Reviving a dead Bush (TV22!)

[Ian - G4JQT]

Slightly off topic, but I read somewhere that the broadcast vision-signal black level and average brightness was better regulated in real 405-line transmissions in a way that most of our standards converters do not. Thus brightness drifts about more than it would have done on real signals and on dark scenes the black drifts to grey in simple sets like the TV22 revealing flyback lines.

It sounds plausible to me, but I know next to nothing about standards converters so it might be complete BS!

Ian

[Lloyd 1985]

Cheers for all the comments! I have rather neglected this thread for the last few days

Mark, you were lucky the lead outs didn’t come off on your TV12 tube! When I have to remove scan coils that are tight I get them as far as the base, then put my fingers round the front of the scan coils, and push on the centre of the base with my thumbs, works well, unless they are really stuck! Araldite got the highest votes over on VRAT, so I have used that on the tube base.

Andy, no need to worry about rambling, makes for an interesting read! I’ll keep that in mind about the local oscillator valve base. I also looked over that chassis! I wasn’t sure what model it was, looked like a 9” tube? I saw someone carrying it to their car when I was out in the car park, was it anyone here?

Helder, good point! I do still fancy trying it, just to see if it improves the range of available brightness/ contrast before the lines appear, most of my sets have tired tubes, and have to have it cranked up a bit, and then the lines show, particularly with the wandering brightness levels of modern content, my own fault really for using old sets to watch music videos or heavy metal concerts! Loads of flashing lights followed by dark scenes! I’ll try it on one set, then do a side by side comparison

Ian, I see you have already found the thread I saw the mods on I think you are right about earlier broadcasting standards, these days it seems anything goes! Particularly now they have HDR.

John, was it a V180C chassis? You have just reminded me I haven’t shared what happened with my own V180C! You will be pleased to know it’s in good health, working well! I had a thread on here years ago about it, back when I was just starting out in TV repairs, and I couldn’t get it going properly, mostly because of bad frame linearity. Only turned out that I’d caused it by fitting a wrong value capacitor! Something daft like I’d stuck a 0.1uf where a 0.01uf should have been… picture on it is excellent now, I had been using it most evenings back when there was stuff worth watching on tv! Maybe when I’ve finished this TV22 I’ll have to have a write up on that set. Photo of the V180C attached

Regards
Lloyd

[Lloyd 1985]

Back to the TV22

I have successfully stuck the base back on the tube, I used Araldite, the standard type. I started by putting some plain copper wire from scrap telephone wire through the pins in the base, the soldered them to the lead out wires, put some glue onto the inner edge of the base and carefully pushed it into place, making sure not to snag or bend any of the leadouts. It was left to harden overnight, held in place with tape. Once set I then checked the leads for any shorts before soldering them, then trimmed the excess off. Gave the tube a quick Megger test to make sure everything was connected up ok, it’s all good! Base nice and secure, and the scan coils fit over it too. One slight issue was noticed during testing, the CRT heater has an intermittent partial short, I only noticed because the bench power supply said over 400ma at 6.3v! I was able to clear it by gently tapping the neck with my fingers, so hopefully it won’t be a problem in the set.

The chassis is currently being pulled to bits for cleaning, the focus unit is in bits currently, and it’s cleaned up nicely, rusty fixings have been having a bath in vinegar overnight, and so far they don’t look any different… I might just give them a blast with the wire brush in the dremmel if they refuse to do anything useful! The LOPTY doesn’t look that bad, the laminations only have slight rusting, I can actually see clean metal when looking through the top of the lopt, the brackets holding it on the chassis are very rusty, so they’ll be removed for treatment. The chassis itself isn’t terrible under the dirt, it’s got the usual lumpy surface, but the white powdery corrosion cleans off ok. I did go overboard and get the brasso on it though, just to see what it’d come up like!

Regards
Lloyd

[Andy - G8MNM]

Lloyd,

Try citric acid for the rust.

You should be able to buy the crystals easily.

Just mix them up with water until dissolved and place the rusty item in the mix.

Depending on the rust it could take a couple of days for the rust to be dissolved.

Here en France I can buy the whole range of cleaning fluids - Hydrochloric/Sulphuric/Citric acid, Industrial alcohol at tye local Brico (DIY) store. They even sell them at the Supermarket.

I guess somewhere like B&Q would stock them in the UK.

Bon courage!

Andy

[Lloyd 1985]

Cheers Andy, I completely forgot to look for some at the weekend! The vinegar is doing the trick, funny thing is that the rusty parts don’t look like anything has happened, until you brush them and then the rust just falls away. I was also told that citric acid would help clean up aluminium parts that have corroded too, so I need to get some for that, I have an old Coughtrie outside light fitting that I can’t get apart because the aluminium has corroded around the glass, so I’ll have to try it on that too.

The cleanup is going well so far, the focus assembly is done, before and after pics below! I removed the lopty to keep it safe, it has the ‘T’ shaped laminations, and the only rust on them is on the ends of the ‘T’s, where it mounts to the chassis, the bit that goes up the middle of the windings only has slight surface rust, there is clean metal visible! I’m not going to try taking the laminations out at all, seems like a bad idea to disturb it if I don’t have to. I’m currently on the speaker, it was rusty, the voice coil was rubbing, the spider is detached, and something’s eaten the felt dust cover! To begin with I totally removed the cone, cleaned the voice coil with a cloth, then stuck sandpaper (p400) down the gap to loosen the rust, then used half a roll of insulation tape to get all the rust particles out of the gap. I covered the gap /pole with tape and then scrubbed the frame with coarse wire wool to shift the loose rust, then spent ages removing all the bits that had stuck to the magnetic areas! Good job I taped up the gap.. after that I cleaned the frame with IPA, and gave it a blast with grey primer followed by satin black (the only paint I had to hand…) So tonight I’ll hopefully get to put the cone back and see if it sounds any better.

Regards
Lloyd

[Helder Crespo]

This is looking great Lloyd. Thanks for posting.
I'm curious about what you will do to your LOPT. I believe a thorough drying out (at least) is important to reduce the chance of shorts.
- Helder

[Lloyd 1985]

Cheers Helder

I’m thinking of drying it by connecting it up to the bench power supply at a low current to try and warm it gently, and hopefully drive off any moisture from within, I recently tried it on a GEC lopt, but it did t work due to the windings being such a high resistance, to get any current flow that would do anything useful it needed over 100V! I gave up on that one in the end! The Bush should be doable, as others have done it successfully in the past.

Just been trying the speaker out, despite not being glued in place yet it’s sounding ok just with the headphone output of the iPad! Time to make up some shims and get the glue out.

Regards
Lloyd

[Helder Crespo]

Hi Lloyd! I imagine you will be running current through both the primary/secondary as well as through the overwind. The latter can have significant losses due to residual moisture, but the former are known to short out due to failing paper insulation: acid-damaged and moist old paper + heat + HT = bad news.
- Helder

[Lloyd 1985]

Yes, I think that’s what happened to the one in my other set, that one had a lot of rust on the laminations, so must have been quite damp at some point. I really must get round to sending it off for a rewind! I hope this one’s going to be a good one, but you never know until it fails, at least these are rewindable, unlike more modern fully potted ones.

Regards
Lloyd

[Heatercathodeshort]

The Ferguson 991T overwind has a resistance of just over 11K. The transformer was modified during production. It is wound with Eureka resistance wire to reduce capacity.
I dried out mine simply by passing through it raw mains via a variac, meter and 15W Pygmy bulb. Worked a treat. John.

[Richardgr]

Inspiring to read - you are a TV necromancer!

[Lloyd 1985]

Hi John,

That’s an interesting way of doing it! How long did you leave it? The lopty in the GEC is the least of my worries, sadly the tube is toast it had an O/C cathode, you could actually see the gap between the cathode and it’s connection, I did manage to get it to connect for a while, the picture was pretty good, but then it went again, and I ended up cracking the neck trying to get it to connect again..

Haha! TV necromancer, I like that!

Regards
Lloyd

[Lloyd 1985]

Lopty drying attempt no.1

Connected all the windings in series and set the power supply to give it 50ma, this was my power supply maxed out, it has 2 18V 5A outputs, with some buttons to keep them isolated, parallel, or series. The temperature probe is sat on top of the overwind, which seemed to be the only bit getting warm, the core was still at room temperature. I left it for a couple of hours last night and it got up to 35 degrees, didn’t fancy leaving it on overnight, so I have just fired it up again now, and will leave it on for the day.

Regards
Lloyd

[Helder Crespo]

Originally Posted by Lloyd 1985

Lopty drying attempt no.1

Connected all the windings in series and set the power supply to give it 50ma, this was my power supply maxed out, it has 2 18V 5A outputs, with some buttons to keep them isolated, parallel, or series. The temperature probe is sat on top of the overwind, which seemed to be the only bit getting warm, the core was still at room temperature. I left it for a couple of hours last night and it got up to 35 degrees, didn’t fancy leaving it on overnight, so I have just fired it up again now, and will leave it on for the day.

Regards
Lloyd

Hi Lloyd,
I'm really curious to see how your dried-out LOPT will behave, in particular how the EHT will change with increasing brightness / beam current.
- Helder

[Heatercathodeshort]

I applied the AC via the variac for around two days. Result is excellent. J.

[Helder Crespo]

Originally Posted by Heatercathodeshort

I applied the AC via the variac for around two days. Result is excellent. J.

Did you seal it after drying? Perhaps a thin coat of anticorona varnish?
- Helder

[Heatercathodeshort]

No, I left it as it is. Once you seal it nothing can be done other than rewind it. These transformers never looked pretty but work ok if left alone. J.

[Helder Crespo]

Originally Posted by Heatercathodeshort

No, I left it as it is. Once you seal it nothing can be done other than rewind it. These transformers never looked pretty but work ok if left alone. J.

Ok, thanks. But how to you prevent moisture from infiltrating the windings again? I imagine you have to keep the set dry and perhaps also use it regularly? Thanks.
- Helder

[Lloyd 1985]

That’s what worries me about soaking them in modern varnish, if moisture does find its way in again, it’ll be much harder to drive it out. I fired up my first TV22 yesterday for the first time this year, it came up fine, and stayed good for the half hour I left it! That one has never had any lopty drying done, or indeed anything at all done to the transformer! The tube is nice and bright in that set, it’s an MW22-18 straight gun, and it has an ion burn the size of a tennis ball! Not too noticeable when watching anything though.

I got another power supply involved in the lopt drying session yesterday, got the current up to 65mA, I also moved the thermometer probe closer to the core, as it was warmer there, got it up to 61 degrees and left it on all day whilst I did some gardening. You could see the pitch had gone from dull grey/ black to a more shiny black, and it had become slightly soft too.

I’m on holiday at good old Anderby creek now until next Friday, so nothing will be done on the set until then. I was tempted to bring it with me just in case I get bored, or it rains!!

Regards
Lloyd

[Heatercathodeshort]

These receivers were probably used daily from around 1950 to maybe 1960. The much more usable TUG24/TV24 tended to carry on a bit especially with the much older generation.
This daily switch on dried any moisture preventing LOPT breakdown.
They were then placed in damp sheds and lofts for 60 years resulting in the pitch, being hydroscopic became contaminated with damp.
Once dried out and used occasionally in a centrally heated home there should not be a problem with recontamination. There is no golden rule or cure. Do whatever you feel happy with. The main cause of breakdown today is a shorted primary to secondary winding, not the overwind. These transformers were very reliable in their day. The TV22 was well on it's way out when I entered the trade but I did service quite a number of TV/TUG24s and never encountered a duff Lopt. John.