UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Reply
 
Thread Tools
Old 13th Oct 2019, 10:48 am   #161
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,942
Default Re: Bush TV22 with TC184 B3 converter.

Last night a substitute frame blocking transformer was tried out in the TV32.
The transformer chosen for the Bush TV32 is a Radiospares FT7 which was made as an exact replacement for the HMV 1824 series.
The frame oscillator is working again, plenty picture height adjustment and the frame hold locks in the centre position of the control.
But the set has problems with interlace. The preset interlace control VR9 can be adjusted for good interlace but the setting is critical and not reliable.

Extract from #154 Argus25 wrote:
"The circuits with the Westector diode in the TV22 are interesting. If you assume the diode has around 100k leakage or less (would be interesting to measure it) the average diode anode voltage would simply climb to the plate circuit voltage of the sync sep stage. Then when the leading edge of a negative going pulse appeared the diode would assume a low resistance and when the plate voltage went high again the diode would stop conducting and go back into leakage mode acting like a high value resistor.
So it appears as if the designers wanted a filter with a fast attack and a slow decay. Which to some extent makes sense and another not."

Note the HMV frame timebase circuit has an interlace diode with a 2.2Mohm resistor connected in parallel.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	BushTV32_FOT_2.jpg
Views:	91
Size:	95.6 KB
ID:	191810   Click image for larger version

Name:	BushTV32_FOT_3.jpg
Views:	108
Size:	57.5 KB
ID:	191811   Click image for larger version

Name:	BushTV32_FOT_4.jpg
Views:	84
Size:	59.5 KB
ID:	191812   Click image for larger version

Name:	BushTV32_FOT_5.jpg
Views:	119
Size:	169.8 KB
ID:	191813  

Last edited by FERNSEH; 13th Oct 2019 at 10:54 am.
FERNSEH is offline   Reply With Quote
Old 14th Oct 2019, 10:09 pm   #162
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,942
Default Re: Bush TV22 with TC184 B3 converter.

The replacement blocking oscillator transformer is now permanently fitted on the chassis. As the Radiospares transformer is slightly larger than the original this necessitated that two holes had to be drilled in the chassis.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	BushTV32_FOT_6.jpg
Views:	104
Size:	152.8 KB
ID:	191943  
FERNSEH is offline   Reply With Quote
Old 15th Oct 2019, 1:25 am   #163
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

Regardless of the quality suitability of the integrator and interlace diode design in this set, I would expect the interlace to be pretty poor. The set looks like its still running original electros and the HT rail will be buzzing with H pulses and probably C67 is high ESR too letting these into the vertical oscillator and fouling up the interlace. Clearly the V oscillator is getting triggered by H pulses and not the leading edge of the V sync pulse, so your half line delay is going down the toilet.
Argus25 is offline   Reply With Quote
Old 15th Oct 2019, 3:30 pm   #164
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,942
Default Re: Bush TV22 with TC184 B3 converter.

AC ripple on the HT line is 2 volts P - P.
The TV32 has a 3microfarad ripple cancelling capacitor in series with a 2.9Kohm high wattage resistor.
The two components are connected between the top of the heater chain and the HT rail.

DFWB.
FERNSEH is offline   Reply With Quote
Old 15th Oct 2019, 3:41 pm   #165
peter_scott
Nonode
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 2,225
Default Re: Bush TV22 with TC184 B3 converter.

Hi David,

My far from perfect TV32 has 600mV p-p ripple on the HT but that is with modern electrolytics.

Peter
peter_scott is offline   Reply With Quote
Old 15th Oct 2019, 3:43 pm   #166
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,942
Default Re: Bush TV22 with TC184 B3 converter.

Hi Peter, have just checked the ripple cancelling capacitor on a capacitance meter and multi-meter high ohms range. The capacitor is useless!

DFWB.
FERNSEH is offline   Reply With Quote
Old 15th Oct 2019, 3:53 pm   #167
peter_scott
Nonode
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 2,225
Default Re: Bush TV22 with TC184 B3 converter.

Is the 3uF on the top side of the chassis? If so I've not changed mine as I've not taken the chassis out of the cabinet. Ah! found it. Not changed.

Peter

Last edited by peter_scott; 15th Oct 2019 at 4:03 pm.
peter_scott is offline   Reply With Quote
Old 15th Oct 2019, 4:00 pm   #168
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,942
Default Re: Bush TV22 with TC184 B3 converter.

Hi Peter, yes, the 3mfd capacitor is on the topside of the chassis. The chassis will have to come to gain access to it.
As a temporary measure I've tacked in a 4mfd motor run capacitor and the ripple is now a distorted sine wave and is down to 1volt P - P.
Fit a capacitor of the correct value and the ripple should be reduced further.

DFWB.
FERNSEH is offline   Reply With Quote
Old 5th Dec 2019, 1:07 am   #169
Helder Crespo
Triode
 
Helder Crespo's Avatar
 
Join Date: Sep 2019
Location: Porto, Portugal
Posts: 38
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by peter_scott View Post
I have just changed R52 (on the Trader Sheet) from 100k to 10k and it looks like that is all that is required to obtain interlacing. If anyone is wondering why alternate lines are dim this simply the persistence of the phosphor and the camera shutter not being open long enough to average out the light from the two scans. In the first photo the rightmost image of the group of three is the TV22 with 10k. I've added a close-up of the 10k photo. Then another of the 100k.

Peter
Hi. Do you recommend changing R52 from 100k to 100k on any TV22 in order to get proper interlacing?
Helder Crespo is offline   Reply With Quote
Old 5th Dec 2019, 2:48 am   #170
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Helder Crespo View Post

Hi. Do you recommend changing R52 from 100k to 100k on any TV22 in order to get proper interlacing?
As I pointed out there was a design error in the TV22 in that the V sync was grossly over integrated. So the 100k needs reducing, in the circuit as it stands, if you want to have better interlace. Another option is to change it to around 15k and replace the diode with a 15k resistor, will give a good two stage filter.

Still the interlace will possibly be poor if the HT filter caps are in poor condition (the originals always are in poor condition) or the the hum cancelling cap off value. So it is important to rebuild the capacitors for a good result.
Argus25 is offline   Reply With Quote
Old 5th Dec 2019, 10:52 am   #171
Helder Crespo
Triode
 
Helder Crespo's Avatar
 
Join Date: Sep 2019
Location: Porto, Portugal
Posts: 38
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Argus25 View Post
Quote:
Originally Posted by Helder Crespo View Post

Hi. Do you recommend changing R52 from 100k to 100k on any TV22 in order to get proper interlacing?
As I pointed out there was a design error in the TV22 in that the V sync was grossly over integrated. So the 100k needs reducing, in the circuit as it stands, if you want to have better interlace. Another option is to change it to around 15k and replace the diode with a 15k resistor, will give a good two stage filter.

Still the interlace will possibly be poor if the HT filter caps are in poor condition (the originals always are in poor condition) or the the hum cancelling cap off value. So it is important to rebuild the capacitors for a good result.
Thanks! I had read this thread thoroughly and indeed it seems like an intrinsic design error. Your explanation to why it went uncorrected is also very plausible, and the changes seen in the following Bush models indicate that they must have been aware of the issue, which furthermore is easier to spot in sets with larger tubes and hence smaller line densities. I will be testing this mod soon, as my TV22 has recently been recapped so all caps are good and with the right values. Should this "mod"/correction enable using the Aurora’s equalisation pulse mode, which to my knowledge is not beneficial when feeding a standard TV22?
Helder Crespo is offline   Reply With Quote
Old 5th Dec 2019, 12:07 pm   #172
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Helder Crespo View Post
Should this "mod"/correction enable using the Aurora’s equalisation pulse mode, which to my knowledge is not beneficial when feeding a standard TV22?
Equalization pulses normally help the probability of a good interlace, regardless of how good or poor the vertical integrator is. Ideally you have a good multi-stage, two or three stage RC integrator and the equalization pulses present in the sync too and the scenario is optimized for perfect interlace. This was standard practice for American TV sync signals immediately post WW2 and their TV sets seldom had any interlace issues as a result. If the vertical integrator is a poor design to the extreme, then, the equalization pulses cannot help.That is why they are not beneficial for the standard TV22
Argus25 is offline   Reply With Quote
Old 5th Dec 2019, 12:50 pm   #173
Helder Crespo
Triode
 
Helder Crespo's Avatar
 
Join Date: Sep 2019
Location: Porto, Portugal
Posts: 38
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Argus25 View Post
Quote:
Originally Posted by Helder Crespo View Post
Should this "mod"/correction enable using the Aurora’s equalisation pulse mode, which to my knowledge is not beneficial when feeding a standard TV22?
Equalization pulses normally help the probability of a good interlace, regardless of how good or poor the vertical integrator is. Ideally you have a good multi-stage, two or three stage RC integrator and the equalization pulses present in the sync too and the scenario is optimized for perfect interlace. This was standard practice for American TV sync signals immediately post WW2 and their TV sets seldom had any interlace issues as a result. If the vertical integrator is a poor design to the extreme, then, the equalization pulses cannot help.That is why they are not beneficial for the standard TV22
Thank you very much for your detailed and very clear reply. In view of this, and the other information on this thread (namely your analysis on why the pulse characteristics achieved with the diode and over integration can actully make sense for a system without equalising pulses, as in uk broadcasts), it seems beneficial to perform the "mod", either to reduce the time constant (by simply replacing R52 with a lower value), or to achieve a much more effective dual-stage filter with two 15k resistors, where in both cases it should be possible to find ideal values empirically for any particular set with the help of a pot. I recently noticed interlacing differences when comparing different TV22s and other Bush models in operation, and if these can be solved/equalised while ending up with a system that can also take advantage of the features of modern converters (namely the equalising pulse option in the Aurora), this seems like the way to go. This should only add capabilities to the set, without significantly detracting from its originally, as the change is minimally intrusive, IMO.
Helder Crespo is offline   Reply With Quote
Old 5th Dec 2019, 1:53 pm   #174
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Helder Crespo View Post
Thank you very much for your detailed and very clear reply.
Thank you.

There is a very good description of equalizing pulses and their application in Principles of Television Engineering, by Donald Fink, McGraw-Hill, 1940.

He points out that the purpose of the equalizing pulses is to make the shape of each vertical pulse the same, after separation. The shape otherwise is not the same as in one case the vertical sync block starts with a 1 line delay from the preceding H pulse and on the next field a 1/2 line delay. The equalizing pulses fix this issue.

Still, even without this issue fixed, it is still possible to have a respectable interlace. They also recommend that the filtering is not so heavy that the serrations are completely removed from the V sync, but I have found the interlace is fine if they are filtered to the extent that they are just removed as shown by V sync recordings from RCA, but gross over integration is a bad idea. Also, two stage integrators were being shown at this point in time in the American literature.
Argus25 is offline   Reply With Quote
Old 5th Dec 2019, 8:13 pm   #175
Helder Crespo
Triode
 
Helder Crespo's Avatar
 
Join Date: Sep 2019
Location: Porto, Portugal
Posts: 38
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Argus25 View Post
Quote:
Originally Posted by Helder Crespo View Post
Thank you very much for your detailed and very clear reply.
Thank you.

There is a very good description of equalizing pulses and their application in Principles of Television Engineering, by Donald Fink, McGraw-Hill, 1940.

He points out that the purpose of the equalizing pulses is to make the shape of each vertical pulse the same, after separation. The shape otherwise is not the same as in one case the vertical sync block starts with a 1 line delay from the preceding H pulse and on the next field a 1/2 line delay. The equalizing pulses fix this issue.

Still, even without this issue fixed, it is still possible to have a respectable interlace. They also recommend that the filtering is not so heavy that the serrations are completely removed from the V sync, but I have found the interlace is fine if they are filtered to the extent that they are just removed as shown by V sync recordings from RCA, but gross over integration is a bad idea. Also, two stage integrators were being shown at this point in time in the American literature.
Thanks! I found the book online here: https://www.americanradiohistory.com...-Fink-1940.pdf
Helder Crespo is offline   Reply With Quote
Old 6th Dec 2019, 7:04 am   #176
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

It is an interesting situation in that the American TV engineers were years ahead of the ones in the UK in the 1940's, with designs that included energy efficiency scanning and proper interlace systems.

The paradox is though, that many of the revolutionary ideas about TV technology in fact originated in the UK, from people like Blumlein. However they were only paid attention to in the USA initially, for example RCA labs taking up Blumlein's idea for energy recovery scanning in the early 1940's.

So UK TV's were slow to get these improvements, along with slow to get turret tuners as well compared to their American counterparts.

The same thing repeated itself in the field of computing where the theory in the UK was well ahead in the 1950's, but more successfully commercialized in the USA. I guess they had the population to support this.
Argus25 is offline   Reply With Quote
Old 6th Dec 2019, 9:50 am   #177
Helder Crespo
Triode
 
Helder Crespo's Avatar
 
Join Date: Sep 2019
Location: Porto, Portugal
Posts: 38
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Argus25 View Post
It is an interesting situation in that the American TV engineers were years ahead of the ones in the UK in the 1940's, with designs that included energy efficiency scanning and proper interlace systems.

The paradox is though, that many of the revolutionary ideas about TV technology in fact originated in the UK, from people like Blumlein. However they were only paid attention to in the USA initially, for example RCA labs taking up Blumlein's idea for energy recovery scanning in the early 1940's.

So UK TV's were slow to get these improvements, along with slow to get turret tuners as well compared to their American counterparts.

The same thing repeated itself in the field of computing where the theory in the UK was well ahead in the 1950's, but more successfully commercialized in the USA. I guess they had the population to support this.
I'm sure there are many examples of other industrial and technological developments where different countries moved at different paces and in different directions, regardless of the origins, tradition, know-how and even patents related to a given technology or product. As you point out, the population is also important, as well as the whole economy, as both are determinant for the growth potential (education --> research --> development --> industry) and also relate to the size of the potential internal market. Perhaps american companies were more risk prone, and when you have a big market to start with, any new solutions that are more reliable and/or efficient (e.g., the energy efficient scanning) can be very appealing within the context of an economy of scale.
Helder Crespo is offline   Reply With Quote
Old 6th Dec 2019, 11:30 am   #178
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,680
Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Helder Crespo View Post
Perhaps american companies were more risk prone, and when you have a big market to start with, any new solutions that are more reliable and/or efficient (e.g., the energy efficient scanning) can be very appealing within the context of an economy of scale.
I think that is correct.

When FM was invented RCA knew that people would not bring their AM radios back in for modification, so instead they more or less trialed it by bringing it out immediately post WW2, in their first post war TV set, the 621TS and quickly they moved to FM sound for all TV transmissions, while AM sound for TV persisted in other countries for a decade or more.

FM sound for radios initially was popularized in car radios before it really took off and now it is being exterminated by digital radio, which has inferior quality.

Coming from a small country like NZ, by the time we adopted any new tech in those says it was already mature, and we got monochrome TV, with FM sound around 1958-1960.

I was amazed when I first saw a TV set with AM sound in NZ, it was imported from the UK (didn't work in NZ of course) I had to modify the scan stages and convert the detector to FM and because the set was a TRF I had to hang a turret tuner on its front end to get it to work. The self oscillating line output stage was a challenge, I sped it up by parting the two halves of the line output transformer's core to make it run at 15,625 KHz.
Argus25 is offline   Reply With Quote
Old 6th Dec 2019, 3:26 pm   #179
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 6,984
Default Re: Bush TV22 with TC184 B3 converter.

I have a Stromberg Carlson radiogram dating from 1941 with FM on the 40-45 mc/s band.
I believe it was changed to 88-108mc/s immediately after WW2.
The FM unit is a separate chassis with octal valves! John.
Heatercathodeshort is offline   Reply With Quote
Old 6th Dec 2019, 7:45 pm   #180
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 934
Default Re: Bush TV22 with TC184 B3 converter.

Had to take my TV22 MKII out of the case today to replace a crackly audio o/p transformer (a shorted turn I suspect) and took the opportunity of reducing R52 (R55 in the MKII) to 10k. I really couldn't see any difference, except the picture made a slight twitch as I did it.

Anyway, I think the picture is probably as good as the TV22 gets. I'm lucky with the tube, although it does need a slight refocussing after the first 30 mins or so.

Rather a nice set, and MUCH easier to work on the the TV24!

Photo of picture with 100k resistor:
Attached Thumbnails
Click image for larger version

Name:	20191206_183154[1].jpg
Views:	58
Size:	58.8 KB
ID:	194970  
Ian - G4JQT is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 11:54 pm.


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 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.