Re: My first telly TV22
 

Hi
This is impressive! Looking forward to your video and results.
Helder

Re: My first telly TV22
 

Your use of an Arduino for the wire feed guide could mean it also has the potential to work as a wave winder as well.

I was wondering about that - in principle I see no reason why not - its just an electronic cam function - in my day job I do a lot with multi axis servo systems and robots and this is a standard function - should be possible to implement with steppers - probably using Gcode would be the easiest way.

I read somewhere that the wire is impossible to get hold of if you were to try to rewind the overwind for example - but what is special about it?

Re: My first telly TV22
 

So I cobbled together my coil unwinding machine and dissected the LOPT windings.

I am in the process of uploading a video to youtube and will share it once that is done.

As far as I could tell there may have been two places where the primary and secondary were connected - one at the end of the last layer of the primary , the paper seems very crumbly at the ends of the winding, but also there was another fault somewhere in the middle of the last layer.

Overall a straightforward operation - lets see how putting it all back on again works out!!.

Re: My first telly TV22
 

Here is link to video. Will try to get rewind done some time next week work permitting.

https://www.youtube.com/watch?v=SKLh...ature=youtu.be

Re: My first telly TV22
 

Thanks for the video!
What was your turn count in the end?
Helder

Re: My first telly TV22
 

Pretty much as posted by Andy(Beery) give or take a turn.

Re: My first telly TV22
 

Here is the final score

The paper used between layers measured at 0.11mm thick , so the magneto tape I have is thinner than this

Re: My first telly TV22
 

Thanks. Your turn count is really spot on. As for the paper thickness, I think your measurement is a bit off. A standard A4 sheet is 0.1 mm thick (hence 500 sheets make up a 5 cm tall pack). The paper in the lopt is surely thinner than an A4 sheet.
Helder

Re: My first telly TV22
 

I agree,
it must be thinner than that.
When measuring such small things as paper insulation or even wire diameter, I always use a micrometer, which is much more accurate than a caliper.

Good to know my turns count wasn't far off.

Cheers
Andy

Re: My first telly TV22
 

Based on the post-mortem, where do you reckon the short took place? From your video it seems to have been roughly in the middle of the central portion of the coils. Quick question: I known it can be very hard to determine, but were you able to check if the paper was / had been impregnated with white spirit in that area? As for the rusty ends of the laminations, my varnished lopt was in a very similar condition to yours. I think that if the problem is only at the top/bottom, this should not make a huge difference in performance (the magnetic circuit is open/lossy anyway), apart from potential vibrations that can be minimised by tightening and restraining the ends. The rust layer is actually an insulator, provided it is dry (or immersed in white spirit) and then varnished.
I never fully disassembled my lopt. Prior to varnishing, I simply squeezed the laminations together and machined a small restraining piece to keep them together (see photo below).
Helder

Re: My first telly TV22
 

Hi Helder
I think there may have been two faults , one at the end of the final layer and one in the center of the final layer.

My impression is that the white spirit hadn’t reached into the center of the windings. The winding when originally done seems to have had molten wax brushed on ( I’m guessing) so my impression is of an homogenous mixture of wire/paper/wax and no smell of white spirit.

I’m pretty sure that white spirit/varnish would help with reinforcing the insulation at the ends of the windings which is probably where most faults would occur.

As for the thickness , I am probably measuring wax and paper , the paper/wax has the impression of the wire embossed into it , so the actual paper may well be thinner

Re: My first telly TV22
 

Hi Folks, a piece of heavy duty heatshrink tube works wonders in keeping the lams together

Ed

Re: My first telly TV22
 

Hi
Thanks. Wax & paper are definitely not a good combination (think capacitors). Based on your results, I think it is unlikely that any varnish has made it to the central portion of the windings in my lopt, so I agree with you that the protection is mostly at the ends. On the other hand, the white spirit and varnish (given enough immersion time) should be able to infiltrate into the very same areas where humidity (and air) tend to go to, and hence where reinforcement is more important and necessary. I don't know how long my varnished lopt will last, but Argus25's TV22 lopt was "turped & varnished" many years ago (10+?) and is still going strong, whereas my first lopt (left original and untreated) lasted for a few hours prior to developing the dreaded short.
Helder

Re: My first telly TV22
 

Thanks Ed. I did consider that option, but given that I didn't disassemble my lopt, the accessible area was rather small, hence the machined retaining ring.
Helder

Re: My first telly TV22
 

I guess in due course I will discover if dismantling this thing was a good idea or not. But it’s an interesting learning curve and if I get stuck hopefully I can send it to Ed to be properly done!

Re: My first telly TV22
 

I suppose a halfway house would be to remove the inner windings and immerse those in a very much thinned down varnish , even better under vacuum. That way you would not make it very difficult to remove again later if a fault did occur.

The transformer varnish I used ( from RS components) seems to dry to an almost caramel consistency to is quite easy to crumble off if needed. Not sure standard varnish would be as easy to remove for reworking if needed.

Re: My first telly TV22
 

Ok. Please remember that you'll probably have to adjust the 470pF tuning cap (increase or decrease the capacity) in order to get the lopt resonating near its maximum efficiency. Once you install it, the mismatch will be noticeable in the raster width. Too narrow, you need to increase the capacity; too wide, decrease it. With the rewound lopt in my first TV22 I had to add 200pF. I used a 1000V-rated dipped silver mica. Just don't use standard 630V poly caps; a 1000V one will probably survive, but will introduce more losses than the silver mica cap.
Helder

Re: My first telly TV22
 

Peak voltage across the capacitor is 830 volts

Re: My first telly TV22
 

Ok thanks for the info

Lams are in vinegar deejaying

SHMBO not impressed at consumption of good wine vinegar

Re: My first telly TV22
 

Derusting i mean