Decca 1000 Projection TV Pre-restoration Advice Request. - UK Vintage Radio Repair and Restoration Discussion Forum

DoctorWho · 29th May 2007, 6:56 pm

I have recently been given a Decca 1000 Projection TV set which is in pretty good condition. The set looks complete and the only modification I can see is the addition of a 12-channel turret tuner, probably in the mid 1950's.

I just wanted to ask if there are any special tips anyone can give me for restoring these sets as I have not worked on one of these sets before?

I see that the EHT unit generates 25kv, do the EHT condensers have to be replaced in this unit? If so, which ones?

I have found the electronic focus control, but not the manual focus control. I see that there are two large knobs around the projection lens, are these for focus or for positioning of the picture? I'd be grateful of an explanation as to how you manually focus the picture on these sets if possible please.

Anything else in particular I should be looking out for with this set? What's the best way to remove the various chassis and what's the best way to test the set?

Any advice appreciated.

Peter.

tvden · 29th May 2007, 7:11 pm

This set should not be operated out of its box, as it produces X-Rays.

DoctorWho · 29th May 2007, 7:21 pm

Thanks for the warning Den, what part of the circuitry produces the X-rays?

ppppenguin · 29th May 2007, 7:36 pm

Only the CRT produces X-rays. Enough to be harmful at close range.

ppppenguin · 29th May 2007, 8:00 pm

The EHT in these sets is 25kV but it's from an RF unit so it's not particularly dangerous as there's not a lot of current available. Even 2kV from a mains transformer is a lot nastier. As with any high voltage I still wouldn't recommend touching it on purpose.

Framer Dave · 29th May 2007, 9:17 pm

Hello Peter,

The EHT condensers (and the 3 EY51s in the tripler) are within an oil-filled can. This is sealed and would be difficult to work on. They do seem to have a good survival rate though and are usually working OK. Trader Service Sheet 1119 covers the EHT unit and 1118 the optical parts, including CRT replacement.

Based on personal experience, I wouldn't twiddle any knobs before reading the above!

An interesting set. Best of luck with the restoration.

Regards,

Dave

DoctorWho · 29th May 2007, 10:17 pm

Jeffrey - Thanks for clarifying, does this also include the optical lens at the front, or simply the area around the CRT inside the set?

Den - Having looked at the various chassis within the set I don't think I will need to remove the CRT, so that's great. I presume inside the set there's little danger outside or from the front or back?

Jeffrey - Thanks for explaining about the RF EHT. I will avoid touching it though!

Dave - Thanks for explaining about the EHT condensers and the three EY51's, from what you have said am I right to presume that you can't change the EY51's if they are in a sealed oil filled can? Presumably PCB oil? I hope the EY51's are good then. I'll leave this can assembly well alone I think! Thanks for letting me know which service data sheets to work from. I will certainly read the above before starting work on the set.

Anyone know how to manually adjust the focus if it is outside the range of the electronic focus control? This is the one thing I haven't yet worked out?

A comment has been made that this looks like an elaborate tea trolley, certainly it is most unusual with the drop down flap. I'll report back how the restoration goes.

Thanks again for the advice.

Peter.

Steve_P · 29th May 2007, 11:06 pm

If the frame output goes, then the tube will (hopefully) be turned off. This is because the Single White Line would literally burn itself into the tube.

Disable the EHT at first plug in. Having a quick look at the circuit, I would try disconnecting the HT to the EHT Unit - Pin 5 on the 'A' Plug.

If you want the circuit, it's on Duke Nukem's CD-ROM, available at his site:

http://www.thevalvepage.com/servdata/servdata.htm

Cheers,

Steve P

Duke_Nukem · 30th May 2007, 8:30 am

Full details of the optical unit here (shameless plug):-

http://www.thevalvepage.com/teletech...art1/part1.htm

Note that it is possible that there might be different versions of the EHT generator.

I would echo other comments and disconnect the EHT unit (or at least disable it) as if either timebase fails it could burn the phosphor very quickly indeed. There should be a protection circuit for this but during initial work I certainly wouldn't want to rely on it.

TTFN,
Jon

PS : If needed, I do have a pucka manual somewhere for this set awaiting scanning - it's an awkward pain-in-the-wotsit size which makes scanning awkward, I guess this is why its towards the bottom of the pile.

beery · 30th May 2007, 10:09 am

Hi Peter,
I am quite fascinated by projection sets as they represent a short lived blind avenue of TV development.
The Decca 1000 uses an off the shelf optical unit (the same as any other projection set using the MW6-2), an off the shelf Mullard EHT genarator (using those nasty Philips tar caps) and Plessy Chassis components.
I don't think there will be any need to operate the tube out of the optical unit.

Anyway, I wish you luck with this and I would be interested to hear how you get on and to see what the pictures are like.

Cheers
Andy

DoctorWho · 30th May 2007, 8:00 pm

Andy - Good to hear your thoughts about the set. It certainly does seem to be a short lived era of television, although, according to the books, it seems that there were some pre-war projection sets, I'd love to have seen one of those! You're right about the Philips condensers in the EHT unit, they were the first to go!

Now, as for an update. I took out the EHT chassis and replaced all of the condensers, with exception to those in the sealed can of course. As Andy mentioned above these were the dreaded Philips black tar condensers, and so, of course, these were all replaced, as was the small electrolytic condenser which is said to only be in the early models and was indeed in this set.

Next I looked at the power chassis, the original can electrolytics are still present and connected, but newer electrolyitcs have been soldered beneath the chassis in parallel with them so that both old and new condensers are connected. Is it alright like this, or should I disconnect the originals?

The main chassis had pretyy much all of the original wax condensers in place, I replaced all of these with new condensers and also replaced all of the electrolytics except for the 3 cans on one side of the chassis and the surface mounted electrolytic. Is this likely to be alright, or should I replace the remaining electrolytics as well? One resistor was physically damaged and had to be replaced and the frame hold potentiometer had breaks in the track and had to be replaced. It was hard to identify the value of the original, it looked like 2K, and this is what I replaced it with, is this right?

The set was powered up, initially there were problems with inability to lock the frame, this was found to be due to the contrast control being set too low, with this increased everything locked fine. The set can now be stood in front of a closed door and a good picture obtained with good sound.

One thing I did notice was a slight blue glow from the EL38. Is this normal, or is this a problem? Aside from this the only other problem is the very occasional loss of frame lock, the controls need a bit of twiddling and then it all settles down. Any ideas what is likely to cause this?

The bottom line is, do I need to replace any of the original main electrolytic condensers mentioned above, is the Frame Hold control the correct value (2K) and does the EL38 with the slight blue glow need replacing, or is this alright?

Now I just need to find some kind of screen to project a decent picture on to. Is it advisable to try and obtain a spare CRT for this set? Currently the picture is very good indeed, but I am not sure how long a life they have.

All in all things have turned out very well, it's a really nice set, very interesting and a cracking picture, which is great. Now I just have to find somewhere to put it!

Any advice on anything I ought to do would be welcome. Thanks again for the help and advice above.

All the best,

Peter.

Tazman1966 · 30th May 2007, 10:07 pm

Excellent news Peter.

For safety's sake I would be tempted to disconnect the old electrolytic caps. By all means leave them in place for visual effect though.

All the best,

beery · 31st May 2007, 10:56 am

Hi Peter,
wow, that was quick.
Yeah the tubes do tend to have a short life, so it is good that your set has a good one.
I'll look up the data when I get home and see what value the fame hold control should be.

Loss of frame lock. Well if the new control is of the right value then you should be able to find lock somewhere in the middile with one end of the control making it roll one way and the other end of the control making it roll the other way. If the frame hold is one-ended then the value may be wrong or other resistor values in the fram stage.
If however the frame hold has a good range, but the picture jumps and roll occasionally then turn your attention to resistor values at the sync separator stage.

As for what happens to the set as it warms up, well it is hard to tell from here. Maybe you need to see what the HT rail does as the set warms up. I agree with Taz about disconecting the old electrolytics. If the old electrolytics were faulty in the past they mave have become low in value (and so new caps were put in parallel), but they may also have become resitivley leaky and this could cause the HT to vary quite a bit.

A glowing EL38 valve is quite normal. The EL38 is the 6.3V version of the PL38 and they always seem to glow.

Cheers
Andy

DoctorWho · 31st May 2007, 10:13 pm

Tas & Andy,

Thanks for the further advice. I'll disconnect those original electrolytics ASAP, I did think that was probably the best way to go, but I prefereed to get the advice of others here with greater knowledge than myself. I'll also try and obtain a spare CRT, I suspected that the probably have a relatively short life.

I'd be grateful to know the corredt value of the frame hold control, it was very hard to read the original print on the old control which was falling apart anyway.

I'll get on to those old electrolytics and then see how things stand. I found a screen on eBay and whilst not the original type, it shoukd make for a much better surface that the front room door!

Thanks for confirming about the EL38, I did hope this was the case.

Thanks again for the help. I'll take some pictures when it's completed and I have the screen.

Peter.

Steve_P · 31st May 2007, 10:40 pm

There are three pots in the frame stages.

1 at 100k, 2 at 1M.

I suspect yours is the 100k one, looking at the circuit.

Cheers,

Steve P

DoctorWho · 1st Jun 2007, 9:55 pm

Thanks for the info Steve, the original was wire-wound, so am I right to assue that this is likely to be the 100k pot? If so, where can you get 100k wire-wound pots now? The original was only connected at one end with the other end not connected to anything if this helps further identify it?

I had some time to-day and replaced all of the remaining electrolyitcs, both in the main chassis and the power chassis and the result is amazing, a little rolling when warming up, but, once warmed up, a very stable and clear picture without any line or frame slip. There were 3 double can electrolytics in the main chassis, these were all 16-16uf condensers, the replacement of these gave remarkable improvement. I followed John (HeaterCathodeShort's) advice on powering up between each condenser change and this was extremely helpful as you could clearly seen the improvement each time one was replaced. Similarly with the electrolytics in the power chassis there was also a noticable improvement. This just goes to show how important it is to change all except for the mica condensers if you want a reliable set that you can use without having to worry.

Thanks again for the advice, any further clarification regarding the frame hold control would be appreciated.

Peter.

Heatercathodeshort · 2nd Jun 2007, 8:40 pm

Hello Peter,
The Decca 1000 was built for Decca by the Plessey company and uses the standard optical unit produced by Philips. The MW6-2 has a fair life and the screen tends to wear out before the tube has the chance to lose emission.

Examination of the screen out of the optical box may show a light brown rectangle where the picture appears. It will still give a reasonable picture under these conditions. The results when working well are similar to the old 9.5mm Pathe home cine projector. Total darkness is required for viewing to ensure a good result. The optical box will protect you from any X ray hazard but in practice the EHt regulation is so poor that rarely more than around 18-20kv will be supplied to the tube under working conditions.

A line or frame collapse will produce a burn line in a split second. Engineers used to substitute a marked tube while testing. Setting up the optical box is a bit like converging a first generation colour set! Focus is in two parts, mechanical and electrical.
Engineers hated these horrors but fortunately most of them were installed in hotels and public viewing areas such as pubs and public halls.
Just as well it was a limited market....Regards John.

DoctorWho · 2nd Jun 2007, 10:23 pm

Thanks for the insight in to this set John. I have to say that it's quite am impressive design. I really would love to find the Decca 121 (I think that's the number) with the screen built in the set, but until such time as one turns up then this is nice to have.

Examining the picture on the CRT with the brightness down low shows a good clear and bright picture, no signs of brown/burning etc. I can imagine that the focussing would be a bit of a nightmare, I'll leave well alone there I think and just use the rear electronic control.

I wonder how many of these sets were sold for domestic use? I suspect this would have been to people with large homes. Any ideas of the original costs as compared to a regular set of the era?

The line whistle is quite unique, hard to describe, but different to the usual line whistle heard on 405 sets, presumably due to the unusual EHT unit? What a bizarre idea to house the EY51's and the condensers in a sealed can, I dread to think what you do if one fails, as EY51's do tend to do.

Thanks again for the input, as soon as I receive the projector screen I have purchased I look forward to watching the set as closely as possible to the method originally intended.

All the best,

Peter.

Heatercathodeshort · 3rd Jun 2007, 9:26 pm

Hello again Peter,
The EY51s used in the projection EHT unit are not the usual ones that you find mounted outside line transformers. They are special very high quality types much smaller versions of the type so familiar to us. They very rarely fail and the whole assembly is sloshing about in oil to maintain insulation. Imagine what it would have been like to have an open EHt unit developing 25Kv in 1951! Fires and shocks I fear...It was bad enough with 6kv!
I know how you love to replace capacitors but my advice is to leave the tin opener in the kitchen drawer...

The strange 'whine' that you hear soon after switch on is the eht oscillator. I think its around 2kcs but I might be a bit out and its only a guess. The line timebase is quiet on these models due to it only having to supply scanning current. The scan coils are well screened and are silent.

You set the focus with the electrical control while observing the picture through the optical box. The set is then moved towards or closer to the screen for final sharpness. If the optical focus mechanical adjustments are out the screen will be unevenly focused. Due to the 'throw' angle from the screen to the optical box the picture shape has to be distorted electrically in the receiver rather like pincushion correction in early colour sets. If I remember its done with an extra EL38.

Mine works well for its day and was one of the better projection sets. Had reliable EHt regulation been possible they would have been very satisfactory. The little square tin was hardly up to the job.

Regards John.

DoctorWho · 4th Jun 2007, 12:38 pm

Thanks for explaining John, I have no intention of opening up the EHT unit, I was just curious as to how the EY51's could survive like this. I had no idea that such high reliability versions were made. Were these versions of the EY51 ever made available for use on other sets?

Thanks for explaining about the unusual whine, I guessed it was related to the method of EHT generation, but I didn't know exactly what it was. It certainly is an elaborate focussing arrangement.

Are these sets suitable for using for a while, or should they only be used for short periods of time? I only ask this in response to your comments about the EHT unit not being terribly reliable.

Thanks for the advice.

Peter.

29th May 2007, 6:56 pm	#1
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Decca 1000 Projection TV Pre-restoration Advice Request. I have recently been given a Decca 1000 Projection TV set which is in pretty good condition. The set looks complete and the only modification I can see is the addition of a 12-channel turret tuner, probably in the mid 1950's. I just wanted to ask if there are any special tips anyone can give me for restoring these sets as I have not worked on one of these sets before? I see that the EHT unit generates 25kv, do the EHT condensers have to be replaced in this unit? If so, which ones? I have found the electronic focus control, but not the manual focus control. I see that there are two large knobs around the projection lens, are these for focus or for positioning of the picture? I'd be grateful of an explanation as to how you manually focus the picture on these sets if possible please. Anything else in particular I should be looking out for with this set? What's the best way to remove the various chassis and what's the best way to test the set? Any advice appreciated. Peter.

29th May 2007, 7:11 pm	#2
tvden Retired Dormant Member Join Date: Oct 2003 Location: Halesworth, Suffolk, UK. Posts: 413	Re: Decca 1000 Projection TV Pre-restoration Advice Request. This set should not be operated out of its box, as it produces X-Rays.

29th May 2007, 7:21 pm	#3
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Thanks for the warning Den, what part of the circuitry produces the X-rays?

29th May 2007, 7:36 pm	#4
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Only the CRT produces X-rays. Enough to be harmful at close range.

29th May 2007, 8:00 pm	#5
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Decca 1000 Projection TV Pre-restoration Advice Request. The EHT in these sets is 25kV but it's from an RF unit so it's not particularly dangerous as there's not a lot of current available. Even 2kV from a mains transformer is a lot nastier. As with any high voltage I still wouldn't recommend touching it on purpose.

29th May 2007, 9:17 pm	#6
Framer Dave Rest in Peace Join Date: Dec 2006 Location: Near Wrecsam, North Wales Posts: 356	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Hello Peter, The EHT condensers (and the 3 EY51s in the tripler) are within an oil-filled can. This is sealed and would be difficult to work on. They do seem to have a good survival rate though and are usually working OK. Trader Service Sheet 1119 covers the EHT unit and 1118 the optical parts, including CRT replacement. Based on personal experience, I wouldn't twiddle any knobs before reading the above! An interesting set. Best of luck with the restoration. Regards, Dave

29th May 2007, 10:17 pm	#7
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Jeffrey - Thanks for clarifying, does this also include the optical lens at the front, or simply the area around the CRT inside the set? Den - Having looked at the various chassis within the set I don't think I will need to remove the CRT, so that's great. I presume inside the set there's little danger outside or from the front or back? Jeffrey - Thanks for explaining about the RF EHT. I will avoid touching it though! Dave - Thanks for explaining about the EHT condensers and the three EY51's, from what you have said am I right to presume that you can't change the EY51's if they are in a sealed oil filled can? Presumably PCB oil? I hope the EY51's are good then. I'll leave this can assembly well alone I think! Thanks for letting me know which service data sheets to work from. I will certainly read the above before starting work on the set. Anyone know how to manually adjust the focus if it is outside the range of the electronic focus control? This is the one thing I haven't yet worked out? A comment has been made that this looks like an elaborate tea trolley, certainly it is most unusual with the drop down flap. I'll report back how the restoration goes. Thanks again for the advice. Peter.

29th May 2007, 11:06 pm	#8
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Decca 1000 Projection TV Pre-restoration Advice Request. If the frame output goes, then the tube will (hopefully) be turned off. This is because the Single White Line would literally burn itself into the tube. Disable the EHT at first plug in. Having a quick look at the circuit, I would try disconnecting the HT to the EHT Unit - Pin 5 on the 'A' Plug. If you want the circuit, it's on Duke Nukem's CD-ROM, available at his site: http://www.thevalvepage.com/servdata/servdata.htm Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

30th May 2007, 8:30 am	#9
Duke_Nukem Octode Join Date: Jan 2003 Location: Birmingham, West Midlands, UK. Posts: 1,268	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Full details of the optical unit here (shameless plug):- http://www.thevalvepage.com/teletech...art1/part1.htm Note that it is possible that there might be different versions of the EHT generator. I would echo other comments and disconnect the EHT unit (or at least disable it) as if either timebase fails it could burn the phosphor very quickly indeed. There should be a protection circuit for this but during initial work I certainly wouldn't want to rely on it. TTFN, Jon PS : If needed, I do have a pucka manual somewhere for this set awaiting scanning - it's an awkward pain-in-the-wotsit size which makes scanning awkward, I guess this is why its towards the bottom of the pile.

30th May 2007, 10:09 am	#10
beery Heptode Join Date: Jun 2006 Location: Ware, Hertfordshire, UK. Posts: 988	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Hi Peter, I am quite fascinated by projection sets as they represent a short lived blind avenue of TV development. The Decca 1000 uses an off the shelf optical unit (the same as any other projection set using the MW6-2), an off the shelf Mullard EHT genarator (using those nasty Philips tar caps) and Plessy Chassis components. I don't think there will be any need to operate the tube out of the optical unit. Anyway, I wish you luck with this and I would be interested to hear how you get on and to see what the pictures are like. Cheers Andy

30th May 2007, 8:00 pm	#11
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Andy - Good to hear your thoughts about the set. It certainly does seem to be a short lived era of television, although, according to the books, it seems that there were some pre-war projection sets, I'd love to have seen one of those! You're right about the Philips condensers in the EHT unit, they were the first to go! Now, as for an update. I took out the EHT chassis and replaced all of the condensers, with exception to those in the sealed can of course. As Andy mentioned above these were the dreaded Philips black tar condensers, and so, of course, these were all replaced, as was the small electrolytic condenser which is said to only be in the early models and was indeed in this set. Next I looked at the power chassis, the original can electrolytics are still present and connected, but newer electrolyitcs have been soldered beneath the chassis in parallel with them so that both old and new condensers are connected. Is it alright like this, or should I disconnect the originals? The main chassis had pretyy much all of the original wax condensers in place, I replaced all of these with new condensers and also replaced all of the electrolytics except for the 3 cans on one side of the chassis and the surface mounted electrolytic. Is this likely to be alright, or should I replace the remaining electrolytics as well? One resistor was physically damaged and had to be replaced and the frame hold potentiometer had breaks in the track and had to be replaced. It was hard to identify the value of the original, it looked like 2K, and this is what I replaced it with, is this right? The set was powered up, initially there were problems with inability to lock the frame, this was found to be due to the contrast control being set too low, with this increased everything locked fine. The set can now be stood in front of a closed door and a good picture obtained with good sound. One thing I did notice was a slight blue glow from the EL38. Is this normal, or is this a problem? Aside from this the only other problem is the very occasional loss of frame lock, the controls need a bit of twiddling and then it all settles down. Any ideas what is likely to cause this? The bottom line is, do I need to replace any of the original main electrolytic condensers mentioned above, is the Frame Hold control the correct value (2K) and does the EL38 with the slight blue glow need replacing, or is this alright? Now I just need to find some kind of screen to project a decent picture on to. Is it advisable to try and obtain a spare CRT for this set? Currently the picture is very good indeed, but I am not sure how long a life they have. All in all things have turned out very well, it's a really nice set, very interesting and a cracking picture, which is great. Now I just have to find somewhere to put it! Any advice on anything I ought to do would be welcome. Thanks again for the help and advice above. All the best, Peter.

30th May 2007, 10:07 pm	#12
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Excellent news Peter. For safety's sake I would be tempted to disconnect the old electrolytic caps. By all means leave them in place for visual effect though. All the best, __________________ All the very best, Tas

31st May 2007, 10:56 am	#13
beery Heptode Join Date: Jun 2006 Location: Ware, Hertfordshire, UK. Posts: 988	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Hi Peter, wow, that was quick. Yeah the tubes do tend to have a short life, so it is good that your set has a good one. I'll look up the data when I get home and see what value the fame hold control should be. Loss of frame lock. Well if the new control is of the right value then you should be able to find lock somewhere in the middile with one end of the control making it roll one way and the other end of the control making it roll the other way. If the frame hold is one-ended then the value may be wrong or other resistor values in the fram stage. If however the frame hold has a good range, but the picture jumps and roll occasionally then turn your attention to resistor values at the sync separator stage. As for what happens to the set as it warms up, well it is hard to tell from here. Maybe you need to see what the HT rail does as the set warms up. I agree with Taz about disconecting the old electrolytics. If the old electrolytics were faulty in the past they mave have become low in value (and so new caps were put in parallel), but they may also have become resitivley leaky and this could cause the HT to vary quite a bit. A glowing EL38 valve is quite normal. The EL38 is the 6.3V version of the PL38 and they always seem to glow. Cheers Andy

31st May 2007, 10:13 pm	#14
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Tas & Andy, Thanks for the further advice. I'll disconnect those original electrolytics ASAP, I did think that was probably the best way to go, but I prefereed to get the advice of others here with greater knowledge than myself. I'll also try and obtain a spare CRT, I suspected that the probably have a relatively short life. I'd be grateful to know the corredt value of the frame hold control, it was very hard to read the original print on the old control which was falling apart anyway. I'll get on to those old electrolytics and then see how things stand. I found a screen on eBay and whilst not the original type, it shoukd make for a much better surface that the front room door! Thanks for confirming about the EL38, I did hope this was the case. Thanks again for the help. I'll take some pictures when it's completed and I have the screen. Peter.

31st May 2007, 10:40 pm	#15
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Decca 1000 Projection TV Pre-restoration Advice Request. There are three pots in the frame stages. 1 at 100k, 2 at 1M. I suspect yours is the 100k one, looking at the circuit. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

1st Jun 2007, 9:55 pm	#16
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Thanks for the info Steve, the original was wire-wound, so am I right to assue that this is likely to be the 100k pot? If so, where can you get 100k wire-wound pots now? The original was only connected at one end with the other end not connected to anything if this helps further identify it? I had some time to-day and replaced all of the remaining electrolyitcs, both in the main chassis and the power chassis and the result is amazing, a little rolling when warming up, but, once warmed up, a very stable and clear picture without any line or frame slip. There were 3 double can electrolytics in the main chassis, these were all 16-16uf condensers, the replacement of these gave remarkable improvement. I followed John (HeaterCathodeShort's) advice on powering up between each condenser change and this was extremely helpful as you could clearly seen the improvement each time one was replaced. Similarly with the electrolytics in the power chassis there was also a noticable improvement. This just goes to show how important it is to change all except for the mica condensers if you want a reliable set that you can use without having to worry. Thanks again for the advice, any further clarification regarding the frame hold control would be appreciated. Peter.

2nd Jun 2007, 8:40 pm	#17
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Hello Peter, The Decca 1000 was built for Decca by the Plessey company and uses the standard optical unit produced by Philips. The MW6-2 has a fair life and the screen tends to wear out before the tube has the chance to lose emission. Examination of the screen out of the optical box may show a light brown rectangle where the picture appears. It will still give a reasonable picture under these conditions. The results when working well are similar to the old 9.5mm Pathe home cine projector. Total darkness is required for viewing to ensure a good result. The optical box will protect you from any X ray hazard but in practice the EHt regulation is so poor that rarely more than around 18-20kv will be supplied to the tube under working conditions. A line or frame collapse will produce a burn line in a split second. Engineers used to substitute a marked tube while testing. Setting up the optical box is a bit like converging a first generation colour set! Focus is in two parts, mechanical and electrical. Engineers hated these horrors but fortunately most of them were installed in hotels and public viewing areas such as pubs and public halls. Just as well it was a limited market....Regards John.

2nd Jun 2007, 10:23 pm	#18
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Thanks for the insight in to this set John. I have to say that it's quite am impressive design. I really would love to find the Decca 121 (I think that's the number) with the screen built in the set, but until such time as one turns up then this is nice to have. Examining the picture on the CRT with the brightness down low shows a good clear and bright picture, no signs of brown/burning etc. I can imagine that the focussing would be a bit of a nightmare, I'll leave well alone there I think and just use the rear electronic control. I wonder how many of these sets were sold for domestic use? I suspect this would have been to people with large homes. Any ideas of the original costs as compared to a regular set of the era? The line whistle is quite unique, hard to describe, but different to the usual line whistle heard on 405 sets, presumably due to the unusual EHT unit? What a bizarre idea to house the EY51's and the condensers in a sealed can, I dread to think what you do if one fails, as EY51's do tend to do. Thanks again for the input, as soon as I receive the projector screen I have purchased I look forward to watching the set as closely as possible to the method originally intended. All the best, Peter.

3rd Jun 2007, 9:26 pm	#19
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Hello again Peter, The EY51s used in the projection EHT unit are not the usual ones that you find mounted outside line transformers. They are special very high quality types much smaller versions of the type so familiar to us. They very rarely fail and the whole assembly is sloshing about in oil to maintain insulation. Imagine what it would have been like to have an open EHt unit developing 25Kv in 1951! Fires and shocks I fear...It was bad enough with 6kv! I know how you love to replace capacitors but my advice is to leave the tin opener in the kitchen drawer... The strange 'whine' that you hear soon after switch on is the eht oscillator. I think its around 2kcs but I might be a bit out and its only a guess. The line timebase is quiet on these models due to it only having to supply scanning current. The scan coils are well screened and are silent. You set the focus with the electrical control while observing the picture through the optical box. The set is then moved towards or closer to the screen for final sharpness. If the optical focus mechanical adjustments are out the screen will be unevenly focused. Due to the 'throw' angle from the screen to the optical box the picture shape has to be distorted electrically in the receiver rather like pincushion correction in early colour sets. If I remember its done with an extra EL38. Mine works well for its day and was one of the better projection sets. Had reliable EHt regulation been possible they would have been very satisfactory. The little square tin was hardly up to the job. Regards John. Last edited by Mike Phelan; 13th May 2008 at 8:55 am. Reason: Edited typos

4th Jun 2007, 12:38 pm	#20
DoctorWho Rest in Peace Join Date: Apr 2005 Location: Devon Posts: 850	Re: Decca 1000 Projection TV Pre-restoration Advice Request. Thanks for explaining John, I have no intention of opening up the EHT unit, I was just curious as to how the EY51's could survive like this. I had no idea that such high reliability versions were made. Were these versions of the EY51 ever made available for use on other sets? Thanks for explaining about the unusual whine, I guessed it was related to the method of EHT generation, but I didn't know exactly what it was. It certainly is an elaborate focussing arrangement. Are these sets suitable for using for a while, or should they only be used for short periods of time? I only ask this in response to your comments about the EHT unit not being terribly reliable. Thanks for the advice. Peter.