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Old 13th April 2004, 07:21 PM   #51
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Indeed an air-cored transformer has simply too much leakage inductance to be useful. It can work however at HF with tuned circuits but not for audio IMHO.

Thoriated,

You are right about neat winding a choke. It maximises fill factor, that is, the most copper in the least space. For that purpose there is also wire with a square or rectangular cross sectional area. But your idea with epoxy doesn’t work that way. When you heat epoxy to get it more flowing, it hardens in a few minutes and does not get much chance to creep capillary into the windings. There are special potting epoxies and polyurethanes for this purpose that harden more slowly at high temperature but they need vacuum impregnation anyway for good results.

There is also special wire called “Backlackdraht” or “Thermo setting magnet wire” for this purpose. It contains an extra layer of polymer that melts at 140 - 150 deg C. If you heat the final coil in an oven at 150 deg C the windings bake firmly together. Also you can bake each laid winding separately with a hot air gun, but that takes some practice.

Cheers
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Old 13th April 2004, 07:34 PM   #52
Fuling is offline Fuling  Sweden
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Last time I made a pair of output transformers I did like this:

After winding a layer I "painted" it with a generous coat of shellack. Quickly after that I covered the layer with a strip of kraftpaper which also was soaked in shellack.
After that I dried everything with a hairdryer before I continued with the next winding layer.

I used two different paper qualitys, one thin (McDonalds bags )
between the layers and grocery bags (much thicker) between primary and secondary sections.

I guess a similar technique could be used for making air core inductors, a roll of hard paper could serve as a bobbin.
Those big aircore chokes I found in the junk pile at my brothers work seems to be made more or less like this.
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Old 14th April 2004, 03:05 PM   #53
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Default air core???

hmmm... so I should look for an air core inductor?

Or just a spool of 12ga copper wire with a DCR of 1 ohm?

Isn't its capacitance going to incease with a air core inductor vs an iron core one?

what about cost factor?? and size?

Thanks!!!

p.s. where can I search for these things?
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Old 14th April 2004, 03:58 PM   #54
Magura is offline Magura  Denmark
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According to Nelson Pass an aircore should work fine for ZV7

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Old 14th April 2004, 04:24 PM   #55
Fuling is offline Fuling  Sweden
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Magura:

Whatever Nelson says
Thinking of it, why would the inductors have to be coupled?
The resistors in the original circuit are not coupled...

I have this idea that by using coupled inductors we approach PP operation (just look at any regular PP tube amp), but when the inductors are separated from each other it turns into balanced SE operation instead (imagine two bridged SE tube amps).

If there is any truth in my theory there should be a big difference in efficiency, since the version with coupled inductors would make it with half the bias current.
I think there is an article somewhere at Tube Cad Journal that supports this theory, at least parts of it.

Audiogeek:

No idea what you should look for, actually!
If you find suitable rolls of wire with both ends free you´ll probably have to soak them in epoxy or something (a science by it´s own it seems) since they´re not very tightly wound.
Use them as they are and they will probably make more noise than the loudspeakers

I don´t think winding capacitances is much of an issue here.
At least it is not when using iron cores.
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Old 26th April 2004, 11:17 PM   #56
Magura is offline Magura  Denmark
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Picked up 45 kilograms of 1.9mm magnet wire yesterday

I guess I'll have some fun making the bobbins and even more when actually winding the inductors....will have to run 2 paralel wires to make them work as centertapped...again according to NP.

For now the biggest challenge is though to make a huge bobbin that is re-useable.

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Old 1st September 2004, 07:32 PM   #57
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Default ok here goes:

my plan:

source follower with 1:1 transformer as load...

driver is an ECC99 into either a 2:1 or 1:1 ? IT.

question is how to couple the IT to the gate of the mosfet and have a bias network in there...

also want to have a high bandwidth....

should I stick with the 28vdc on the mosfet.. at 3-4A bias?

probably use IRFP240N...

Have some 68,000uf caps for output... just get a choke for a CLC power supply...

probably a LC supply for ECC99 with a VR tube for regulation.

any problems with this???
ideas or things to improve it?

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Old 2nd September 2004, 03:42 AM   #58
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Hi, All,
I'm very intersted in Choke loading. Or common CT double choke, like ZEN V-7T. It makes unique, nice sound.
But where's the cct that is discussed all this time? No cct to see?
Is Circlotron's choke amp has been discussed somewhere?
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