Tube Radio Forum - The friendliest radio forum on the net!
Would you like to react to this message? Create an account in a few clicks or log in to continue.

Litz wire knowledge

Go down

Litz wire knowledge Empty Litz wire knowledge

Post by Resistance is Futile on Sun Apr 05, 2009 7:37 pm

This is from my posting in ARF:
I ran across an repair article in one of my repair and troubleshooting books that I found interesting enough to pass on.
This took about 2-1/2 hours of typing. (WHEW) But I did it for you all guys.

NOTE: This is reproduced (and edited) from RADIO troubleshooters HANDBOOK-3rd ed -A. GHIRARDI

“LITZ” WIRE SIZE, WIEIGHT AND DATA CHART

Since higher Q’s mean better selectivity and greater “gain”, r-f and I-f coils are designed to secure the highest Q compatible with other practical construction and circuit factors. In r-f circuits the inductance of the tuning coil is fixed by the wavelength range to be covered and the size variable condenser to be used. For a given wavelength range and tuning condenser therefore, any increase in Q must be obtained by a reduction of the radio-frequency resistance of the coil.

“SKIN-EFFECT”

The r-f resistance of the coil includes the direct current resistance (ohmic resistance of the copper), and is greater than it because of skin effect and because of losses that occur in the coil materials which are located in the rapidly alternating magnetic field of the coil. The skin effect is due to the tendency of the high-frequency alternating current to flow through a comparatively thin shell of the outside surface of the wire rather than uniformly through the whole cross-section area of the copper. Since this thin outside shell has comparatively little cross-sectional, it naturally offers a higher resistance to the flow of current than would be the case if the entire cross-section area were being used. The net result on the resistance offered by the wire to the flow of current through it is precisely the same as though a smaller wire were used.

What “Litz” Wire Is

Now the d-c resistance of a coil of winding can be decreased by using larger wire (but such increase is usually restricted by limitations regarding the allowable physical size of the coil). The “skin effect” of a coil winding may be decreased by increasing the total surface area of the wire. In order to increase the surface area without increasing the cross-section of the copper used, the conductor is sub-divided into as many individual strands as is economical and practical, insulating each strand individually from the next by a thin enamel coating. Commercial wire in this form is known as “Litzendraht” (commonly called “Litz” wire). Litz wire consists of many strands of fine wire, each stand individually insulated with enamel, and the group of wires covered with some protective textile insulation such as cotton or silk (although sometimes enamel, paper or other covering is used over the group of wires).

Because the total sum of the cross-section areas of the conducting outer shells of the many individual small conductors in litz wire is greater than would be the cross-sectional area of the larger, thin conducting outer shell of a single solid wire composed of the same total amount of copper, the litz wire has a smaller skin-effect (lower “skin resistance”) than the solid wire. For this reason, it has greater high-frequency conducting efficiency and is used in r-f coil windings where higher Qs are desired.

Why Individual Strands Of Litz Wire Should Be Twisted

“Skin-effect” Losses in the conductors of which r-f and I-f coils are wound have dictated the use of Litz wire wherever economically possible. However “skin-effect” goes a step further and requires that conductor not only be subdivided into multiplicity of individually insulated strands but that these strands be arranged in such a manner that each occupies a place on the surface of the conductor an equal per cent of the time so that the total r-f current will divide equally among the many strands and thereby give the lowest effective r-f resistance. Originally, the strands in Litz wire were braided in a certain manner to get this effect. Because of price, however, modern Litz wire as used in radio receivers is merely twisted so as to bring the different strands to to the surface at different points, giving a result approaching that of braided Litz, but at far less expense. Where Litz wire is made without twisting (that is, with parallel strands) the results are inferior to twisted Litz on two counts: (1) the losses are consistently higher than for twisted Litz; (2) coils made of it exhibit greater variations in resistance than coils made from twisted Litz.

How to solder Litz wire

Now that the use of Litz wire has become general both for r-f and I-f coils even in the cheaper radio receivers, it frequently becomes necessary for service men to solder the ends of such coils to terminals, etc. When soldering Litz wire, it is important that good permanent electrical contact be made to each and every strand of the wire otherwise some of the strands will not be conducting their share of the current and consequentially the r-f resistance will increase greatly.

It is evident, of course, that the insulating enamel must be cleaned off the end of each and every one of the fine strands of the Litz wire—without breaking any of them---before attempting to apply solder. This is apt to be very laborious and time-consuming work if an attempt is made to scrape each strand individually with sandpaper, or knife. A much simpler and quicker way—the one used in mass radio production--- is to hold the end of the wire for a second or two in the flame of an alcohol lamp and dip it, red hot, straight into a bath of alcohol. This operation completely removes the enamel insulation from the individual strands, baring the ends and leaving them so clean that they may be easily soldered._________________
Tubes, have something to glow about!
Formerly Smokinradios
KC7FXX Ham and GROL Licensed
Resistance is Futile
Resistance is Futile
Member
Member

Number of posts : 912
Registration date : 2008-03-12

Back to top Go down

Litz wire knowledge Empty Re: Litz wire knowledge

Post by tube radio on Sun Apr 05, 2009 11:52 pm

Thanks for the information

Lee

tube radio
Member
Member

Number of posts : 162
Age : 80
Registration date : 2008-07-24

Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum