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 > Specific Vintage Equipment > Vintage Television and Video

Notices

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

Closed Thread
 
Thread Tools
Old 9th Jan 2021, 6:05 pm   #1
jhalphen
Hexode
 
Join Date: Jul 2004
Location: Paris, France
Posts: 271
Default Risks involved using a 441 line TV on 625 ?

Good day Gentlemen,

A French vintage TV collector is planning on alternate use of an Aurora SCRF819E converter from its initial purpose : converting 625 to 819 with RF modulation.

The Aurora can be used in bypass mode, ie 625 video is passed on directly to the RF mod without standards conversion. Channel 1 is on 42 & 46 MHz, the original Paris pre-war frequency.

Question: What are the risks involved (if any) asking the TV's H section to run at 625 vs 441 ?
I presume so far that the TVs have line-derived EHT and not the Flyback type.

If a flyback; dangerous to the LOPT ?

I am waiting for the precise TV receiver models.
Will update when known.

Thank you! in advance for comments & suggestions,

Best Regards
jhalphen
Paris/France
jhalphen is offline  
Old 9th Jan 2021, 8:02 pm   #2
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,020
Default Re: Risks involved using a 441 line TV on 625 ?

Hello Jerome,
will the collector be supplying the signals to more than one 441 line receiver?
The line frequency of the 441 line system is 11,025Hz, a picture line will have duration of 90.7microseconds compared with 64us of the 625 line system.
If the 441 line receiver has flyback derived EHT I would guess real problem will be lack of width and low EHT.
Receivers with a separate EHT source might work after some adjustment to the line drive waveform at the grid of the line output valve.

There is a Philips TF390A in the shop which works fine on 405 but let's find out how things go if it is supplied with a 625 signal.

DFWB.

Last edited by FERNSEH; 9th Jan 2021 at 8:11 pm.
FERNSEH is offline  
Old 9th Jan 2021, 9:31 pm   #3
jhalphen
Hexode
 
Join Date: Jul 2004
Location: Paris, France
Posts: 271
Default Re: Risks involved using a 441 line TV on 625 ?

Hi to all,
Hello David, Thanks! for the reply.

The converter is purchased primarely to operate 819 line TVs.

However, as a bonus, it includes Channel 1 (42 & 46 MHz) hence the idea to try with a 441 set.

I don't have the collector's answer yet about makes & models, but i'm pretty sure he only has one 441 set.

So it's only a bonus, not the main purpose.

Best Regards
jhalphen
Paris/France
jhalphen is offline  
Old 10th Jan 2021, 4:51 pm   #4
rambo1152
Dekatron
 
rambo1152's Avatar
 
Join Date: May 2010
Location: Manchester, UK.
Posts: 3,359
Default Re: Risks involved using a 441 line TV on 625 ?

French 441 is very similar to the UK 405 line system, both having +ve modulation.

A few of us use a PC with a suitable graphics card and use the legacy Modeline instruction to create the required TV waveform.

Modeline "405i50" 8.10 664 680 752 800 377 378 385 405 -hsync -vsync interlace
creates a native 405 line picture on my Cossor 405 line set

Click image for larger version

Name:	405.jpg
Views:	126
Size:	56.3 KB
ID:	224282

Changing the modeline to 441 lines as suggested by forum member Semir_DE
Modeline "656x383_25 11.0kHz 50.0Hz" 8.820 656 665 744 800 383 384 392 441 -hsync -vsync interlace

Click image for larger version

Name:	441a.jpg
Views:	123
Size:	62.2 KB
ID:	224283

And a slight tweak of the horizontal hold from 10124 to 11025Hz and we have a locked 441 line picture. No expensive "system converter" in sight, and it doesn't require my source material to be in a particular analogue format.

Click image for larger version

Name:	441 b.jpg
Views:	146
Size:	53.6 KB
ID:	224284

Running a rare historically significant set on the wrong standard seems almost sacrilegious to me, but perhaps I attach far too much reverence to these old sets.
__________________
--
Graham.
G3ZVT

Last edited by rambo1152; 10th Jan 2021 at 5:15 pm.
rambo1152 is offline  
Old 10th Jan 2021, 5:56 pm   #5
Guest
Guest
 
Posts: n/a
Default Re: Risks involved using a 441 line TV on 625 ?

A British set showing a French standard, that's rather "international" (in a good way). I do wonder if anyone either side of the channel got the other sides signals and tweaked the horizontal hold to see the picture?
 
Old 10th Jan 2021, 6:43 pm   #6
peter_scott
Dekatron
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,080
Default Re: Risks involved using a 441 line TV on 625 ?

http://www.earlytelevision.org/raf.html
peter_scott is online now  
Old 10th Jan 2021, 10:01 pm   #7
stainless
Tetrode
 
Join Date: Jun 2006
Location: London, UK.
Posts: 53
Default Re: Risks involved using a 441 line TV on 625 ?

When I was young, living in Bedford, (mid 60s), I did once pick up French 819 (would it have been on Band I, channel 4 or the like?), and adjusted the line hold to give me two pictures side by side. No idea if it was locking on the correct edge of the sync - didn't know about such things in those days!
__________________
If you can have 4.7 MHz, why can't you have 4.7 MOm!
stainless is offline  
Old 11th Jan 2021, 9:32 am   #8
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,015
Default Re: Risks involved using a 441 line TV on 625 ?

Hi.
Running the line time base at 15625hz is not a good thing to do. Firstly the time base is optimised for 441 lines. Simply increasing the line speed will result in lack of width and low EHT if its a flyback generated EHT. Resultant current through the line output valve and boost diode will rise as will current in the LOPT which may saturate too, you'll also get foldover on the left hand side of the picture.
Some component value changes in the line oscillator could improve the line drive waveform that will help. I'd then say you may be able to get a reasonable result but you could find currents in the output stage are still a bit high.
I modified a Pye V4 many years back for 625 and after sorting out the oscillator the picture was good but the LOPT failed after a few weeks.
TBH I'd not modify the line stage especially if there is no chance of a spare LOPT.
__________________
Cheers,
Trevor.
2M0GZQ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 11th Jan 2021, 4:18 pm   #9
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,020
Default Re: Risks involved using a 441 line TV on 625 ?

The 441 line Philips TF390A is fine on the 405 line standard but doesn't work at all well well on 625 lines. A dim picture with bad focus.
The attachment shows the set operating on 405 lines.
The Aurora SCRF405A converter is being supplied from a separate signal source.

DFWB.
Attached Thumbnails
Click image for larger version

Name:	DSC_0487[1].jpg
Views:	119
Size:	49.4 KB
ID:	224389  
FERNSEH is offline  
Old 11th Jan 2021, 4:24 pm   #10
Panrock
Nonode
 
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,265
Default Re: Risks involved using a 441 line TV on 625 ?

Wow! That's a nice set. What year is it?

Steve
__________________
www.radiocraft.co.uk
Panrock is offline  
Old 11th Jan 2021, 4:42 pm   #11
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,020
Default Re: Risks involved using a 441 line TV on 625 ?

Hi Steve,
I'd guess 1949 or 50. The TF390A is similar to the UK made Philips 385U. Main difference is the French set has a double wound mains transformer so that it can be used on 110 to 130 volt mains supplies.
Like the 385U it has 0.1amp valves in three heater chains. CRT is a Philips MW22-14.
Set was made in Holland.

DFWB.
FERNSEH is offline  
Old 11th Jan 2021, 6:18 pm   #12
jhalphen
Hexode
 
Join Date: Jul 2004
Location: Paris, France
Posts: 271
Default Re: Risks involved using a 441 line TV on 625 ?

Hello to all,

Thank You ! very much for your replies, lots of experience & great knowledge here.

Fernseh, David, many Thanks ! for taking the time to test the Philips TF390 TV.
The French forum member has the same one.
Your test shows clearly that it should NOT be used on 625.

He also has a Grammont 178C7 441 line model. Interestingly, it has been modified post-WWII to use a flyback (LOPTY) EHT generator.
Don't know if it's a factory-mod, or done in the field. Maybe the power transformer EHT overwind went open and the part was unavaible.

And so, thanks to your tests, he has now decided to acquire an Aurora SCRF441 specifically for sets using this lineage.

Best Regards
jhalphen
Paris/France
jhalphen is offline  
Old 11th Jan 2021, 8:15 pm   #13
FERNSEH
Dekatron
 
FERNSEH's Avatar
 
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,020
Default Re: Risks involved using a 441 line TV on 625 ?

Hi Jerome,
Even if the line timebases of the 441 line receivers were modified to work satisfactorily on 625 lines the horizontal definition would be degraded because the video bandwidth in the Paris Tx receivers is limited to 3.5Mhz.

Worth mentioning is the number of active lines in the 441 line system was almost most the same as the 405 line system.
The 441 frame blanking period is very much longer than 28 lines in the 405 system.

DFWB..
FERNSEH is offline  
Old 16th Jan 2021, 5:43 pm   #14
Andy Green
Hexode
 
Join Date: Jan 2005
Location: Waterford, Republic of Ireland
Posts: 256
Default Re: Risks involved using a 441 line TV on 625 ?

Quote:
Originally Posted by merlinmaxwell View Post
A British set showing a French standard, that's rather "international" (in a good way). I do wonder if anyone either side of the channel got the other sides signals and tweaked the horizontal hold to see the picture?
When I lived in Sussex, we regularly used to get B1French 819 Line TV wiping out BBC1, and I recall, after tweaking the horizontal hold a bit, it looked like two narow pictures side by side.
many years later, (in 2007) I bought a French 819 Line TV and fed it a 405 Line signal from an Aurora to see what it looked like. It looked very similar actually. See https://www.vintage-radio.net/forum/...ad.php?t=17342
Andy Green is offline  
Closed Thread

Thread Tools



All times are GMT. The time now is 9:40 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 - 2022, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.