ferrite rod material for GG filament choke

[KM1H]

61 mix is no good unless its for CB or 6M.

Coming from no less an amplifier guru than KM1H, this took the wind out of me.

I've always used 61 material for directly-heated filament chokes in the few linear amplifiers I've built or modified, from 160 through 10 meters. 61 Mix is also the choice of Amidon Associates.

But coming from Carl, what can I say? :-)

I suggest doing a bit of winding, measuring, and calculating Mike and determine the reactance on 160 & 80. I back up calculations with a SA or VNA to make sure nothing funny is going on.

As far as Amidons charts or whatever there is a huge difference between using a ferrite mix in a reasonant circuit and as a choke.

Just because it works for you means little if your dumping part of the drive into the choke bypass caps and filament transformer. OTOH it could be a good thing for those who like to overdrive their amps

So besides liking to follow me around what is a slopbucket man doing on this forum?

Carl

[W4AMV]

Type 43, ui:850,  2 inch toroid is what I have in hand. Will try that first.

A neat closing line on this is:

In GOD we trust, all others bring data.  

[KM1H]

Type 43 is good down to 1 MHz. Type 31 covers down to 500kHz. Either one should work for this

The problem....sometimes....when using a lower mu ferrite is that you have to add many more turns to get the same inductance as a higher mu mix. In some cases it works OK. Other times all the extra interwinding capacitance can/may create nasty resonances or otherwise degrade the choking effect. When its just a choke and not a tuned circuit I like to use as few turns as possible and as mentioned earlier back it up with the SA or VNA to look for the nasties. A GDO can find the resonances.

I didnt read much about the Henry problem but Id suspect that a small toroid (about FT-140 size) used with 30A of filament current (2x 3-400Z/500Z) plus trying to stop RF is not a good approach. They do tend to be drive hogs when 160M models are involved. It might be fine with a pair of 811/572B, 813, or similar. The last filament choke toroid amp I worked on was a Johnson Thunderbolt II which became the Tempo 2000; 80-10 with 3-400Z's. It had its problems when it arrived but that circuit worked fine at 1200W out with an overkill 100W drive.

Speaking of not enough choking impedance, the Dentron Clipperton L and its similar family is another one that suffers on 160.

[W4AMV]

I also have mix 77 in a 2 inch size and this ui is 2000. However, the ui is frequency dependent and I'll need to measure both the 77 and 43 for the same length wire and see what the XL does with frequency. I have a VZM which is hand for these measurements. Thanks.

[W0BTU]

So besides liking to follow me around what is a slopbucket man doing on this forum?

Well, I'm not following anyone around.   Amfone.net seems to be a pretty special place. I just started reading some of the posts last month, and I see there's some good people here.

You might very well find me on AM someday. Since reading this forum, I'm again toying with the idea of two paralleled 833-C's on the lower HF bands, perhaps plate or cathode modulated by a single 833-C.

[KX5JT]

Yes, my Henry 2k4 had an original toroid filament choke.  On AM, I had experienced AC hum on the carrier.  I dug and poked and prodded and someone finally admitted that during a certain period of time, the toroid choke was wound improperly and some 2K4's were out there with the mistake.  On sideband, it wasn't much noticed.  On AM it became clear.

Those particular amplifiers had each filament lead wound SEPERATELY, one on each side of the toroid, not wound TOGETHER in a bifilar fashion.  I had one.

There is nothing inherently wrong with a filament choke on a toroid but it needs to be wound BIFILAR fashion, just like if it were on a rod.

John KX5JT

[W1VD]

When constructing chokes from 61 material be especially wary of resonances. Unlike other ferrite materials, inductors wound on 61 will often have Q's approaching 300. Inductors wound on other ferrite materials are lucky to achieve 1/5 of that - some considerably less.   

[WA1GFZ]

Jay,
I always load the choke with around 2K ohms of resistance. I've seen HF amplifiers take off in the VHF range due to a high Q resonance in the choke.
I do not know what material is in my Lou McCoy donated rod.

[W4AMV]

Thanks for the added data. I'll measure the 77 material and 43 material from 500 kHz-110 MHz and report what I find. The material set has ui which are frequency dependent and I'll be able to find the real and imanginary parts of the Z over that range. Ideally there will be no resonance loops! It will be bifilar (pairs of wire) and will probably be space wound between each turn about 1-2 x the diam of the wire.

Alan

[WA1GFZ]

I had to use #7 to handle 43 amps so couldn't afford spacing turns.

[W4AMV]

# 7 WoW. Here is a link to a very interesting article:

http://www.highfrequencyelectronics.com/ see this monthe issue it is free to download

The small signal response of ferrites and the author explores the saturation affect.

[W4AMV]

here are the results of one xmfr. This should work well from 160 M- 30 MHz. Even at 110 MHz the resulting Z is ~ 2 pF.

[KM1H]

The 77 mix is good stuff; I use the FT240-77 to solve most noise problems from household devices.

[K5UJ]

I just got back from WB9DNZ's QTH where he wound no. 10 enamel on a form to make a choke using that  7 1/2"  x 1/2" 33 mix rod.   I provided the wire, rod and the coil form, which was a bit less in diameter than the rod.  I figured the wire would "spring back" so I thought we would need a form just a tad narrower than the rod.  I kept the tension on the wire while he did the winding--I had the easy job.   I am hoping it will be enough for a pair 4x1 filaments but I may have to have another one. 

Here's what we discovered:  The no. 10 doesn't have anywhere near the spring back we expected.  The coil was real tight and it was therefore a b**ch getting the rod into the coil.   That is one hell of a filament choke.

[W2VW]

Speaking of not enough choking impedance, the Dentron Clipperton L and its similar family is another one that suffers on 160.

The inadequate grid choke protects the inadequate plate tank on 160.

[WU2D]

A filament choke is there to provide a high impedance between the RF driven filament and the filament transformer at the other end. Loss is what you want and 61 mix is no good unless its for CB or 6M.

For a 4 holer use the 7 1/2"  x 1/2" 33 mix or the 4" for 2 tubes.

The FC-25A and others are 33 mix.

I have both sizes here and plenty of enamel wire up to #10 (for big tubes), PM for pricing, etc.


Carl

Doesn't Don have a 4-holer out in back of the schoolhouse?

Here is a cool site:  http://www.stormwise.com/page26.htm

Mike WU2D

[KM1H]

Speaking of not enough choking impedance, the Dentron Clipperton L and its similar family is another one that suffers on 160.

The inadequate grid choke protects the inadequate plate tank on 160.

There is no grid choke in a Clipperton L and the tank circuit is an easy fix. With a bit of work the L can run 1200W out 160-10 with 100W of drive and the tubes showing no color.

[W2VW]

Duh. I meant to say filament choke.
Too much vacation.

[Steve - K4HX]

Too much vacation.

No such thing.

[W0BTU]

Too much vacation.

No such thing.

Agreed! I'd like to have two vacations a year: six months each. ;-)

[KM1H]

Im on a permanent vacation

[W4AMV]

For completeness, here is a pix of the filament xmfr ready for insertion. The Delron block is 3x3 inch. The 77 material is 2.5 inch diameter toroid not 2. There are 28 turns and I spaced them wider then I originally stated. This is not heavy gauge, 16AWG, however, I am at 4A, not 40A, so a BIG difference. Which leads me to believe that the ROD became popular because it would be a real chore to put # 10 on a torus!

Finally, the resonance is NOT that of the winding, but is induced by the measurement itself. Turns out, the voltmeter probe has about 2 pF of C in its clip on version. So to get a real measure... go to a GDO! If I have time, I will do that and see where this unit is actually resonant.

[AMroo]

I have a collection of ferrite core toriods that I have been able to use successfully as filament chokes.
I am aware of the various grades of ferrites and their frequencies of operation.

Powdered iron like wise is used in frequency bands indicated by their coloring.
I would like to know if I can use powdered iron cores and also when and were I can use them.
What are the general rules covering their use, is it some thing to do with the RF power they can handle?

[W4AMV]

I have a collection of ferrite core toriods that I have been able to use successfully as filament chokes.
I am aware of the various grades of ferrites and their frequencies of operation.

Powdered iron like wise is used in frequency bands indicated by their coloring.
I would like to know if I can use powdered iron cores and also when and were I can use them.
What are the general rules covering their use, is it some thing to do with the RF power they can handle?

Good questions! For starters, see this months issue of High Frequency Electronics, I posted the link a few notes earlier in this thread. There is an excellent article in there that should address your requests... its about 12 pages long so quite in depth.

[KM1H]

This should keep you out of trouble for a few days

http://www.micrometals.com/

And this for the ferrites

http://www.fair-rite.com/newfair/index.htm

For the uknown materials you need to wind some turns, measure the L and then attack the formulas to determine what its useful for. A lot of surplus powdered iron cores come out of switching supplies and other LF applications.

Carl