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B&W TV GEC BT-2147, let the fun begin!

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Lloyd
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@slidertogrid, those tag strips were a great idea, there are some in the GEC, but they are buried under the components! The ‘snip and tack another in’ method of replacing components for a quick test doesn’t really work with this set, as you end up with legs touching others. The cabinet is really flimsy too, since the chassis is only bolted to the bottom of the cabinet, there is nothing between the bottom and top to brace it, where the TV22 has the chassis bolted half way up the cabinet, also with some strengthening, they just feel more solidly constructed. The one thing I do like about the GEC is that you don’t have to faff about trying to undo hidden screws to get the knobs off! In fact, the knobs stay on when removing the chassis from the cabinet.

It’s interesting that the sale of the set pre dates their online history! So the previous owner may have had the set hanging around for more than 20 years, and did nothing with it! Well, apart from discover the tube was naff… 

 
Posted : 30/06/2024 10:26 am
slidertogrid reacted
slidertogrid
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@cathovisor  🤣 I laughed out loud when I read that! I have a 145 which I bought working from another collector so I haven't had to do any work on it so far...!

I have a RAP which has flashing and burning on/under the wavechange switch, that too looks like a thing of nightmares... It's been hidden in the spare room for a long long time... 

 
Posted : 30/06/2024 1:00 pm
Cathovisor
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@slidertogrid I should also add that I have a particular disdain for the person at Ultra who thought a good place to put the AVC decoupler on the little T401 table set was buried between the wavechange switch front plate and the chassis, against the top edge of the chassis 🤨 I'm very fond of T401s (they work really well for a short superhet) but I wince every time I come to restore one.

 
Posted : 30/06/2024 6:54 pm
slidertogrid reacted
Lloyd
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Well, someone else has been at this set before me, not only did they disconnect the CRT heater, they also disconnected the video lead that goes from the RF chassis to the main deck, and reconnected it to entirely the wrong place… 

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it’s the orange wire in the above photo, which was also too short making it very difficult to attach it to the RF chassis. I replaced it with the white wire in the photo below, connected to the correct place this time!

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And as if by magic, we now have some picture information on screen!

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the line speed is way off, and it just generally looks crap, but it’s a start! Oh, the frame output transformer primary went pop again, and no amount of zapping would revive it, so I’ve bunged in a mains transformer from a portable radio… it measured near enough, so I thought I’d try it! It sort of works! I think it’s upside down though. The phantom twiddler has been at the RF deck too.. but I have managed to get sound and vision on channel 1.

 
Posted : 01/07/2024 7:28 pm
slidertogrid
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Nice to see it is going in the right direction! I hate it when I find something has been had a go at and then abandoned! I have a couple of frame transformers removed from scrap chassis so if your mains transformer doesn't do the trick once you have the output stage working let me know and I will have a look to see if I have anything suitable.

Rich

 
Posted : 01/07/2024 8:26 pm
Lloyd reacted
Lloyd
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Cheers Rich, We'll see how it goes!

Now I was ready to give up on this set, as I wasn't getting anywhere with it earlier in the week, the line speed was way off, so was the frame speed, and I was unable to rectify the twiddling of the RF deck, and in the end I lost the small amount of picture I had!

So I have had some time away from it, and come back with a much needed fresh enthusiasm. First job was to get the line and frame speed within spec, now I'd already replaced most of the capacitors by this point, and had run out of options on that front! So onto the resistors, first one I looked at was R45 (on Trader sheet 976/T8), it's in series with the slider of the line hold control, and should be 130k, mine read 166k, I didn't think it'd be that simple, but it was! that got line lock as soon as the set was switched on, so onto the frame speed, R67 is in series with the frame hold control, should be 470k, but came in at 678k! new one in, and now the hold control sits about 1/4 away from the bottom end. Whist I was at it, I managed to tune the RF deck to somewhere close enough to get sound and vision, and it needs the sensitivity turned down otherwise the picture washes out.

So here it is so far!

IMG 1591

just need to have a poke at the frame stage to see if I can correct the linearity. The picture is very dim, and I need to play with the focus, but it's getting there!

 

 
Posted : 06/07/2024 7:31 pm
LSmith, crustytv, Jayceebee and 1 people reacted
Lloyd
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Some more progress, found the source of the terrible frame linearity! It’s my bodged in frame transformer, I managed to get the original one working long enough to get a decent linear picture.

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it doesn’t look too bad once the tube has warmed up enough!

This is the offending frame transformer, can’t remember the exact resistance of each winding without the circuit in front of me, I’ll put the values in later.

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I think the lopty may have a bit of trapped moisture in it, as the focus drifts off after 20 minutes or so, and the picture gets dimmer, I haven’t checked the EHT level yet, but I think I’ll have a go at warming it up to drive it out, see if that improves it. As of now though, I have removed the CRT so I can flip the chassis to get to the components underneath easier, as it all needs a little tidy up!

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Posted : 13/07/2024 9:05 am
freya, LSmith and Nuvistor reacted
irob2345
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Trapped moisture in wax-paper-cotton LOPTs is getting very common, with the fading-away over 5 or 10 minutes symptoms. I've restored several to health this way:

  • Using a slow electric cooker (not gas!) on "Hi" OUTDOORS, boil the transformer(s) slowly in turps (aka mineral turpentine, paint thinners) until the bubbles and foaming stops, indicating all the water has been vaporised and driven out. This process also dissolves the wax, which is hygroscopic so you want it gone. You will be surprised by the foaming at the ends of paxolin tag panels, paxolin contains water too! This can take a few hours.
  • Take the transformer(s) out and place gently on a cooling rack.
  • Put plastic sleeving over the solder tags to make the later tasks easier.
  • Soak the transformer in oil-based clear polyester lacquer (we have "Estapol" here). DO NOT use the clean-up-in-water variety, check the label.
  • Take it out and leave it for a day or so to set properly. If you need to fix or replace the anti-corona donut, use hot-melt glue and a hot air gun.
  • Repeat the soak, dry, set cycle two more times.

This results in a very robust repair that should last 100 years!

Oh, when doing the turps boil, keep a suitable fire extinguisher handy in case of accidents. Turps is flammable.

 
Posted : 13/07/2024 10:34 am
Lloyd reacted
Lloyd
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I’d love to be able to do that! Actually, I think there was an old slow cooker lying unwanted at my Nan’s house, unless one of my other relatives has snaffled it! For now, passing current through it to get it warm for a while will have to suffice, but I do remember the last GEC of this type that I tried it on needed quite a high voltage to get any current to warm it up.

 
Posted : 13/07/2024 3:31 pm
freya reacted
Cathovisor
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You could try and get an old Baby Belling, Lloyd - it's what I use for getting condenser blocks apart.

 
Posted : 14/07/2024 1:59 pm
Lloyd reacted
slidertogrid
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Posted by: @lloyd

 I do remember the last GEC of this type that I tried it on needed quite a high voltage to get any current to warm it up.

I have had success with the pitch overwinds that Bush Murphy were so keen on, using this method. I found 30V would get the overwind hot. On a couple there was brown froth appearing around the hole where the core goes through so I guess it is the cloth bound inner part that was the problem.  I left it running for three days and then tried them, the last three I did have been OK. I admit I do feel that I was lucky. I don't expect it to work every time.   With these transformers I dry them out before trying them first now. 

Rich.

 

 
Posted : 14/07/2024 7:19 pm
freya reacted
Lloyd
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This set is the gift that keeps on giving! And trouble is what it’s giving… I thought it was going rather well, I’ve pretty much finished changing caps, just a couple of dodgy tacked in replacements awaiting their eviction. The Lopty has had some heat treatment by shoving 30V through it (this lopty is different to the one in the other GEC!),

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which sort of worked, it still goes out of focus after half an hour or so, but blasting cool air at it with a fan keeps it happy for longer. Since it was all going so well I thought I’d stick it back in its cabinet!

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That’s still with the CRT heater running from the bench power supply, it gives a pretty good bright picture when you accidentally crank up the current to nearly 500mA! Oops… it’s still alive though! It didn’t pop!

…But something else has!!! Don’t know what yet, but I fired the set up the other day, and watched a bit of YouTube whilst I waited for it to warm up. Half an hour went by and I suddenly remembered I’d switched it on earlier! But nothing was happening.. it was totally dead! The only thing glowing was the CRT heater, which was still being fed from the bench PSU, nothing else happening within the set, not even any heat from the dropper! The set is getting power, the fuses are still intact, so I guess it’s either a valve gone O/C, or the dropper has popped (I hope not!).

Gotta love these old telly’s!

 
Posted : 20/08/2024 6:01 pm
Lloyd
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Found it!

The remaining functioning pole of the mains switch went O/C! I say remaining functioning pole because the other pole had been bypassed already, not by me! So because I’m lazy and couldn’t be bothered to pull it out of the cabinet again, I decided to try and make it work again, so set about it. I connected up the meter on continuity, and on switching it on there was nothing, but as you turned the switch back to off there was a quick beep from the meter. So if you turned it on, then turned it back to just before it clicked to off and let go, it would then stay on! This also worked on the other failed switch pole, so I thought maybe it just wants cleaning, but how to get any cleaner inside it? I tried by one of the solder tags, blasting some servisol at it in the hope it would get inside, it didn’t, so I went for the seam between the switch and the pot and blasted it in there. Some must have got in as the switch is now working again!

Now to find a suitable way of powering the tube heater, preferably without blowing it open…

 
Posted : 23/08/2024 8:56 am
slidertogrid
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@lloyd Dried up grease in the switch at a guess, preventing the contacts from fully closing, it will probably be OK for another 60-70 years now!  What voltage are you running the heaters on?  I may have a suitable heater boost transformer.

Otherwise if the CRT is last in the chain or can be made so there was always the old dodge of putting a high value and fairly high wattage resistor from the mains to the 'hot' side of the heater. I think in the case of a 6.3V heater it was about 1K but if your heater is lower voltage you may need to at least double that. I have seen a RS 'polo' section used, fixed to the chassis for heatsinking back in the bad old days of keeping 'em going on a shoestring. Some careful experimentation of the value may be needed as you say you don't want to burn it out...

 
Posted : 23/08/2024 9:48 am
Cathovisor
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Posted by: @lloyd
I tried by one of the solder tags, blasting some servisol at it in the hope it would get inside, it didn’t, so I went for the seam between the switch and the pot and blasted it in there.

I've drilled a 1/16" hole in a switch before now to do that. I do wonder how that WD-40 manufactured switch cleaner would fare in this application.

 
Posted : 23/08/2024 1:01 pm
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