Bush TV22 - Lack of width. - UK Vintage Radio Repair and Restoration Discussion Forum

DoctorWho · 24th Apr 2007, 11:16 am

I have a TV22 which is in superb condition and works very well, the only problem is lack of width.

It has been restored well, prior to me owning it, but the original Frame Blocking Transformer is completely missing and an incorrect substitute has been fitted. Is this likely to be the cause of the lack of width, or is it likely to be something else?

The width control does operate, but it doesn't take the picture to the edges of the CRT. This looks to be a Series I model as far as I can tell from the service data.

Any advice would be appreciated. I have placed an ad in the wanted section for the correct Frame Blocking Transformer, so if anyone can help on that score then please see the thread there.

Thanks for any help.

Peter.

Hunts smoothing bomb · 24th Apr 2007, 4:17 pm

Hello Peter,

I would almost certainly say that the lack of width is down to the incorrect transformer, I would say you will have your problem solved with the correct replacement. Is the line linarity affected too?
Good luck in obtaining the correct replacement.

Cheers
Lee

DoctorWho · 24th Apr 2007, 4:47 pm

Thanks Lee, I thought this may be the problem, the line linearity is pretty good actually, except for the very top of the picture, where things get a little jagged.

If anyone can help with a Frame Blocking Transformer I would be very grateful, please see my Wanted ad, or send me a PM. Thank you.

All the best,

Peter.

Heatercathodeshort · 24th Apr 2007, 9:12 pm

Am I going mad here? Please tell me if I need to activate my entry into the Victorian Home for Faded television Engineers...The frame blocking oscillator is going to effect the frequency of the vertical timebase [Frame]. If the vertical hold locks ok this is fine. It is the line output stage that needs looking at. I doubt if its valve trouble but it might be worth metering the H.T. for a start and if you have a PL38 to hand, give that a try. Is the picture nice and bright? Does it reduce in width as you turn the brightness up? I'm puzzled and getting too old.....
Regards John.

Hunts smoothing bomb · 24th Apr 2007, 9:38 pm

Yep! thanks John, I didn't read the post properly before I replied!
Just re-read it now.... Oh I feel like a

now

Sorry Peter! If you have full frame height with good linearity then I would suspect that the transformer you are using will be fine.......
Oh, my TV has just gone dead, must be the picture valve

Peter,
Are all the caps replaced around the line output stage, also resistors gone high can be the culprits.

Cheers
Lee

renato_enca · 24th Apr 2007, 10:48 pm

Hi, Peter.
Normally, in spite of valves having a high output impedance, the frame output transformer plays little role in the drive and linearity of the frame deflection coils, because the inductance of these transformers are "innofencive" to 50Hz signals. Think the transformer as a "coupler" between the deflection coil and the output valve, as done in the radio sets between the speaker and audio output valve. Even a audio output transformer should work, but ONLY at the FRAME output (no one expects driving a line scan coil with that - too much impedance).
Lee is right about the resistors: there used to be high value resistors on those output stages, which have the "natural" hability to rise up in value...even going O/C. Check those resistors and even, in last case, check if the deflection coil has been messed up(crazy ideia, but I've seen that before, someone needed 24SWG wire...).

Panrock · 24th Apr 2007, 11:07 pm

Are the PL38 and the PZ30 both tip-top?

These LOPTs can suffer from rusty laminations. Does it get unduly hot?

Have you tried optimising the position of the scan yoke fore-and-aft on the tube neck? Any adjustments may require re-setting the focus and the ion trap.

10 or 20 volts off the mains can make all the difference. Are the mains taps set correctly for your actual mains voltage? If all else fails, you might try reducing the HT tap (red wire) by one section to increase the HT and see what that does.

Steve

DoctorWho · 25th Apr 2007, 9:50 am

John - Don't go and put yourself in to a Victorian home, please

Both the horizontal and vertical hold lock fine. The picture is nice and bright yes, but it does reduce in width as the brightness control is turned up. What does this signify? I'll see if I have a spare PL38 and try that.

Lee - No worries, I'm grateful of the advice. All of the old wax condensers have been replaced. I haven't personally checked the resistors, are there any particular ones which you would check to begin with? Which resistors would be the classic ones to cause reduced width?

Renato - I'll check the resistors, see reply above. The deflection coils look untouched, so, hopefully, they should be alright.

Steve - I have to admit that I haven't done anything with the PL38 and the PZ30, I'll try replacements of both of these. The EY51 looks to have been replaced recently, and, as mentioned above, the picture is bright and with good focus. I haven't tried altering the position of the scan yoke, I'll investigate that. The mains tap is set for 250, I will also try decreasing this by 10 volts and see what happens.

Thanks again for the advice, I'll investigate along the lines suggested here. Any advice on which resistors to initially suspect would be appreciated.

Thanks again.

All the best,

Peter.

Hunts smoothing bomb · 25th Apr 2007, 10:41 am

Hello Peter,

I must admit I have never worked on this set so don't know it.
I would presume the LTB stage is fairly run of the mill stuff though so, (if it has one) I would check values of cathode and screen grid supply resistors on the PL38 and also the line oscillator valve, if the line oscillator valve is going low emision then it may not be giving enough drive into the grid of the PL38, if that was so I would have thought you would have a fairly hot and unhappy PL38 though.

Regards
Lee

DoctorWho · 25th Apr 2007, 2:50 pm

Thanks Lee, I'll do some investigating and see what the score is there.

Having had another look the CRT does not look to be the original, it has had a replacement fitted, which has been extremely well done, there is a seperate transformer for the heater (4 volts I think) and no ion trap. I can't yet find a CRT number. Would a different CRT lead to a lack of width? If so then what modifications would I need to make to overcome this?

Thanks again.

Peter.

Heatercathodeshort · 25th Apr 2007, 7:50 pm

Hello Peter,
Ok Peter, I was about to post the application but thought I would give you another chance. It will remain on the mantelpiece....

If turning the brightness up reduces the width, this is telling you that the line output stage is operating well under peak efficiency. Basically it cannot supply the few microamps of EHT required by the tube without reducing its output even further thus reducing the scan [width].

There can be many reasons for this and a few of the common ones have already been noted by our friends. First check the H.T. supply. It needs to be within around 10v of its quoted figure. The PL38 could be low emission but these are very reliable valves and rarely failed. A slight blue glow that varies with the line hold setting is quite normal by the way. They were over engineered and worked well within their limits. The line drive may be low caused by a faulty control grid coupling capacitor C17, the line oscillator valve itself [rare] or its anode load resistor gone high. This is R17 [Radio and TV servicing circuit] 820k and is a prime suspect. I expect the boost capacitor has been replaced, this is C21 a 2uf electrolytic.
C22 .2uf is another.

Failing this as mentioned, the line output transformer is suspect. A 100pf 8KV pulse capacitor connected from the PL38 top cap to chassis will bring the width out but of course this is the type of 'repair' I call 'Christmas Eve emergency' and is to be frowned upon....... A higher value say 180pf will give more width and a lower value say 50pf, less.
You will have to try a few to get it about right. This will reduce the eht and thus 'soften' the scanning beam. I have a few odd caps I can send you from my 405 days! I have more than I will ever use. If the CRT has a 4 volt heater it is probably a FERRANTI and will work well in the TV22. It will not effect raster size. Genuine Ferranti tubes were very well made and gave a long life. If it has an octal base it is probably a T9/3 or a T9/5 Regards John.

DoctorWho · 26th Apr 2007, 10:03 am

Hello John, I'm very pleased to hear that you decided against sending in the application, you have a lot of valued knowledge and are a great help

Thanks for explaining what's going on with the TV22, the old condensers have all been replaced, but I will check the condensers and the resistors you advise, especially R17. We have a friend staying for a few days, so if I don;t get the opportunity to check this before hand then I'll be able to get back to this next week. I'll let you know what I find out. I'll certainly check HT etc and see how it reads. Hopefully I'll be able to find a spare PL38 to try.

Thanks for the tip of adding a condenser between the top cap of the PL38 and chassis, I appreciate that this may not always be a repair that's looked upon kindly, but if something such as the LOPT is a bit rusted then it seems like a good solution to me. There's certaunly plenty of brightness on the CRT, so a slight reduction will, hopefully, not be a problem. Thanks for sending me a few caps, I appreciate that.

You're probably right about the CRT being a Ferranti, it does indeed have an Octal base.

Thanks again for the help and advice. I'll post more when I've worked through the suggestions.

All the best,

Peter.

beery · 26th Apr 2007, 1:20 pm

Hi Peter,
I would also replace the ECL80 in the line timebase as I think the triode section forms part of the line oscillator (from memory I think the pentode bit is the sync sep.). Have you seen the size of the triode section of an ECL80? How does it ever work??

Cheers
Andrew

DoctorWho · 26th Apr 2007, 8:08 pm

Thanks for the advice Andrew, I've just placed an order for an ECL80, so I'll try this, together with the new PL38 and see how things look.

Best regards,

Peter.

DoctorWho · 11th May 2007, 3:53 pm

Well I've now worked through this, thanks to John for the EHT condensers, I have now added one of these beneath the chassis and the problem is completely solved, the picture is full width, nice and bright and without any problems. Thanks to everyone who helped with this, and a special thank you to John for the EHT condensers.

24th Apr 2007, 11:16 am	#1
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Bush TV22 - Lack of width. I have a TV22 which is in superb condition and works very well, the only problem is lack of width. It has been restored well, prior to me owning it, but the original Frame Blocking Transformer is completely missing and an incorrect substitute has been fitted. Is this likely to be the cause of the lack of width, or is it likely to be something else? The width control does operate, but it doesn't take the picture to the edges of the CRT. This looks to be a Series I model as far as I can tell from the service data. Any advice would be appreciated. I have placed an ad in the wanted section for the correct Frame Blocking Transformer, so if anyone can help on that score then please see the thread there. Thanks for any help. Peter.

24th Apr 2007, 4:17 pm	#2
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Bush TV22 - Lack of width. Hello Peter, I would almost certainly say that the lack of width is down to the incorrect transformer, I would say you will have your problem solved with the correct replacement. Is the line linarity affected too? Good luck in obtaining the correct replacement. Cheers Lee __________________ Lee

24th Apr 2007, 4:47 pm	#3
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. Thanks Lee, I thought this may be the problem, the line linearity is pretty good actually, except for the very top of the picture, where things get a little jagged. If anyone can help with a Frame Blocking Transformer I would be very grateful, please see my Wanted ad, or send me a PM. Thank you. All the best, Peter.

24th Apr 2007, 9:12 pm	#4
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Bush TV22 - Lack of width. Am I going mad here? Please tell me if I need to activate my entry into the Victorian Home for Faded television Engineers...The frame blocking oscillator is going to effect the frequency of the vertical timebase [Frame]. If the vertical hold locks ok this is fine. It is the line output stage that needs looking at. I doubt if its valve trouble but it might be worth metering the H.T. for a start and if you have a PL38 to hand, give that a try. Is the picture nice and bright? Does it reduce in width as you turn the brightness up? I'm puzzled and getting too old..... Regards John.

24th Apr 2007, 9:38 pm	#5
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Bush TV22 - Lack of width. Yep! thanks John, I didn't read the post properly before I replied! Just re-read it now.... Oh I feel like a now Sorry Peter! If you have full frame height with good linearity then I would suspect that the transformer you are using will be fine....... Oh, my TV has just gone dead, must be the picture valve Peter, Are all the caps replaced around the line output stage, also resistors gone high can be the culprits. Cheers Lee __________________ Lee

24th Apr 2007, 10:48 pm	#6
renato_enca Retired Dormant Member Join Date: Feb 2007 Location: Lisbon, Portugal Posts: 51	Re: Bush TV22 - Lack of width. Hi, Peter. Normally, in spite of valves having a high output impedance, the frame output transformer plays little role in the drive and linearity of the frame deflection coils, because the inductance of these transformers are "innofencive" to 50Hz signals. Think the transformer as a "coupler" between the deflection coil and the output valve, as done in the radio sets between the speaker and audio output valve. Even a audio output transformer should work, but ONLY at the FRAME output (no one expects driving a line scan coil with that - too much impedance). Lee is right about the resistors: there used to be high value resistors on those output stages, which have the "natural" hability to rise up in value...even going O/C. Check those resistors and even, in last case, check if the deflection coil has been messed up(crazy ideia, but I've seen that before, someone needed 24SWG wire...).

24th Apr 2007, 11:07 pm	#7
Panrock Nonode Join Date: Feb 2005 Location: Worcestershire, UK. Posts: 2,535	Re: Bush TV22 - Lack of width. Are the PL38 and the PZ30 both tip-top? These LOPTs can suffer from rusty laminations. Does it get unduly hot? Have you tried optimising the position of the scan yoke fore-and-aft on the tube neck? Any adjustments may require re-setting the focus and the ion trap. 10 or 20 volts off the mains can make all the difference. Are the mains taps set correctly for your actual mains voltage? If all else fails, you might try reducing the HT tap (red wire) by one section to increase the HT and see what that does. Steve __________________ https://www.radiocraft.co.uk

25th Apr 2007, 9:50 am	#8
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. John - Don't go and put yourself in to a Victorian home, please Both the horizontal and vertical hold lock fine. The picture is nice and bright yes, but it does reduce in width as the brightness control is turned up. What does this signify? I'll see if I have a spare PL38 and try that. Lee - No worries, I'm grateful of the advice. All of the old wax condensers have been replaced. I haven't personally checked the resistors, are there any particular ones which you would check to begin with? Which resistors would be the classic ones to cause reduced width? Renato - I'll check the resistors, see reply above. The deflection coils look untouched, so, hopefully, they should be alright. Steve - I have to admit that I haven't done anything with the PL38 and the PZ30, I'll try replacements of both of these. The EY51 looks to have been replaced recently, and, as mentioned above, the picture is bright and with good focus. I haven't tried altering the position of the scan yoke, I'll investigate that. The mains tap is set for 250, I will also try decreasing this by 10 volts and see what happens. Thanks again for the advice, I'll investigate along the lines suggested here. Any advice on which resistors to initially suspect would be appreciated. Thanks again. All the best, Peter.

25th Apr 2007, 10:41 am	#9
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Bush TV22 - Lack of width. Hello Peter, I must admit I have never worked on this set so don't know it. I would presume the LTB stage is fairly run of the mill stuff though so, (if it has one) I would check values of cathode and screen grid supply resistors on the PL38 and also the line oscillator valve, if the line oscillator valve is going low emision then it may not be giving enough drive into the grid of the PL38, if that was so I would have thought you would have a fairly hot and unhappy PL38 though. Regards Lee __________________ Lee

25th Apr 2007, 2:50 pm	#10
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. Thanks Lee, I'll do some investigating and see what the score is there. Having had another look the CRT does not look to be the original, it has had a replacement fitted, which has been extremely well done, there is a seperate transformer for the heater (4 volts I think) and no ion trap. I can't yet find a CRT number. Would a different CRT lead to a lack of width? If so then what modifications would I need to make to overcome this? Thanks again. Peter.

25th Apr 2007, 7:50 pm	#11
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Bush TV22 - Lack of width. Hello Peter, Ok Peter, I was about to post the application but thought I would give you another chance. It will remain on the mantelpiece.... If turning the brightness up reduces the width, this is telling you that the line output stage is operating well under peak efficiency. Basically it cannot supply the few microamps of EHT required by the tube without reducing its output even further thus reducing the scan [width]. There can be many reasons for this and a few of the common ones have already been noted by our friends. First check the H.T. supply. It needs to be within around 10v of its quoted figure. The PL38 could be low emission but these are very reliable valves and rarely failed. A slight blue glow that varies with the line hold setting is quite normal by the way. They were over engineered and worked well within their limits. The line drive may be low caused by a faulty control grid coupling capacitor C17, the line oscillator valve itself [rare] or its anode load resistor gone high. This is R17 [Radio and TV servicing circuit] 820k and is a prime suspect. I expect the boost capacitor has been replaced, this is C21 a 2uf electrolytic. C22 .2uf is another. Failing this as mentioned, the line output transformer is suspect. A 100pf 8KV pulse capacitor connected from the PL38 top cap to chassis will bring the width out but of course this is the type of 'repair' I call 'Christmas Eve emergency' and is to be frowned upon....... A higher value say 180pf will give more width and a lower value say 50pf, less. You will have to try a few to get it about right. This will reduce the eht and thus 'soften' the scanning beam. I have a few odd caps I can send you from my 405 days! I have more than I will ever use. If the CRT has a 4 volt heater it is probably a FERRANTI and will work well in the TV22. It will not effect raster size. Genuine Ferranti tubes were very well made and gave a long life. If it has an octal base it is probably a T9/3 or a T9/5 Regards John.

26th Apr 2007, 10:03 am	#12
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. Hello John, I'm very pleased to hear that you decided against sending in the application, you have a lot of valued knowledge and are a great help Thanks for explaining what's going on with the TV22, the old condensers have all been replaced, but I will check the condensers and the resistors you advise, especially R17. We have a friend staying for a few days, so if I don;t get the opportunity to check this before hand then I'll be able to get back to this next week. I'll let you know what I find out. I'll certainly check HT etc and see how it reads. Hopefully I'll be able to find a spare PL38 to try. Thanks for the tip of adding a condenser between the top cap of the PL38 and chassis, I appreciate that this may not always be a repair that's looked upon kindly, but if something such as the LOPT is a bit rusted then it seems like a good solution to me. There's certaunly plenty of brightness on the CRT, so a slight reduction will, hopefully, not be a problem. Thanks for sending me a few caps, I appreciate that. You're probably right about the CRT being a Ferranti, it does indeed have an Octal base. Thanks again for the help and advice. I'll post more when I've worked through the suggestions. All the best, Peter.

26th Apr 2007, 1:20 pm	#13
beery Heptode Join Date: Jun 2006 Location: Ware, Hertfordshire, UK. Posts: 988	Re: Bush TV22 - Lack of width. Hi Peter, I would also replace the ECL80 in the line timebase as I think the triode section forms part of the line oscillator (from memory I think the pentode bit is the sync sep.). Have you seen the size of the triode section of an ECL80? How does it ever work?? Cheers Andrew

26th Apr 2007, 8:08 pm	#14
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. Thanks for the advice Andrew, I've just placed an order for an ECL80, so I'll try this, together with the new PL38 and see how things look. Best regards, Peter.

11th May 2007, 3:53 pm	#15
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Bush TV22 - Lack of width. Well I've now worked through this, thanks to John for the EHT condensers, I have now added one of these beneath the chassis and the problem is completely solved, the picture is full width, nice and bright and without any problems. Thanks to everyone who helped with this, and a special thank you to John for the EHT condensers.