effect caused by ringing in the linearity coil. It's L6 in the circuit diagram. The 1.5Kohm damping resistor R55 goes OC.

DFWB.

FERNSEH · 13th Sep 2015, 10:30 pm

There a resistor, R611 (1Kohm) which is connected across the line scanning coils. This resistor is located on the convergence board.

DFWB.

Peter.N. · 13th Sep 2015, 11:31 pm

If its a 2028 I had quite a few of these out on rent and I did experience that problem but can't for the life of me think what it was. I have vague recollections of it being something to do with the PL509 top cap. If you touch a few points in the circuit with a screwdriver it may change the position/pattern which might give you a clue.

Peter

Dr-Watts · 14th Sep 2015, 12:50 pm

I restored one of these a while back and mine did the same.
I never cured it either !
Dave W

micheal · 14th Sep 2015, 12:51 pm

Way back in 1970 i had the 0.1u/f decoupler on the screen grid of line o/p valve
PL509 go o/c but can't remember what fault it displayed, may be worth checking
Mike

HamishBoxer · 14th Sep 2015, 12:54 pm

Micheal,it was striations (possibly I spelt it wrong) common also on Thorn mono were it was an o/c 1uF.

Laurdys · 14th Sep 2015, 2:04 pm

Quote:

Originally Posted by Niechcial,Steve

It's a Permeability Tuned type (i.e. the tuning selector moves cores up and down in inductors). I haven't seen this type of tuner other than in ancient car radios. Does anyone know of any other TV sets using this type?

Yes, The bush T67 uses this tuning arrangement

ukcol · 14th Sep 2015, 2:28 pm

Referring to the symptom mentioned in post #1.

On the top cap of the line output valve, and also of the boost diode, there should be an anti Barkhausen oscillation choke. If one is missing or damage you can get a line down the screen, although I can't remember which side.

TonyDuell · 14th Sep 2015, 3:18 pm

I remember permeability tuners in Bush TVs going back to the 405 line monochrome era. The cores were plastic rods with little ferrite sleeves spaced along them which moved along long formers wound with several coils. It's been a long time since I've seen one, but I think there was a core/former for band 1, and another for band 3, with one of those flat sliding multi-pole switches to select between them. On top of the tuner were the normal PCC84 and PCF80 type valves

I remember one tuner that had the normal rotary selector with a cam arangement to operate the cores and switch. Another had 4 pushbuttons, 2 for band 1 the other 2 for band 3. Pressing a button operated the switch the right way and pressed on the end of the (spring-loaded) core to tune the thing.

Niechcial,Steve · 14th Sep 2015, 6:52 pm

Thanks guys for the fault info. and the tuner discussion. I will check out those possibilities and report back.

Niechcial,Steve · 14th Sep 2015, 8:04 pm

As Fernseh says, according to the manual R611 (1K) is on the convergence board. However in reality it is on the scan coils. It had gone up by 300R, and changing it has I think made things slightly better, but the striation is still there. The choke on the PY is fine. The circuit shows no choke fitted to the PL, but if someone can help me out with one from the scrap box, I'll try fitting it. I changed the screen grid de-coupler, but no joy there. I suppose I could also try a few ferrite beads around the place. I remember that sometime I the late 60s or 70s Practical television ran a whole article on BK oscillation.

Nuvistor · 14th Sep 2015, 8:27 pm

I think you must have leaned on the CR key, lots of blank space in the post, can you still edit it?

You should be able to make a coil for the top cap of the PL509, cannot remember exactly but half a dozen turns about 6 mm in diameter should do it. I seem to recall the boost diode top cap had them in some sets. Support the coil on a small piece of insulating material.
Frank
edit, missed the bit about the PY already having one, just make one like that for the PL

Hybrid tellies · 15th Sep 2015, 1:05 am

I had this problem a few times on the BRC1500 mono set, after changing the usual culprits I cleared the fault by replacing the 30FL2 line oscillated valve. So it might be worth changing the PCF802 line oscillated valve on your GEC colour set.

toshiba tony · 15th Sep 2015, 2:49 pm

Wasn't this called Barkenhausen Effect? I seem to remember sets that exhibited this could be fitted with a ferrite bead mounted as close to the anode of the line output bottle as you could. The early Decca hybrids suffered a lot (10 series) and I can remember curing a lot that way. Worth a try.

toshiba tony · 15th Sep 2015, 2:51 pm

Sorry, should have read all posts. Some other old timer beat me to it.

pichacker · 15th Sep 2015, 3:44 pm

I had a 2040 when I was a lot younger and mine had a similar effect that could be influenced by moving wiring around. Mine turned out to be an open circuit stabilising VDR (Or similar device) in the centre of the line board. One end had been lifted during a previous repair by someone. I know the 2028 is different but hey you never know if you have a similar failed component.

13th Sep 2015, 5:36 pm	#2
pbengtech Pentode Join Date: Jan 2009 Location: Birmingham, West Midlands, UK. Posts: 234	Re: GEC Dual Standard Colour Hi, It's a long time ago since working on these, but I seem to remember an o/c 1k5 ohm resistor could cause something similar to what you describe.. It may have been damping the line output transformer or the line linearity coil... wiser heads hopefully will remember better than me. Phil

13th Sep 2015, 6:19 pm	#3
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: GEC Dual Standard Colour Possibly that resistor would be across the Line Linearity coil.Common practice in most colour sets. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

13th Sep 2015, 10:13 pm	#4
Niechcial,Steve Hexode Join Date: Jan 2007 Location: Beckenham, London, UK. Posts: 373	Re: GEC Dual Standard Colour Yes thanks guys- your memory is very good. Sadly the 1K5 across the lin. coil checks out OK.

13th Sep 2015, 10:18 pm	#5
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: GEC Dual Standard Colour Common fault on the GEC 2028. Velocity modulation effect caused by ringing in the linearity coil. It's L6 in the circuit diagram. The 1.5Kohm damping resistor R55 goes OC. DFWB.

13th Sep 2015, 10:30 pm	#6
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: GEC Dual Standard Colour There a resistor, R611 (1Kohm) which is connected across the line scanning coils. This resistor is located on the convergence board. DFWB.

13th Sep 2015, 4:37 pm	#1
Niechcial,Steve Hexode Join Date: Jan 2007 Location: Beckenham, London, UK. Posts: 373	GEC Dual Standard Colour Hi all. I've just about finished restoring one of these and am left with a nagging fault someone may have experienced in those far off days of 1967 when beer could be had for two shillings (10P) a pint and what motorways there were were all nice and empty. The fault is a 5mm white striation about 1.5 cm in from the left of the screen (on both standards). I suspect this set is prone to this problem. There is a mod. for it on the second production run (as fitted to my example). The service manual says that if that doesn't cure the fault then the LOPT is suspect. So it probably is the LOPT but if anyone thinks different I would be pleased to hear. The set has come up surprisingly well, and I suspect has had relatively little use. The A63-11X is full of oomph on all three guns. There was a bottom creep frame fault which the previous owner had had a go at. I couldn't be bothered to fault find with those nasty Hunts caps around, and some replacement low power solid carbon resistors of 60s vintage in there as well, so I just rebuilt the whole stage. The high meg resistors in the Line Output stabilisation network had gone high producing low width. With full EHT restored, there was sizzling from the focus unit soon cured by a strip down and clean up, and that was about it for the main set. I just then had to take apart and thoroughly clean the VHF tuner. This is interesting because it's a Permeability Tuned type (i.e. the tuning selector moves cores up and down in inductors). I haven't seen this type of tuner other than in ancient car radios. Does anyone know of any other TV sets using this type? I remember that these sets were a bit looked down on when they came out compared to other models. I think this was partly because they aimed for the bottom end of the price range, but perhaps also because they did away with the 25KV overwind, rectifier and shunt stabiliser. The pundits claimed the use of a tripler without the shunt stabiliser would mean poorer EHT regulation. In reality the EHT stabilisation is as good as any, and the build quality of the set better than many (e.g. generously rated pots.)

13th Sep 2015, 11:31 pm	#7
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: GEC Dual Standard Colour If its a 2028 I had quite a few of these out on rent and I did experience that problem but can't for the life of me think what it was. I have vague recollections of it being something to do with the PL509 top cap. If you touch a few points in the circuit with a screwdriver it may change the position/pattern which might give you a clue. Peter

14th Sep 2015, 12:50 pm	#8
Dr-Watts Heptode Join Date: Dec 2006 Location: Milton Keynes, Buckinghamshire, UK. Posts: 696	Re: GEC Dual Standard Colour I restored one of these a while back and mine did the same. I never cured it either ! Dave W __________________ Do you have the scope to be a TV repair man

14th Sep 2015, 12:51 pm	#9
micheal Pentode Join Date: Mar 2007 Location: Croydon, London, UK. Posts: 111	Re: GEC Dual Standard Colour Way back in 1970 i had the 0.1u/f decoupler on the screen grid of line o/p valve PL509 go o/c but can't remember what fault it displayed, may be worth checking Mike

14th Sep 2015, 12:54 pm	#10
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: GEC Dual Standard Colour Micheal,it was striations (possibly I spelt it wrong) common also on Thorn mono were it was an o/c 1uF. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

14th Sep 2015, 2:28 pm	#12
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: GEC Dual Standard Colour Referring to the symptom mentioned in post #1. On the top cap of the line output valve, and also of the boost diode, there should be an anti Barkhausen oscillation choke. If one is missing or damage you can get a line down the screen, although I can't remember which side.

14th Sep 2015, 3:18 pm	#13
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: GEC Dual Standard Colour I remember permeability tuners in Bush TVs going back to the 405 line monochrome era. The cores were plastic rods with little ferrite sleeves spaced along them which moved along long formers wound with several coils. It's been a long time since I've seen one, but I think there was a core/former for band 1, and another for band 3, with one of those flat sliding multi-pole switches to select between them. On top of the tuner were the normal PCC84 and PCF80 type valves I remember one tuner that had the normal rotary selector with a cam arangement to operate the cores and switch. Another had 4 pushbuttons, 2 for band 1 the other 2 for band 3. Pressing a button operated the switch the right way and pressed on the end of the (spring-loaded) core to tune the thing.

14th Sep 2015, 6:52 pm	#14
Niechcial,Steve Hexode Join Date: Jan 2007 Location: Beckenham, London, UK. Posts: 373	Re: GEC Dual Standard Colour Thanks guys for the fault info. and the tuner discussion. I will check out those possibilities and report back.

14th Sep 2015, 8:04 pm	#15
Niechcial,Steve Hexode Join Date: Jan 2007 Location: Beckenham, London, UK. Posts: 373	Re: GEC Dual Standard Colour As Fernseh says, according to the manual R611 (1K) is on the convergence board. However in reality it is on the scan coils. It had gone up by 300R, and changing it has I think made things slightly better, but the striation is still there. The choke on the PY is fine. The circuit shows no choke fitted to the PL, but if someone can help me out with one from the scrap box, I'll try fitting it. I changed the screen grid de-coupler, but no joy there. I suppose I could also try a few ferrite beads around the place. I remember that sometime I the late 60s or 70s Practical television ran a whole article on BK oscillation. Last edited by AC/HL; 14th Sep 2015 at 11:14 pm. Reason: Several blank pages removed

14th Sep 2015, 8:27 pm	#16
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: GEC Dual Standard Colour I think you must have leaned on the CR key, lots of blank space in the post, can you still edit it? You should be able to make a coil for the top cap of the PL509, cannot remember exactly but half a dozen turns about 6 mm in diameter should do it. I seem to recall the boost diode top cap had them in some sets. Support the coil on a small piece of insulating material. Frank edit, missed the bit about the PY already having one, just make one like that for the PL

15th Sep 2015, 1:05 am	#17
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,967	Re: GEC Dual Standard Colour I had this problem a few times on the BRC1500 mono set, after changing the usual culprits I cleared the fault by replacing the 30FL2 line oscillated valve. So it might be worth changing the PCF802 line oscillated valve on your GEC colour set. __________________ Simon BVWS member

15th Sep 2015, 2:49 pm	#18
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 978	Re: GEC Dual Standard Colour Wasn't this called Barkenhausen Effect? I seem to remember sets that exhibited this could be fitted with a ferrite bead mounted as close to the anode of the line output bottle as you could. The early Decca hybrids suffered a lot (10 series) and I can remember curing a lot that way. Worth a try.

15th Sep 2015, 2:51 pm	#19
toshiba tony Heptode Join Date: May 2006 Location: Accrington, Lancashire, UK. Posts: 978	Re: GEC Dual Standard Colour Sorry, should have read all posts. Some other old timer beat me to it.

15th Sep 2015, 3:44 pm	#20
pichacker Hexode Join Date: Aug 2008 Location: Essex, UK. Posts: 370	Re: GEC Dual Standard Colour I had a 2040 when I was a lot younger and mine had a similar effect that could be influenced by moving wiring around. Mine turned out to be an open circuit stabilising VDR (Or similar device) in the centre of the line board. One end had been lifted during a previous repair by someone. I know the 2028 is different but hey you never know if you have a similar failed component. __________________ 6.3v on my heaters is no longer enough to get me going in the morning!!