Sobell 23" Dual Standard

[Hybrid tellies]

That is looking really promising. I repaired loads of these back in the day, mostly 19" GEC models, for customers who were keeping them as second sets.

[Tazman1966]

Originally Posted by Welsh Anorak

... my interest soon fell away when I found all the CRTs had been necked...

I suppose they might have been worth a punt as by that time (beginning of the 80s?) both 19" and 23" reguns would be as cheap as chips. Shame they'd been necked though

[Tazman1966]

Originally Posted by MickMcmichael

...A few jobs later and things are looking up...

Indeed they are. Well done on a nice result. Look forward to the final summary.

[sexton_mallard]

That is a lovely set. I love the bezel styling in particular which accentuates the curvy rectangle of the CRT.

[Heatercathodeshort]

Cheers Mick and well done with yours!

I was going to post this as a separate thread but as the two were identical I have chopped it down to include in your posting. Really strange that two quite rare receivers were being worked on at virtually the same time. Tales of the Unexpected!

To cut a long story short it was a similar event to your example! The mains dropper required replacement together with most of the caps in the frame circuit. The shiny red Hunts .01uf were good quality but now leak, not surprising after so many decades.

I feel a bit of a fraud with this one. It dates back to the shop days and was presented to me by a customer after installing a brand new Toshiba C2290B1K in 1981. It has sat around after being wrapped up in commercial film wrap since that date and thought it was about time it was either dumped [I just said that to gain your attention]or repaired.

This series of Dual Standard Sobell produced models covers a huge range of models.
They include GEC and to a limited extent, Masteradio, a company taken over by the GEC group in the 1960's.

They were produced at the Sobell factory based at Slough employing Mullard valves and a Mullard tube.

The model 1023 is a 23" table model employing a Mullard A59-11W 'Panorama' Rimband protected tube. The one fitted to this Sobell is 100% producing a brilliant picture from cold.

Some versions of this chassis are fitted with what is called a 'Fenbridge Cap' Yer I know, it sounds like something dodgy but was simply a tough plastic cover that was stretched over the faceplate [it gets worse] of the CRT and secured with a metal strap. [even more dodgy] The surface of this abomination was covered in a series of tiny pimples that gave the effect of newsprint or 'Spot Wobble' popular with larger screen Ekco receivers of seventeen years previously.

At first glance when removing the back I was presented with a chassis covered with a thick layer of fine dust, just the way I like them. The chassis was released to gain access to the mains filter blue Dubiliar .1uf lurking on a tag board at the front of the chassis member. This was snipped out of circuit and after a quick check over I applied the mains. The valves lit and after less than a minute a bright raster appeared on the screen. It was lacking in height and a quick flick of the tuner proved that the receiver circuits were doing something. Changing the system switch to 625 produced a nice loud hiss and a grainy raster.

It was at this point I switched off and decided to warm up the overwind by way of 60m/a passed through it for a couple of days. The transformer fitted is fortunately the black type. The earlier white plastic ones are nothing like as reliable and tend to crack and split. If you catch them early enough you can often save them from failure by drying them out and resealing the overwind with resin.

As mentioned the mains dropper required replacement as the original had a tacky resistor across one of the H.T. surge limiter sections together with most of the caps in the frame circuit. The shiny red Hunts were good quality but now leak, not surprising after so many decades. I decided to replace all the Dubiliar caps mounted underneath the LOPT. This involved removing the LOPT which is secured by very small circlips. They broke of course but were easily replaced with 6BA nuts after threading the LOPT clamp bolts.

With this completed the chassis gave a bright raster on both 405 and 625. With a UHF signal applied a good picture was received that took only a few minutes to square up on the test card.

Results on VHF were very poor and intermittent due to dirty contacts on the tuner band change switch. This took a lot of dismantling to gain access to the slide bar and switch contacts as can be seen in the pictures. This involved the removal of two internally soldered screens to allow the slide bar to be removed for cleaning and giving access to the tuner contacts. luckily the tuning wands were not seized in the tuning coil formers as they are quite delicate.

With it all put back together it worked faultlessly on VHF/405.

These are very good receivers. The only weak points are the mains dropper, 18K and 5.6K resistors in the EH90 locked oscillator FM detector/AF amp and the difficulty in cleaning the VHF tuner. A really odd effect is created when the phosphor bronze strap holding the Ferrite scan coil yoke together breaks. It produces an S shaped picture vertically through the picture, unmistakable once you have seen it. Just replace it with a cable tie.

The pictures show 1 and 2. The dusty chassis before starting work cleaned with small paintbrush and vacuum cleaner. 3. cleaned. 4 5 6 7 8 9 10 The VHF tuner dismantled. 11 12 13. Off screen pictures that do not do justice to the super bright high contrast pictures produced by the Mullard A59-11W tube. Regards, John.

[Heatercathodeshort]

Some more pics.

[Heatercathodeshort]

The final pics. J.

[Hybrid tellies]

That is looking really good and that tube nice and bright. Seeing these pictures and with your write up brings back many happy memories of working on this chassis. It was on these sets that I learnt all about working with double sided print. Never had to replace a LOPT on these and the only tube failure was on the later 2043 which used the 20" A50-120WR. I cannot remember if it was a Mullard or Mazda

[1100 man]

It's always good to see other sets in the Sobell/Gec family being resurrected.

I find it fascinating to watch the evolutionary process that happens with TV chassis'.

I guess this is pretty much the same design, circuit wise as the 1000 series and uses the same valve line up? Even the PCB's look almost identical, but the physical design of the chassis has been massively simplified.

The 1000 series uses many pieces of metal, all pressed into weird shapes to form a rather random structure. It must have been expensive to produce and access for servicing, especially the line scan panel is not great.

The designers of this new range must have realised they could do it better and cheaper and have produced a much neater & tidier design. Access for servicing looks to be much better too. It must also have been much quicker and less labour intensive to assemble in the factory.

That tuner looks intriguing. Is it a combined VHF/UHF design or are there still two separate units?

Did Sobell make the wound components like the LOPT, or were they bought in from someone like Plessey? Again, nice to see that the LOPT design has been improved - it does give the impression that Sobell were trying to improve and refine their designs and were taking note of reliability feedback from the repair trade.

All the best
Nick

[Heatercathodeshort]

The tuner is a five position valve VHF unit. Some of these series used the widely used 13 channel Philips miniature tuner. Another reliable high gain unit. A separate transistor tuner is employed for UHF. Like the tuner I'm pretty sure the LOPT was manufactured by GEC/Sobell [Radio and Allied holdings] Other than the epic to clean the contacts it is an excellent tuner. It looks very 'Sobell' with not a hint of Plessey to be seen.

I mentioned that these models were manufactured at Slough but that may be wrong. It may have originated from their large factory at Hirwaun in Wales. J.