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Old 26th Jan 2020, 7:25 pm   #1
Syrinx1
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Default Grade 1 Class H winding wire

Hi,

What are members opinions on using Grade 1 winding wire for mains and audio output transformers in valved equipment? I would assume it would be ok providing sufficient interlayer insulation is used, but might be wrong?

Any thoughts / opinions on this?

Jonathan.
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Old 26th Jan 2020, 9:35 pm   #2
kalee20
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Default Re: Grade 1 Class H winding wire

Class H is OK, pretty commonplace these days (180°C continuous rating).

Grade 1, on the other hand... I'd rather use Grade 2. Thicker enamel. Down side is you may need to drop a wire size, so resistance will increase slightly. But unless the design is at the limit, I'd rather the extra reliability.

And, interlayer insulation might be unnecessary then, so you won't need to drop the wire size after all! Most modern mains transformers have no interlayer insulation. As long as the winding is wound progressively, and you haven't got big gaps so the last turn can slip down and touch the first turn, you'll be OK.
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Old 29th Jan 2020, 11:03 am   #3
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Default Re: Grade 1 Class H winding wire

Would vacuum pressure impregnation mitigate some if the risk from using grade 1 wire?
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Old 29th Jan 2020, 11:48 am   #4
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Default Re: Grade 1 Class H winding wire

Not really. There is already turn-to-turn contact of the varnish coating on the wire, forming the easiest path to break down. Impreg varnish merely surrounds these areas. It will help prevent fretting under vibration, but the bottom line still remains as two layers of the wire's own coating, and the probability of flaws in it. Turns have to touch a lot, or there would be nothing supporting them before impregnation.

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Old 29th Jan 2020, 3:14 pm   #5
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Default Re: Grade 1 Class H winding wire

Thanks David / Kalee20.

I suppose reducing the voltage difference between layers and adjacent turns would help if I can accommodate this in the transformer design, but then I'm really starting to complicate the design and will end up loosing significant window space.

Maybe I'm best off ordering some grade 2 wire and weighing the grade 1 stuff I have in at the scrap merchants!
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Old 29th Jan 2020, 4:23 pm   #6
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Default Re: Grade 1 Class H winding wire

You would be better, yes. How much better, is debateable.

I work in the hi-rel industry so reach for the better wire as standard practice. But Grade 1 is used a lot 'out there.' It can give a slightly lower winding resistance. And the world hasn't ended in a cataclysm of transformer fires, as yet.

Bearing in mind that you are (I presume?) an occasional winder, without polished-smooth wire guides, the Grade 2 will be more forgiving of the occasional scrape in winding.

For the cost of a few quid, I'd do it.
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Old 30th Jan 2020, 9:36 am   #7
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Default Re: Grade 1 Class H winding wire

Ok thanks.

Will be busy over the next few weeks, but when I make a start on winding, I'll post details of progress. It would be really informative if people could critique as I go.
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Old 30th Jan 2020, 2:47 pm   #8
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Default Re: Grade 1 Class H winding wire

Use the grade 1 wire for prototyping and trial runs.
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Old 30th Jan 2020, 8:29 pm   #9
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Default Re: Grade 1 Class H winding wire

Good idea! Thanks.
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Old 1st Feb 2020, 1:20 pm   #10
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Default Re: Grade 1 Class H winding wire

For my first (Experimental) transformer for fixed bias, push pull pair of EL91 in push pull for a guitar amp, I was thinking of trying the following:

EI76 51mm stack,

380 x bifila 0.1mm wire in 2 layers,
17 x 0.71mm wire in 1 layer 2ohm secondary,
760 x bifila 0.1mm wire in 4 layers,
7,10 and 14 x 0.6mm wire in 1 layer for 4,8 and 16 ohm,
380 x bifila 0.1mm wire in 2 layers.

0.2mm insulation between layers except between primary and secondary which would have 0.5mm insulation.

Does this seem reasonable or sm I way off the mark?
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Old 1st Feb 2020, 4:14 pm   #11
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Default Re: Grade 1 Class H winding wire

If bifila means bifilar and one wire is connected to one anode and the other to the other anode, then there will be twice the HT between the wires so will need very good wire insulation. The voltage will not be higher between layers so interlayer insulation will not help but may enable a neater job to be done.
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Old 1st Feb 2020, 7:27 pm   #12
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Default Re: Grade 1 Class H winding wire

Yes sorry, predictive text on my phone, I mean winding in parallel.
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Old 1st Feb 2020, 8:59 pm   #13
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Default Re: Grade 1 Class H winding wire

Bifilar winding the two primary sections in a P-P transformer will give the best possible coupling. But I've only ever done it with low-voltage transistor amplifier. I just wouldn't trust the insulation on a valve jobbie.

You might get away with it for DL92's, operating at 90V HT. But that's as high as I'd want to go.

Bear in mind that at max signal, there will be (instantaneously) nearly the full HT voltage between the strands, right along the whole length of the wire pair. Just like Trevor said. It's asking a lot. Plus, you'd probably like to think that if anything silly happened, like the speaker got disconnected, that the transformer might survive without an internal breakdown.
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Old 1st Feb 2020, 10:08 pm   #14
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Default Re: Grade 1 Class H winding wire

Sorry, I think Bifilar was a poor choice of word.


What I intended to do was to wind 2 strands of narrower guage wire of which I have copious amounts in place ok a single larger wire to give equivalent total current rating of a single large wire.
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Old 1st Feb 2020, 10:35 pm   #15
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Default Re: Grade 1 Class H winding wire

Hi Yes, where 2 wires are used in parallel there will be a minimal voltage between adjacent turns so Gr1 should be no problem.
Depending on diameter it will affect the packing factor, but it is a common production technique where only one type/size of wire is being used the transformer and it is being made in large volumes

Ed
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Old 2nd Feb 2020, 1:04 am   #16
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Default Re: Grade 1 Class H winding wire

Thanks Ed.

The core I'm using is quite large when considering a pair of EL91's only put out about 5 watts, but the large core gives me more window space. The valves are high impedance - aprox
20 k anode to anode, so I'm hoping the larger core will help with low frequency response and require a lower number of turns.

Though considering my earlier confusion over the meaning of bifilar these assumptions might be wrong?
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Old 2nd Feb 2020, 8:00 am   #17
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Default Re: Grade 1 Class H winding wire

Hi again, by using a larger core than strictly necessary you can reduce the flux density in the core to say 0.6 Tesla or less as well as reducing the LF rolloff point to say 20Hz.
Transformer design is an iterative process and there are many tradeoffs.

Ed
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Old 2nd Feb 2020, 6:03 pm   #18
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Default Re: Grade 1 Class H winding wire

'Bifilar' simply means two-wires, ('fils') in French for instance. So you're not wrong, it just wasn't clear how you were going to connect the two strands.

But it is clear now, and the good news is that it won't be a problem!
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Old 2nd Feb 2020, 6:44 pm   #19
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Default Re: Grade 1 Class H winding wire

That's great, though embarrassingly I was getting confused. It will now just be a single wire of the 0.1mm guage for the primary. I think this has sufficient current rating?, the bifilar idea was when I was initially thinking of using .063mm wire. Using 0.1mm also reduces the number of layers needed in the central half primary section to 3 layers rather than 4.
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Old 2nd Feb 2020, 8:34 pm   #20
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Default Re: Grade 1 Class H winding wire

Hmm... Going below 0.1mm starts to add to handling challenges. Even soldering the stuff, you have to be quick else you find you've completely dissolved away your stripped end!

So yes, single 0.1mm rather than bifilar 0.063mm!
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