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Old 2nd Mar 2021, 7:09 pm   #221
Travellingwave
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Default Re: My first telly TV22

Are these likely to be any good?

https://www.cricklewoodelectronics.c...itors-1KV.html
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Old 2nd Mar 2021, 8:30 pm   #222
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Default Re: My first telly TV22

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Ceramics are less stable with temperature and normally not a good choice for tuned circuits. Cricklewood doesn't stock silver mica. Farnell has a large selection of dipped silver mica caps, including many from Cornell-Dubilier's CD series. I got mine from justradios in Canada. Shipping time to the UK is (was...) typically 1 week. There are some on eBay for exorbitant prices (£8 per piece) from companies who basically order them from Farnell and them post them to you.
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Old 2nd Mar 2021, 10:13 pm   #223
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After a few hours in vinegar to remove the worst of the rust , a quick blast in the AGA to dry out, followed by a light rubbing with bees wax since this is what seems to have been done in the origional construction, then into a vice to squeeze it all together and back into the AGA to hopefully stick the whole lot together. All reversible if necessary
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Old 3rd Mar 2021, 9:29 am   #224
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Default Re: My first telly TV22

Core ready for rewinding
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Old 7th Mar 2021, 8:34 pm   #225
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Default Re: My first telly TV22

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Core ready for rewinding
In case you're rewinding it yourself, I remember reading somewhere on the forum that the secondary is wound approx. one inch away from the edge of the primary, which is important to get the right coupling / interwinding capacity & inductance. I imagine this is common to all TV22 lopt models. You probably noticed and recorded this during your unwinding, but in any case I thought I should mention it.
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Old 7th Mar 2021, 9:38 pm   #226
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Hi Helder
I have made a start on rewinding. From my unwinding I noted that the first layer of the secondary (which is the first layer to be wound) is started about halfway along the core and wound towards the bottom on the Core. This forms the first 60 turns of the secondary. There are then a couple more full layers of about 155 turns per layer to forms the rest of the secondary ( working from memory now so dont quote me)

Primary is a couple of full layers of 155 turns , followed by I think 8 layers with a final 1/2 layer.

So not sure if the start and end half layer is what you are referring too?

I started with 0.2 mm wire but after the first 60 turns found the resistance was coming out higher than what I had measured on the origional , so I swapped to 0.25 which is coming out closer. Not sure how important resistance is at the end of the day.

The main challenge I have found with the rewind in getting each subsequent layer to start and end in the right place so the windings don’t fall over the edge of the layer below.

I have been putting a layer of magneto tape between each layer , so should be electrically sound but time will tell if it will end up too fat to fit into the overwind. Still have the final 1000 turns of the primary to go.
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Old 7th Mar 2021, 9:58 pm   #227
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I started the first layer of the primary and the end of it fell off the end of the secondary winding below, I don’t think I got a good start to this first primary layer. So I’m going to start the primary again but this time I will pot the ends of the secondary winding in wax to give a solid base to start winding the primary on.

As you can probably tell I am very much making this up as I go
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Old 7th Mar 2021, 10:14 pm   #228
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Default Re: My first telly TV22

This was the start of the first layer
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Old 7th Mar 2021, 10:19 pm   #229
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Default Re: My first telly TV22

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I started the first layer of the primary and the end of it fell off the end of the secondary winding below, I don’t think I got a good start to this first primary layer. So I’m going to start the primary again but this time I will pot the ends of the secondary winding in wax to give a solid base to start winding the primary on.

As you can probably tell I am very much making this up as I go
I think you're doing an amazing job. I think it's important that you recheck the wire gauge, as any % change with respect to the original with translate into the same change in the final diameter and the whole thing may not fit in the end.
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Old 7th Mar 2021, 10:50 pm   #230
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Default Re: My first telly TV22

Thanks Helder

Yes I will see how I go with 0.25 - if it ends up to big I will have to redo it with 0.2mm wire - I'm kind of treating it as a dry run and if I end up with something that fits that is a bonus.

How important is winding resistance likely to be

Below is link to video on Youtube

https://youtu.be/WiO8y6BmAno
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Old 8th Mar 2021, 2:47 pm   #231
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Default Re: My first telly TV22

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Thanks Helder

Yes I will see how I go with 0.25 - if it ends up to big I will have to redo it with 0.2mm wire - I'm kind of treating it as a dry run and if I end up with something that fits that is a bonus.

How important is winding resistance likely to be

Below is link to video on Youtube

https://youtu.be/WiO8y6BmAno
I would say that the resistance is important, e.g., it can affect the resonance conditions of the secondary (with its capacitance and inductance + resistance) + 470pF tuning cap. But other members with more knowledge and experience on lopts should be of greater help here.
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Old 8th Mar 2021, 3:04 pm   #232
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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?
The overwind is a work of art, at least by my standards. It's wave wound (this can be appreciated in a stripped and varnished lopt) to keep its self-capacitance as low as possible, otherwise you could need a negative capacity in place of the +470pF tuning cap (think of a sheet of kryptonite coated with a film of unobtanium, or perhaps this: https://phys.org/news/2019-04-newly-...capacitor.html). I have no experience on this type of winding whatsoever but I've read that it requires special wire with high-friction ("sticky") insulation rather than enamel, as well as the right gauge, which is hard to find nowadays. Litz wire, according to this: https://en.wikipedia.org/wiki/Basket_winding
If your overwind is in good shape, like they usually are, the varnish coating should be all it takes to keep it working well for many more years.
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Old 8th Mar 2021, 7:51 pm   #233
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Default Re: My first telly TV22

Yes having had a go at the fairly basic main winding I would not fancy trying the overwind
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Old 8th Mar 2021, 7:57 pm   #234
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As I mentioned the ends of the winding we’re getting a bit tapered where the overhanging inter layer tape was getting squashed together - this was making it increasingly difficult to keep the ends of the winding from falling off. So to give a nice flat surface for the final 1040 turns I wrapped some paper round the winding and poured some molten beeswax into the gap formed by the paper. This has some a pretty good job of building the ends back to a level surface.

Not sure if the is the correct method or a bodge
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Old 8th Mar 2021, 8:02 pm   #235
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Recon my winding is already getting a bit fat at 20mm diameter. ID of overwind tube is 26mm so that only leaves 6mm/2 = 3 mm for the final layers. In theory it’s possible but need to keep things tight.
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Old 8th Mar 2021, 9:11 pm   #236
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Default Re: My first telly TV22

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Recon my winding is already getting a bit fat at 20mm diameter. ID of overwind tube is 26mm so that only leaves 6mm/2 = 3 mm for the final layers. In theory it’s possible but need to keep things tight.
Looking forward for the final result and test. One thing I'm curious about is how well the rewound lopt will behave in terms of EHT regulation, namely if there's any image size dependence on brightness (assuming the contrast setting is not excessive). Hopefully not, but it can definitely happen even when everything else (resistance, capacitance, inductance) measures as expected, the EY51 is in good shape and the value of the tuning cap is optimised, as well as the other adjustments in the line output stage.
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Old 8th Mar 2021, 9:15 pm   #237
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Default Re: My first telly TV22

Hi TW, you could go down to 0.22mm wire as resistance is not so important as correct positioning of the windings relative to each other (self capacitance of windings).
I normally use type 56 polyester tape for the insulation, which from memory is about 2 thou thick.
If you have problems when you have it rewound then it is possible to vary the 470pF silver mica cap a bit to repeak the tuning

Ed
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Old 9th Mar 2021, 11:30 am   #238
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Default Re: My first telly TV22

Thanks Ed

I had a late one last night and got it all back together - it just fitted into the overwind tube - but a snug fit. So I think 0.22mm would be the right size.

The other thing I would do different next time would be to take more care with where the tails exit the core relative to the terminals that they have to connect too - and also to get some sleeving onto the tails as I go along.

Lets see if it works!!
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Old 9th Mar 2021, 12:25 pm   #239
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Default Re: My first telly TV22

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Originally Posted by Ed_Dinning View Post
Hi TW, you could go down to 0.22mm wire as resistance is not so important as correct positioning of the windings relative to each other (self capacitance of windings).
I normally use type 56 polyester tape for the insulation, which from memory is about 2 thou thick.
If you have problems when you have it rewound then it is possible to vary the 470pF silver mica cap a bit to repeak the tuning

Ed
Hi Ed. I believe the adjustment of the silver mica cap is not really a repeak, but finding the right setpoint somewhere around the peak. The reason I'm saying this is because on the TV24 this cap has 300pF, with everything else the same as the TV22. The lower value results in slightly higher EHT (approx. 500V more, I think), as required by the larger tube on the TV24. In my set I had to add 200pF to the 470pF in order to get the right width and EHT from my rewound lopt. I still have losses in the primary circuit when I turn up the brightness - the temperature of the EY51 filament clearly drops as the brightness is increased - but I haven't been able to find out what is causing the fault. The metrosil is fine as well as all the caps. The PL38 and PZ30 are NOS but the behaviour is the same as with the original valves. Do you have any ideas?
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Old 9th Mar 2021, 8:45 pm   #240
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Default Re: My first telly TV22

Hi Helder, yes it is simply a matter of "tune for maximum smoke", I'm not aware of any measurements that can be taken to determine the correct point

Ed
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