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Old 18th Jun 2017, 10:53 am   #21
1100 man
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Default Re: Nearly a Sobell 1000 DST!!

Many thanks for the explanation of the model numbers and for the picture of the model number sticker. You would have thought as they went to the effort of riveting a plate with the serial number on, they would have put the model no. on the same plate! Have looked at my set and can't see any evidence on the back cover or LOPT screen of where a label might have been.

Ours must have been a 1000DS as it didn't have a tuner fitted. I remember it went away to be 'converted' for BBC2. I would have been about 4 or 5 at the time I remember being fascinated by the fact that if I clunked the VHF tuner round, (when mum was out of the room!) at one position things 'changed'- the TV sounded different and the screen changed. At the time I had no idea why this was!!

Cheers Nick
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Old 18th Jun 2017, 11:08 am   #22
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Default Re: Nearly a Sobell 1000 DST!!

A close relative to the Sobell 1000 series. The attachment shows the Masteradio D500DS(T). Note the system switch on the side of the cabinet. The much improved 1000 series actuated this switch from the channel selector.
The D500 employs the dreadful Cyldon PC80 push button tuner.

DFWB.
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Old 18th Jun 2017, 1:29 pm   #23
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by 1100 man View Post
Ours must have been a 1000DS as it didn't have a tuner fitted. I remember it went away to be 'converted' for BBC2. I would have been about 4 or 5 at the time I remember being fascinated by the fact that if I clunked the VHF tuner round, (when mum was out of the room!) at one position things 'changed'- the TV sounded different and the screen changed. At the time I had no idea why this was!!
That's how a lot of us caught the bug. It lasts a lifetime!
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Old 19th Jun 2017, 7:46 am   #24
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by 1100 man View Post

Have looked at my set and can't see any evidence on the back cover or LOPT screen of where a label might have been.

Cheers Nick
This photo shows where the back cover model and brand label should be (adhesive residue).
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Old 19th Jun 2017, 9:01 am   #25
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by Focus Diode View Post
That's how a lot of us caught the bug. It lasts a lifetime!
I noticed this when I was a kid with our first BBC2 set which was the later GEC dual standard chassis with the 5 way turrent tuner for VHF and the rotary tuner for UHF. When clunking the VHF tuner around to UHF the picture and sound on BBC2 was so noticeably different to BBC1 and ITA which were still on VHF 405 only. This was certainly one of the reasons why I caught the bug.
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Old 19th Jun 2017, 9:30 am   #26
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Default Re: Nearly a Sobell 1000 DST!!

What a Fantastic looking set!

It looks like it will scrub up well. Good luck ☺️

Jan
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Old 19th Jun 2017, 9:57 am   #27
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Default Re: Nearly a Sobell 1000 DST!!

Thanks for the back cover picture. Rather than the moulded 'Fibreform' type back, my one is made of flat 'millboard' with the corners folded up and riveted. The bulge for the CRT is a separate pot. The printing for the mains tappings and warning notices is in gold. Still can't see any evidence of where the label might have been!
I've got an hour free, so I'm just about to start cleaning out some of the rather pungent dust and removing the chassis for further investigation- always an exciting time
Cheers
Nick
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Old 19th Jun 2017, 10:38 am   #28
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by 1100 man View Post
Thanks for the back cover picture. Rather than the moulded 'Fibreform' type back, my one is made of flat 'millboard' with the corners folded up and riveted. The bulge for the CRT is a separate pot. The printing for the mains tappings and warning notices is in gold.
Cheers
Nick
Yes, two types of back were fitted to these sets during the course of production.

Something you ought to check when you start work on this set is the condition of the screened lead that connects the frame output valve's pentode anode to the Frame Output Transformer (FOPT) and to frame output stage's HT supply. Photo (rather out of focus) attached, showing the FOPT end.

The inner conductor has a sheath of natural rubber (usually black in colour) and the end near the valve gets rather warm. The insulation of the inner conductor becomes brittle and crumbly, which could lead to a short between inner and screen. I always cut the "dodgy" end back a bit and re-terminate the cable into the two pin plug.

If the LOPT is the type originally fitted (cream coloured solid insulation of the EHT overwind), it will probably be u/s (I know from bitter experience), especially if it is cracked, allowing moisture in. If it's the later black or translucent outer insulation type of LOPT, it may well be OK.
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Old 19th Jun 2017, 12:20 pm   #29
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Default Re: Nearly a Sobell 1000 DST!!

dazzlevision may well correct me, but I suspect that the edited picture may show how your back cover originally looked.
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Old 19th Jun 2017, 12:26 pm   #30
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by volte-face View Post
dazzlevision may well correct me, but I suspect that the edited picture may show how your back cover originally looked.
VF, you are "spot on" (forgive the pun!).

The label would be fixed between the two gold dots, as shown in your edited photo.
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Old 19th Jun 2017, 4:46 pm   #31
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by dazzlevision View Post

If the LOPT is the type originally fitted (cream coloured solid insulation of the EHT overwind), it will probably be u/s (I know from bitter experience), especially if it is cracked, allowing moisture in. If it's the later black or translucent outer insulation type of LOPT, it may well be OK.
Thank you for the prophecy of doom, Dazzlevision My LOPT does have cream coloured plastic insulation for the overwind and yes it is cracked- I felt that wasn't a good sign myself
I'll give it a 'ringing' test as I have done my other LOPT's and see what the results are. If it seems reasonable, I will try the 'passing current to dry it out' method and see if that might prevent it going short.
I won't hold out too much hope though!!
Thanks for the info about the screened lead. I found the other end on the frame timebase board this morning and it didn't look too well!
I like the edited rear cover picture- I'm tempted to look at my rear cover tonight to see if the label has re-appeared!!
Cheers
Nick
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Old 21st Jun 2017, 11:54 pm   #32
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Default Re: Nearly a Sobell 1000 DST!!

Good evening,
So the strip down has begun!! I find the easiest way to clean/ examine and replace components is to dismantle the set into manageable chunks.
The two main PCB's at the bottom are mainly on plugs/ sockets apart from a few soldered connections to the LOPT and line scan panel so it was fairly easy to remove. It was then given a good washing Well a dry brushing only got rid of some of the dust, the rest was very well stuck on. I worked on the basis that I would change any cracked caps and dodgy resistors anyway so what real harm would it do. At least I have a nice clean board to work on now!
Those red Hunts caps look so innocent, I am very tempted to leave them be for the time being along with the ' mustards' and supamolds! I don't doubt some (or all) will end up being replaced though.

The main chassis with all the wiring was given the same treatment and left to dry in the sun. It has all cleaned up very nicely and looks almost new!
The cabinet front has also cleaned up very well and the high gloss sides and top will benefit from a light sanding with 1200 grade paper and then a machine polish with car body compound. There are a couple of small bits of damage on the top which I can make less obvious.
The plastic crt cover is still nice and clear but does have quite a few quite deep scratches and scuff marks. I will sand these down with 400 and then finer wet & dry and finally polish with car body compound.
I removed the LOPT for testing and it is dated April 1965 so must be the original. Hmm..
Very surprisingly, the plastic on the inside of the scan coils has gone all crumbly and is falling apart. Not sure what I am going to do about that.
So all in all I think it can be turned into a nice tidy set and should be a quicker project than my poor old Pilot which I am still plugging away at when I can.
All the best
Nick
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Old 22nd Jun 2017, 12:16 am   #33
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Default Re: Nearly a Sobell 1000 DST!!

I would strongly recommend replacing the red with white lettering Hunts capacitors from experience. They usually look OK and may have worked well when the set was new but after 50 years....
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Old 22nd Jun 2017, 10:14 am   #34
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Default Re: Nearly a Sobell 1000 DST!!

Agreed, but I'd leave the mustards as they both look nice and are very likely to work. However that red and black electrolytic at the rear....
Glyn
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Old 22nd Jun 2017, 10:42 am   #35
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Default Re: Nearly a Sobell 1000 DST!!

Yes, that's on the hit list- it's very nearly cracked in half!! There is a similar one behind the two linearity pots on the frame board. Those red Hunts look so nice though- might leave them for the moment just to see. At least they are fairly easy to get at once the chassis is back together. I will change all 5 caps on the line TB panel under the LOPT as this really isn't easy to get at later!
I imagine all these plastic encapsulated caps were a big step forward in reliability from the wax era of caps.
I know it would make sense to change all the caps (over 1000pf) in the set, but I didn't really want to do a ' blanket 'change. We will just have to wait and see how good they are!
All the best
Nick
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Old 22nd Jun 2017, 3:03 pm   #36
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Default Re: Nearly a Sobell 1000 DST!!

Hello,

Having restored a few of these sets now, I can virtually guarantee that all the red resin dipped Hunts capacitors will be very leaky, as will the yellow TCC Supamold and Duomold types, plus the grey (and some blue) Dubilier types.

The two red/black Plessey electrolytics should be replaced and I would also test the cathode bias resistor for the PCL85/805's pentode section (330 Ohm), as it will almost certainly have gone out of tolerance.

Whilst you are at it, the 2.7M Ohm resistor that connects to the contrast control's slider is a stock fault, as is the 1.2M that feeds Boost HT to the frame oscillator (it's on the small PCB underneath the LOPT "cage"). Whilst you have that tilted out, I'd also check all the high value resistors in the width stabilisation (a.k.a. "set boost") circuitry. They are bound to be out of spec.

It'll save you a lot of time in the long run and they will be much easier to get at and change with the set dismantled!

Last edited by dazzlevision; 22nd Jun 2017 at 3:08 pm. Reason: Added text.
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Old 23rd Jun 2017, 12:28 am   #37
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Default Re: Nearly a Sobell 1000 DST!!

Quote:
Originally Posted by dazzlevision View Post
Having restored a few of these sets now, I can virtually guarantee that all the red resin dipped Hunts capacitors will be very leaky, as will the yellow TCC Supamold and Duomold types, plus the grey (and some blue) Dubilier types.
What a shame: they all look so pretty too But I know you are right, so I will change them anyway as there isn't that many and only a few duomolds and supamolds. I was going to change them all on the line scan PCB anyway as access later will be a pain.
I will check all the high value resistors as a matter of course and the other items you mention.
Many thanks for your input on this: its very useful as you are obviously very familiar with these sets
Cheers
Nick
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Old 23rd Jun 2017, 1:04 am   #38
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Default Re: Nearly a Sobell 1000 DST!!

Those printed circuit resistors with the end caps, the cap can split and be intermittent, easily seen if you check them, may save some problems.
Frank
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Old 23rd Jun 2017, 7:30 am   #39
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Default Re: Nearly a Sobell 1000 DST!!

Hello,

Just to add to your list of components to change:

Sometimes, I like to run my TVs with a weak RF signal, to simulate "fringe" area reception (and to check their sensitivity, stability and, where incorporated, the flywheel line sync operation).

A common problem in valve VHF tuners is the mixer pentode's g2 (screen grid) feed resistor going o/c or high in value, which causes low gain. Worth checking this in your set.


On the small PCB under the LOPT "can", there are two non-standard value "S correction" capacitors (usually TCC yellow cased axial types). IIRC, the values are 0.11uF and 0.16uF. You can use standard values (0.1 and 0.15uF), but the horizontal linearity may not then be as good as it could be. I either select on test to get as close as possible, or use two (value measured) Cs in parallel (i.e. 0.1 and 0.01 = 0.011uF).
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Old 30th Jun 2017, 12:33 am   #40
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Default Re: Nearly a Sobell 1000 DST!!

Good evening,
So not particularly encouraging news on the GEC front. I've been doing various tests now I'm back on terra- firma.
I hooked the tube up to the B&K CRT tester and the emission was, well pretty much non existant The needle on the meter barely climbed off the zero. I left it on excess heater volts for a while but no change so I gave it a gentle 'clean' and the needle at least climbed into the 'bad' area! So I gave it a proper rejuvinate- twice. The best I can get out of it is the needle is just on the lower edge of the green 'good ' area of the meter. Run from 8Volts, I get what I would consider an acceptable emission reading. So I don't have high expectations of a great picture- and it's a Mullard tube too!

I then gave the LOPT a 'ring' test in the same way as I had done with several others. The trace on the 'scope' decayed to nothing after about 1/3 of the period indicating undoubtedly shorted turns on the overwind Thanks Dazzlevision for predicting that gloomy outcome!

I next turned my attention to the various capacitors on the PCB's. As they were all nice cheerful colours (red Hunts, yellow TCC Supamolds, Mustard, mustards and blue Dubilliers) I couldn't believe they would all be faulty- after all there were no wax ones in sight!!
I lifted a leg of all the caps over 1000pf which the GEC double sided print made very easy from the top side of the board. I then tested each cap with a digital 'megger' set to 250V.
The results were exactly what various people had predicted. All the red Hunts were about 5Meg and the Dubilliers and Supamolds weren't much better. All the mustards were over 200 meg so are probably ok and are at least worth measuring the capacitance. One was dead short but then it did have a crack in it's coating. So nearly all the caps will have to be replaced.

All the resistors are the 'carbon rod with crimped on ends' type designed for pcb mounting and I worked my way through the circuit measuring each one. Pretty much all of them were exactly 20 % high so 47K read 57K, 100k read 120K, 470K read 570K etc. Strangely the 3k3 PFL200 screen resistor was spot on and looked original!!
It remains to be seen how well the circuit works with such out of tolerance resistors as I'm not going to replace the whole lot
So a bit of a recap is in order now and I'll worry about the LOPT and CRT when I get to the point of powering it up.
That's it for now
All the best
Nick

Last edited by 1100 man; 30th Jun 2017 at 12:41 am. Reason: Extra text added
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