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 Feb 2020, 9:20 am   #21
Vectamart
Pentode
 
Vectamart's Avatar
 
Join Date: Feb 2007
Location: Ventnor, Isle of Wight, UK.
Posts: 141
Default Re: Sobell 1000 DST at long last!!

It would be good to have another catch-up, Nick.
Vectamart is offline  
Old 13th Feb 2020, 12:14 am   #22
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

This chassis uses two electrolytic cans- one 200 + 200 mfd as the main reservoir & smoother, and one 100 + 50 mfd as further smoothing for the HT line to the signals stages & frame output. Both good old Hunts capacitors!

The 200/200 has been replaced at some point by an RS branded 100/200 mfd dated 1973.

My method for reforming/ checking capacitors is to strap both sections together and connect them via an AVO 8 to a variac and bridge rectifier. The voltage can then be brought up gradually and the current monitored on the AVO.

I consider a capacitor acceptably reformed if the leakage current at the full ( usually 275V) voltage is less than 1ma. Preferably 0.5ma.

The 100/200 RS replacement responded fairly quickly, but the Hunts 100/50 took considerably longer. However, both managed to achieve a leakage of about 0.3ma at full voltage with both sections of the cap strapped together which I was very happy with.

As the 100/200 RS cap is in good order and a period repair, it can stay in place, the missing 100mfd can be taken care of with a small electrolytic hidden behind the chassis rail. This will be unseen when the chassis is in the cabinet.

And so to the LOPT with it's cracked potting on the overwind and open circuit coil under the overwind.

As I had hoped, the lead out wire had suffered 'green spot' and had parted company within the sleeving , leaving enough to attach a new wire to.

Before dismantling the transformer, I did a 'ring test' on my makeshift LOPT tester which indicated that the transformer was fine at least from the point of view of shorted turns. For some reason, the clamp bolts and core were loose, so taking the transformer to bits was rather too easy!

With the overwind assembly removed, repairs are much easier. After a clean up with some IPA to remove the crud, it's been cooking on the power supply for a few days. 140ma at 21V yields 3W (ONO) of heat which keeps it warm enough to drive out any moisture.

I'll then give it several coats of transformer varnish to hopefully seal it and stop more moisture getting in.

The photo shows the overwind cooking nicely sitting on top of the AVO- there is nothing to beat an analogue meter for this purpose! You can also just see the very fine wires leading to the winding under the overwind.

Hopefully, all this messing about will ensure the LOPT is functional and does not suffer premature failure, although I don't doubt it will run much hotter than I would like and will need fan cooling like nearly all my other sets!

All the best
Nick
Attached Thumbnails
Click image for larger version

Name:	DSCN0915.jpg
Views:	197
Size:	88.5 KB
ID:	198901  
1100 man is online now  
Old 18th Feb 2020, 12:10 am   #23
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

Time for a little scan coil surgery whilst waiting for some other components to arrive.

I've never stripped down a set of scan coils before: I've never needed to- they are not something I've ever had any problems with before. Until now!

The first thing that was apparent was that the clamp band had fractured and the two ferrite formers had a gap between them. Like my GEC version of this set, the plastic that the coil assembly is made from had gone very crumbly. Very much like the Ekco line output transformer shrouds that disintegrate.

I don't doubt they would have worked fine but as I found on the GEC, every time they were adjusted or touched in any way, they fell apart a bit more and dropped a pile of crumbly plastic onto the chassis.

Some years ago at Harpenden, right at the end of the bring & buy, Beamcurrent Brian thrust a box containing a load of Baird 620 parts into my hand in exchange for a pound. There were several brand new sets of scan coils which on the face of it looked pretty much the same as the Sobell ones. They were obviously meant for the same type of 110 degree tube and actually probably would have worked just fine as they were.

My plan is to use one of the Baird 620 coil formers and transplant the coils from the Sobell onto it.

I was also intrigued as to how the things were assembled as it was hard to work out how to take them apart.

I've just stripped down the sobell ones and you can see that there is not much left of the plastic former- just a pile of dust!

I now need to do the same with one of the Baird ones and see if I can transplant all the bits.

All the best
Nick
Attached Thumbnails
Click image for larger version

Name:	DSCN0916.jpg
Views:	181
Size:	90.7 KB
ID:	199212   Click image for larger version

Name:	DSCN0918.jpg
Views:	181
Size:	142.3 KB
ID:	199213   Click image for larger version

Name:	DSCN0919.jpg
Views:	180
Size:	115.3 KB
ID:	199214   Click image for larger version

Name:	DSCN0920.jpg
Views:	179
Size:	118.0 KB
ID:	199215   Click image for larger version

Name:	DSCN0921.jpg
Views:	189
Size:	113.9 KB
ID:	199216  

1100 man is online now  
Old 20th Feb 2020, 6:38 pm   #24
beery
Heptode
 
beery's Avatar
 
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
Default Re: Sobell 1000 DST at long last!!

Hi Nick,
that's very brave to take apart the scan coils. Do you think that is the same plastic that was used for the collar washers in BRC UHF tuners?

Cheers
Andy
beery is offline  
Old 21st Feb 2020, 1:12 am   #25
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

Quote:
Originally Posted by beery View Post
Hi Nick,
that's very brave to take apart the scan coils. Do you think that is the same plastic that was used for the collar washers in BRC UHF tuners?

Cheers
Andy
Hi Andy,

Brave or foolish:- I'm not sure which yet!! They were in a very poor state and never having taken a set of coils apart before, the temptation was too great to resist!

The former looks to be made of Polythene and has just turned to dust in lots of places. This set is 56 years old and I guess many plastics have not proved to be stable over that length of time- BRC tuner washers & Ekco line O/P shrouds to name but two. Mind you, I've never seen a set of scan coils in this state before, apart from the ones on my GEC version of this set.

I've now stripped down the set of 620 coils which are to provide the plastic former. They are very very similar to the Sobell ones but the profile of the line coils is slightly different. The line coils, which are quite a complex shape, are designed to be an exact fit in the plastic former.

The end result is that the Sobell ones don't quite fit and there is no convenient way to modify the former to accommodate them. The frame coils, mounted on the shaped ferrite sections, fit perfectly.

So my decision, at least as a test, is to use the 620 line coils and the Sobell frame coils. There really doesn't look to be much difference between the 620 & Sobell line coils, just a slight difference in form.

The picture shows the very nice new plastic former and on the left the 620 line coil (1 of 2) in a fetching shade of purple! The Sobell coil is on the right.

So will it work? I suspect it probably will, but we will just have to wait and see!

All the best
Nick
Attached Thumbnails
Click image for larger version

Name:	DSCN0922.jpg
Views:	163
Size:	150.3 KB
ID:	199426  
1100 man is online now  
Old 22nd Feb 2020, 12:25 am   #26
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

The restoration of this set can be split up into a number of tasks, each of which is a project in it's own right. Restoration sounds a bit pretentious- I'm only really doing what I consider necessary to make this a functional & reliable TV.

After all, I can't see much point in powering it up when there are so many obvious faults that are apparent just by a visual examination. Also there is little point in potentially damaging things like the LOPT and smoothing caps when with some prior work they can be saved.

Access to the PCB's on this set is not great so I'd much rather strip everything down and work on individual items in comfort. Replacing capacitors which are going to be leaky (after testing them at working voltage to give them the benefit of the doubt) is much easier at this stage.

Believe me, when it's all put back together, there will still be plenty of proper fault finding to be done with circuit diagram, meter, scope and some head scratching!

The set has been broken down into the following parts each of which is being overhauled separately.

1) Main chassis & metalwork
2) Main chassis components- smoothing cans, mains droppers, transformers etc
3) Line scan PCB mounted under LOPT housing
4) Main PCB's- signals board & line/ frame timebase PCB's
5) Line output transformer
6) Scan coils & CRT
7) UHF tuner
8) VHF tuner & System switch controls
9) Cabinet, implosion screen & knobs

Good progress has been made so far on all of the above and it's nearly time to start putting it together again! That's where things start to get exciting!

All the best
Nick
1100 man is online now  
Old 22nd Feb 2020, 6:08 pm   #27
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: Sobell 1000 DST at long last!!

A number of scan coils used to fall to bits when these receivers were only 5-10 years old. I think the main cause of the problem was the line linearity sleeve being positioned much further into the coil assembly than is necessary causing overheating of the line coils. Nasty things..
That strap when broken causes a really odd 'S' shaped picture, pulsing and rippling.
I have just experienced exactly the same problem with a Sobell 1018. Small World! John.
Heatercathodeshort is offline  
Old 23rd Feb 2020, 12:24 am   #28
The teleman
Pentode
 
The teleman's Avatar
 
Join Date: Dec 2007
Location: County Durham, UK.
Posts: 243
Default Re: Sobell 1000 DST at long last!!

I’ve had the very same problem with all makes of sets
I remember when we used to repair the ITT KB VC200 sets back in the 70’s & 80’s this sort of thing happed a lot and caused the coils to go shorted turns or open circuit
A replacement was the only cure back then
I must admit I have several GEC sets that use this 2000 series chassis and have not seen the problem on any of them as yet
Good luck with the reassemble

Chris
The teleman is offline  
Old 25th Feb 2020, 1:07 am   #29
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

Quote:
Originally Posted by Heatercathodeshort View Post
A number of scan coils used to fall to bits when these receivers were only 5-10 years old. I think the main cause of the problem was the line linearity sleeve being positioned much further into the coil assembly than is necessary causing overheating of the line coils. Nasty things..
That strap when broken causes a really odd 'S' shaped picture, pulsing and rippling.
I have just experienced exactly the same problem with a Sobell 1018. Small World! John.
Hi John & Chris,

I did wonder if it was heat damage, but I feel it's more degradation of the plastic due to chemical changes within it. It's gone exactly like the Ekco line O/P shrouds- yellow and gritty looking and just crumbles to dust when touched. Maybe some batches of plastic were better than others at the time?

Anyway, I've reassembled a set of coils using the 620 former, 620 line coils & Sobell frame coils. I'll just have to see how well it works with slightly different line coils. Out of interest, what tubes were used in the 620 chassis? That would give me some idea of what to expect!

Progress has been made on other aspects of the set too.

Some of the chassis metalwork had suffered from rust & corrosion, so I rubbed these areas down, treated them with rust killer, masked off the rest of the chassis and my friend Jon, the car body painter, has very kindly sprayed them.

As he has done with other chassis of mine, he mixes a colour based on metallic silver with a dash of gold- this ends up a pretty good match to the original plating and I'm very happy with it!

All the suspect caps (that have actually been measured faulty) on the main & scan PCB's have been replaced, as have a few high value resistors in critical places. The system switch has been cleaned & lubricated & now works properly.

The main smoothing electro's have been reformed and an extra 100mfd added discretely round the back of the chassis to make up the 200mfd of one of the cans.

The mains dropper has been repaired by linking out the O/C section & utilising an unused bit that was conveniently the correct value.

The LOPT has been striped down, the bolts & the core were loose anyway for some reason. The overwind was gently heated on the power supply for several days to hopefully drive out any moisture and then coated with several layers of transformer varnish. This should seal up all the cracks in the epoxy coating!

The open circuit winding was luckily just the fine lead out wires having corroded inside the sleeving. It was all rather fiddly putting it all back together again and I don't doubt that won't be the end of the matter! There is bound to be leakage or other issues and it will probably just hiss menacingly at me!

Both UHF & VHF tuners are in the process of being overhauled- the slow drive for the UHF has seized solid & the VHF one needs a good clean- it's contacts are black. Also the roller that makes it go 'clunk, clunk' has fallen apart and needs a cunning repair.

But I'm starting to put things back together. The main PCB's, chassis & LOPT can now be wired back together so it's getting ever closer to getting some power!

Just out of pure interest, I've been looking at the circuit of the Sobell 1018 referred to by John. It looks to be almost identical to the 1000 and has the same valve line up but a totally different chassis design & layout. I wonder why the manufacturers went to the huge effort & expense of retooling to use the same circuit design but with a different chassis? It's difficult to see where the benefit was?

All the best
Nick

Last edited by 1100 man; 25th Feb 2020 at 1:29 am. Reason: more text added
1100 man is online now  
Old 25th Feb 2020, 11:34 am   #30
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: Sobell 1000 DST at long last!!

The 19" tube employed in the Baird 600 series is the Mullard AW47-91, a tube that was fitted by many manufacturers over a number of years. It was a very good tube and it is very rare indeed to discover a faulty one unless over run by a mains dropper bodge.

Most scan coils of the period were low resistance field windings and slightly higher resistance line coils. Many were manufactured by Plessey but Thorn produced their own coils to a very high spec and I have never replaced a single set.

Give them a try. The only exception to the rule is the Philips TG100U series. Early encapsulated coils used to fail [O/C frame] giving the classic bent horizontal line but Philips coils had to be used. Any attempt to fit others resulted in hopeless frame linearity.

The Ekco transformer shrouds were an odd form of plastic material not seen elsewhere. [Ekco had a very noted plastics division] It was only used from 1954 the first model being the T221. Several serious fires were caused by these shrouds due to smoldering that continued after the receivers were turned off at night. It had a sickly sweet smell when decomposing. The actual transformer windings were excellent probably due to the 'dope' [probably of Ekco manufacture] used to impregnate the overwind preventing damp ingress. The earlier Perspex arched shroud gave no problems at all. John.
Heatercathodeshort is offline  
Old 29th Mar 2020, 11:52 am   #31
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

With the current world crisis unfolding, it seems trivial to be writing about old tellys! However, I'll update on progress so far.

I reached the exciting point of applying some power. The tuners had been rebuilt, the LOPT refitted etc. The tuners & controls are on a separate chassis, so this was sat on the bench next to the main chassis and connected up.

Quick check that nothing was touching anything it shouldn't, make sure mains switch was 'on'. Connect meter to 'boost' rail in line output stage. This gives a good indication of what's going on in the line stage. Make sure system switch is in 405 position for the simple reason I can still hear 10Khz (just) which will aid fault finding.

Deep breath. Plug into mains. Erie silence. No valve heaters.

A quick check revealed a white wire that connects the heater supply to the UHF tuner going nowhere...

Plug in again. Valve heaters alight. Wait. No line whistle & no reading on meter.

Even with the line stage not working, once the PY800 efficiency diode starts conducting there should be HT volts on the boost rail. So it was likely the PY800 was faulty. It did look rather pale round the getter.

Fit another PY800. Plug in again. Wait. Healthy line whistle. Boost 750V. EHT rectifier heater lit. Raster on screen. Yippey!!

Feeding in a signal from the Aurora on CH1 showed there was an AGC issue, as when the tuner was set to CH1, the set was totally overloaded and the frame collapsed! Tuning in on CH2 position made things better and quite a good picture was obtained. An issue for another day methinks!

The focus was poor, but the picture was surprisingly good, considering the emission showed as very bad on the tester.

Start to make a few checks on HT rails etc. CRACK, CRACK, FLASH. Picture vanishes. Monumentous humming from isolation transformer. Hastily unplug! B

Its a 2KVA islolation transformer (courtesy of Hammonds!) and sounded as if a dead short was on it's output.

Sure enough, measuring from the PY800 top cap, showed 25 Ohms to ground. All eyes turn to the LOPT as there isn't anything else which could cause a short to ground at this point.

There is a winding on the primary that provides a line pulse to the flywheel sync circuit. One side of this is grounded. I knew nothing good ever came of flywheel sync!!

Stripping down the LOPT and examining the primary showed that this winding is the innermost one. The main winding is then wound on top. Unsurprisingly, a grounded winding immediately below the main winding is asking for trouble and trouble has certainly been provided!

So what to do....

Stay tuned!
1100 man is online now  
Old 30th Mar 2020, 5:58 pm   #32
thermionic
Heptode
 
thermionic's Avatar
 
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 986
Default Re: Sobell 1000 DST at long last!!

Hi Nick.

That’s a blow, after all the hard work! I would isolate that winding and leave it electrically floating. Try winding on about 4 turns of insulated wire around the outside of the LOPT to provide line pulses for the flywheel circuit. Remember you need to get the phasing right, so you may need to reverse the connections!


I’ve been working on my Sobell 1005 DST, today, which I recovered from an empty house a few years ago. It’s now working quite well, but needs a bit of tweaking.

I shall be following your progress with interest!


Cheers.

SimonT.
Attached Thumbnails
Click image for larger version

Name:	9D226E51-4C5D-45E3-B46B-1F98B87B9618.jpg
Views:	162
Size:	94.6 KB
ID:	201834   Click image for larger version

Name:	73524636-687C-44F4-A8B8-EF608F61F85C.jpg
Views:	129
Size:	105.1 KB
ID:	201835   Click image for larger version

Name:	D52A2534-1946-4347-A8DD-306640061462.jpg
Views:	126
Size:	145.6 KB
ID:	201836  
__________________
The honesty of imperfection..........
thermionic is online now  
Old 30th Mar 2020, 6:26 pm   #33
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

Quote:
Originally Posted by thermionic View Post

That’s a blow, after all the hard work! I would isolate that winding and leave it electrically floating. Try winding on about 4 turns of insulated wire around the outside of the LOPT to provide line pulses for the flywheel circuit. Remember you need to get the phasing right, so you may need to reverse the connections!
Hi Simon,
I wasn't really surprised, to be honest. I just expect LOPT's to cause me grief and they almost always do! I'd taken some care to dry out the overwind, hooked up to the power supply and then re- insulated it to avoid problems. I'd not done anything to the primary though.

You are thinking along the same lines as me: and in fact I've done a sort of inside out rewind! I'll write up the details later if I get a chance.

Thanks for posting pictures of your 1005- I've never seen one in the flesh. I still have the original sales leaflet for our family 1000DST purchased in about 1964. It has mum's shorthand scribble noting the price & how much to add the UHF tuner! It shows pictures of both the 1000 & the 1005 in period room settings. The 1005 has a sailing yacht sitting on top!

Strangely, your pile of dead components look exactly the same as mine! I know exactly which resistors those are as they were the only ones I changed!

Out of interest, what state are your scan coils in: have they crumbled to dust yet?

Looks like you have made good progress with yours.

All the best
Nick
1100 man is online now  
Old 30th Mar 2020, 9:28 pm   #34
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

So not for the first time, it's time for some LOPT surgery.

Looking at the primary winding, pictured below, shows that it's wound with fairly thick wire and just looks to be wound in even layers. Apart from the offending winding that feeds the flywheel sync circuit, the rest is one continuous winding with multiple tappings.

My first thought was that I could rewind the whole thing myself and I started dreaming up makeshift coil winders. Obviously, I'd have to count the turns for every layer as I unwound it, but it would be 'doable'.

But a cunning plan was forming...

If my assumption was correct, the first layer of the primary had flashed over to the sync winding immediately below it. Certainly resistance checks seemed to indicate this.

So the idea was to cut away the inner paxolin former & unwind the sync winding from within the primary. This was actually achieved fairly easily, although it was a bit of a fiddle. There was an obviously blackened area as it was unwound and the enamel had become charred. It was a single layer of 50 turns.

Unsurprisingly, the first layer of the primary, where it was in contact with the sync winding had suffered similar damage. This was also unwound in a similar way. Again about 50 turns.

So far so good. Theoretically, all I needed to do was to wind another coil with a single layer of 50 turns and insert it where the old winding had been. The 50 turns for the sync winding would have to be put somewhere else, maybe wound on top of the primary coil.

Not having any new wire, I straightened out the old stuff. There was a lot of bare sections with no enamel and obviously the thing would not work if I ended up with shorted turns.

I made up a former from a bit of clear film held together with Sellotape and wound a rather rough looking coil on it using the old wire. Finished off with another layer of Sellotape. I could only fit 40 turns on, but under a lens I could not see any shorted turns.

Making sure I'd kept the winding direction the same, I inserted my coil into the centre of the primary which was a nice snug fit.

All the multitude of lead out wires were tacked back onto their respective pins and the transformer roughly reassembled for testing.

Obviously there would be no sync, but it would prove whether the idea was viable.

To my pleasant surprise, it worked a treat. With careful adjustment of the line hold, the picture could be made to be almost stationary. There was less width than before, but that was no bad thing as there was a bit too much before. The damaged winding was the bit that fed the scan coils, so with 10 turns less I suppose it would have less width.

As this was only a lash up to prove a point, I didn't take any pictures.

The next part of the plan is to wind a new sync winding on the outside of the primary. The outside is at much higher potential, so insulation will be necessary.

I shall make a proper job of it with some new wire & Kapton tape at some point. In fact, there should be enough room, when I do it properly, to wind a two layer coil that will fit down the centre of the primary. Then the sync winding will be where it should be.

All in all, I was quite pleased with my efforts: its always nice to salvage something that seems on the face of it to be scrap!

Cheers
Nick
Attached Thumbnails
Click image for larger version

Name:	DSCN0925.jpg
Views:	114
Size:	77.2 KB
ID:	201850  
1100 man is online now  
Old 31st Mar 2020, 7:47 pm   #35
Colourstar
Octode
 
Colourstar's Avatar
 
Join Date: Feb 2006
Location: Ilkeston, Derbyshire, UK.
Posts: 1,397
Default Re: Sobell 1000 DST at long last!!

Your a brave chap Nick, well done! A fine example of 'nothing ventured, nothing gained'. I'm following your progress with interest.

Incidentally, Simon's excellent set pictured a few posts up the thread is a model I've never seen before. I wonder if one of its parents was a Bush TV125....!

Anyway keep up the good work.

Steve
Colourstar is offline  
Old 31st Mar 2020, 8:31 pm   #36
thermionic
Heptode
 
thermionic's Avatar
 
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 986
Default Re: Sobell 1000 DST at long last!!

Quote:
Originally Posted by 1100 man View Post
Quote:
Originally Posted by thermionic View Post

Out of interest, what state are your scan coils in: have they crumbled to dust yet?

Looks like you have made good progress with yours.

All the best
Nick

Hi Nick.

Luckily, my scan coils are fine. The plastic is not cracked or crumbling in any way. Maybe sourced from a different supplier?

Unfortunately, my progress has been curtailed due to the LOPT showing signs of trapped dampness. The usual slow dimming of the raster and shrinking width after a period of operation.

I’ve removed the LOPT now and am passing a DC current through the overwind! Incidentally, there was a date stamp on the bottom of the LOPT of 3rd December 1964.

Good luck with your transformer!
__________________
The honesty of imperfection..........
thermionic is online now  
Old 31st Mar 2020, 8:41 pm   #37
thermionic
Heptode
 
thermionic's Avatar
 
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 986
Default Re: Sobell 1000 DST at long last!!

Quote:
Originally Posted by Colourstar View Post

Incidentally, Simon's excellent set pictured a few posts up the thread is a model I've never seen before. I wonder if one of its parents was a Bush TV125

Steve

Hi Steve.

Yes, you do have a valid point there!

This set was hidden in a boarded up cupboard in an empty house I was rewiring a few years ago. It was literally luck that it was discovered. The owner of the property had asked the builder if the door panel could be forced open, as he had hoped to use the apparent recess for shelving. The door panel had been nailed shut and had many layers of filler & paint around the periphery to seal the gaps. It must have been hidden in there for a good few years.

Cheers. SimonT.
__________________
The honesty of imperfection..........
thermionic is online now  
Old 31st Mar 2020, 9:02 pm   #38
Colourstar
Octode
 
Colourstar's Avatar
 
Join Date: Feb 2006
Location: Ilkeston, Derbyshire, UK.
Posts: 1,397
Default Re: Sobell 1000 DST at long last!!

That's an amazing story Simon! What were the odds of the set being discovered all those years later by a tv collector?

I have a GEC BT455 here which is another model using the same early dual standard chassis as your Sobell and Nick's. The 405-line pictures on these sets are truly excellent.

Steve
Attached Thumbnails
Click image for larger version

Name:	BT455.jpg
Views:	110
Size:	75.2 KB
ID:	201933  
Colourstar is offline  
Old 31st Mar 2020, 10:37 pm   #39
1100 man
Octode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 1,377
Default Re: Sobell 1000 DST at long last!!

Quote:
Unfortunately, my progress has been curtailed due to the LOPT showing signs of trapped dampness. The usual slow dimming of the raster and shrinking width after a period of operation.
Ah, that's bad luck! What sort of overwind does your transformer have? Both of mine use a hard beige plastic type of encapsulation which was covered in deep cracks.

The overwind on my GEC transformer (which was dried out & re varnished), works fine but gets too hot after about half an hour. A small 2" cooling fan keeps it cold & it will then work fine for as long as I want. I've had to resort to this technique for several LOPT's- it's a lot cheaper than a rewind! Did someone say 'bodge'?....

Is it overheating that's causing yours to fail after an hour?

Hi Steve,

Does your GEC use this exact chassis or the slightly earlier one? Is your system switch actuated by the VHF tuner or is it manual? The Sobell 1000 uses a PFL200, whereas the earlier chassis uses (I think) a PCL84 for the video amp.

These sets are certainly capable of producing excellent pictures, especially on 405. Of course, as we have so much signal available from UHF modulators, that overcomes the potentially noisy valve UHF tuner. So the 625 pictures are pretty good too.
I love the regulated line & frame timebases. The picture size stays rock steady as the brightness changes!

Thanks for the picture & the comments.

All the best
Nick

Last edited by 1100 man; 31st Mar 2020 at 10:47 pm. Reason: more text
1100 man is online now  
Old 2nd Apr 2020, 9:02 pm   #40
thermionic
Heptode
 
thermionic's Avatar
 
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 986
Default Re: Sobell 1000 DST at long last!!

Hi Nick.

Well, the overwind has had 100mA DC passing through it for the past 48 hours and and then the whole transformer has been left to bake in my ‘slow cooker’.

I’ve fitted some new silicone EHT lead, and sprayed the windings with conformal coating. Tomorrow I’ll refit it and hope for the best!

How’s the progress with your Lopty?

Cheers. SimonT.
Attached Thumbnails
Click image for larger version

Name:	68689E97-6A63-4F68-876C-D8632A1E63C8.jpg
Views:	86
Size:	108.4 KB
ID:	202082  
__________________
The honesty of imperfection..........
thermionic is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:37 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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.