Fuling said:
Hi,
Just download Audiotester V2. Download the .zip version from he download page NOT the installer version, the installer version didn’t install properly on my system. Hook-up a capacitor // to the coil and measure the impedance plot and resonance frequency with your audiocard. From the formula Fc = 1/(2 x pi x sqrt (L x C) ) you can find the inductance (L).
Cheers
Magura, you are a hero!!
Is that going to be air cored inductors?
I assume that since you ordered 40kg´s!
I too have vague plans for a real monster project.
It all started a week or so ago when I picked up some junk from a broken machine (WireEDM??) at my brothers job, including three huge heatsinks (approx. 6x16x80cm with fins on both sides)
and three transformers in the kilowatt range.
Unfortunately the transformers didn´t produce any voltages suitable for class A transistor amps, but I have some ideas about using them as chokes if I can cut some airgaps in the cores.
The wire is definitely thick enough to allow at least 5 A bias, probably more.
Though, I´m not sure about doing this since I think these transformers would be excellent as mains filters for my CDP
I also got some really big aircored inductors that should be fine for PSU filtering purposes. The wire is at least 3mm so current handling shouldn´t be a problem
Is that going to be air cored inductors?
I assume that since you ordered 40kg´s!
I too have vague plans for a real monster project.
It all started a week or so ago when I picked up some junk from a broken machine (WireEDM??) at my brothers job, including three huge heatsinks (approx. 6x16x80cm with fins on both sides)
and three transformers in the kilowatt range.
Unfortunately the transformers didn´t produce any voltages suitable for class A transistor amps, but I have some ideas about using them as chokes if I can cut some airgaps in the cores.
The wire is definitely thick enough to allow at least 5 A bias, probably more.
Though, I´m not sure about doing this since I think these transformers would be excellent as mains filters for my CDP
I also got some really big aircored inductors that should be fine for PSU filtering purposes. The wire is at least 3mm so current handling shouldn´t be a problem
Fuling said:
Yes, each inductor is ending up close to the 10Kg. mark.
I dont like the idea of playing with torriodals for inductor purposes as Nelson Pass have been recommending. After all, what is another few hundred $ in a project like that? Its allready waaaay out of line in all aspects, might as well go all the way
As for your trafos. Please drop me a line offline. I have some experience with rewinding trafos.
Magura
That´s going to be quite some inductors, Magura!!
I don´t think my transformers are good subjects for rewinding, the cores are well varnished and the windings are made without bobbins.
They look quite a bit like very big microwave-oven transformers, they even have the same kind of magnetic shunts (or whatever it´s called) between the windings. I guess I have to knock those out if I´m going to use them.
If I ever gets curious about OTL amps they might be perfect for the PSU since they put out about 105V each.
Two of them would be a great +-150V 2kVA supply
I don´t think my transformers are good subjects for rewinding, the cores are well varnished and the windings are made without bobbins.
They look quite a bit like very big microwave-oven transformers, they even have the same kind of magnetic shunts (or whatever it´s called) between the windings. I guess I have to knock those out if I´m going to use them.
If I ever gets curious about OTL amps they might be perfect for the PSU since they put out about 105V each.
Two of them would be a great +-150V 2kVA supply
Hi -
I found, through the limited research I've done, that there's a couple things worth noting about air core magnetics. If I'm wrong about any of this, please correct me.
One thing is that for a solenoid style aircore choke wound like the 'perfect lay' inductors, there's an optimal shape to get the maximum inductance per length of wire which corresponds closely to the proportions that Solen uses for theirs. For a 4" diameter coil, it would be 1" wide and 1" deep for the windings (square winding cross section). You can scale these proportions up or down in size, of course. Neatness counts during the winding process to get the most inductance for the least wire and smallest size. I've found that avoiding kinking the magnet wire in the process of winding helps here also.
The inductance value of an air core choke once its installed into a circuit, since it doesn't have a highly permeable core, can be somewhat more sensitive to the proximity of other magnetic materials or components that do have such cores to concentrate the magnetic flux lines, but this shouldn't be a significant effect if a few inches spacing is maintained.
When the inductor is wound and tested to satisfaction, I usually heat up some 5 minute epoxy to about 130F to make it super runny so as to permeate the windings better, then mix it and quickly pour it over the windings to 'pot' them. Warning: it sets up fast when this warm, usually within about a minute.
Air core transformers for audio are more problematic, since the magnetic coupling between windings tends to be significantly lower than when a permeable core is added, not a good thing for wideband transformer action. There may be ways around this by changing the geometry, but I've only wound one solenoid style air core auto transformer so far & don't know if I'll have any time to pursue it further.
I found, through the limited research I've done, that there's a couple things worth noting about air core magnetics. If I'm wrong about any of this, please correct me.
One thing is that for a solenoid style aircore choke wound like the 'perfect lay' inductors, there's an optimal shape to get the maximum inductance per length of wire which corresponds closely to the proportions that Solen uses for theirs. For a 4" diameter coil, it would be 1" wide and 1" deep for the windings (square winding cross section). You can scale these proportions up or down in size, of course. Neatness counts during the winding process to get the most inductance for the least wire and smallest size. I've found that avoiding kinking the magnet wire in the process of winding helps here also.
The inductance value of an air core choke once its installed into a circuit, since it doesn't have a highly permeable core, can be somewhat more sensitive to the proximity of other magnetic materials or components that do have such cores to concentrate the magnetic flux lines, but this shouldn't be a significant effect if a few inches spacing is maintained.
When the inductor is wound and tested to satisfaction, I usually heat up some 5 minute epoxy to about 130F to make it super runny so as to permeate the windings better, then mix it and quickly pour it over the windings to 'pot' them. Warning: it sets up fast when this warm, usually within about a minute.
Air core transformers for audio are more problematic, since the magnetic coupling between windings tends to be significantly lower than when a permeable core is added, not a good thing for wideband transformer action. There may be ways around this by changing the geometry, but I've only wound one solenoid style air core auto transformer so far & don't know if I'll have any time to pursue it further.
I have some doubts about Maguras idea about using air wound chokes in a Zen v7, since the article specifically calls for "coupled inductors".
In my world coupled inductors means two (in this case indentical) windings on the same core or one centertapped winding, but what happens when there is no core?
Not trying to spoil your fun here, Magura.
In my world coupled inductors means two (in this case indentical) windings on the same core or one centertapped winding, but what happens when there is no core?
Not trying to spoil your fun here, Magura.
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
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
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.
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.
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.
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.
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.
Magura
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.
Magura
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?
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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