High Quality Filament Chokes...

Design and use of Chokes for PS, anode and filament use.
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JeffreyJ
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High Quality Filament Chokes...

Post by JeffreyJ »

ok.. so we like DHT's.. and therefore we need only signal on our filaments.. so how, man in black, do we achieve that?

I know that there are some cool cores in my package.. I also think that typical filament chokes should be high bandwidth as they have no turns... but here's the real question: Is there a way to grab surplus low voltage transformers that were meant to be used with solid state dreck and convert them to 75tl filament chokes?

Peace,
Me
dave slagle
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Post by dave slagle »

On first thought this idea could work, all that is needed is an airgap and a low enough DCR secondary. Further thought tells me the primary will be useless, so 1/2 your window will be filled with unused copper and given the currents in question, you need all the copper you can get.

Lets say you are in a pinch... nothing says you cannot simply try a 16A secondary for a pair of 75TL's and see what happens. Conventional thinking says the trannie has no gap so the core will saturate and the results will be useless. Reality tells us magnetic cores are digital but the bit depth is far greater than the 2 bits most people assume, so "saturation" is a very gradual behavior and not an on/off proposition as most assume.

Sure 16A of DC through an ungapped core will pin most of the domains, but "pinned" domains behave as air and can be considered as such so as you saturate a core you essentially add an airgap (and reduce core area). Worst case with the core 100% saturated, you end up with an air cored inductor and the DCR as your filter element. The degree of saturation should be easy enough to test by simply measuring the ripple with the "saturated secondary" and then replacing it with a resistor having the same value as the DCR. This should give you a good idea on how the device is operating.

The next logical step is to attempt to add an airgap. This means get out your butter knife and butcher the thing. You should be able to pry apart the lams and sacrifice a few to get the core apart to restack it with a butt gap. Due to the crude fit the butt gap will actually be much larger than expected and should represent a good second set of tests to see if you are going in the right direction (again testing by the ripple reduction in circut). Next various spacers can be added (shim stock or post-it notes) looking for the null in the ripple. When the null (low point) is found you can assess if the part fits the job.

After wrestling with the salvaged lams you might get the urge to try some virgin ones and for a few bucks (say $30) get enough lams to do 2 cores from the man in the brown truck. Do note i am not selling cores, you would have to call ram sales or mcelroy electronics and the $30 is a guess Stacking them will be a pleasure and a slight (and i mean slight) gain will be noted. The big gain will be in lack of aggrivation. If you are lucky enough to find some C-core trannies things may be a bit different.

i still do not suggest this approach since you have to remember that 1/2 your winding window is still occupied by the unused primary winding. we could get into some wacky offset or feedback uses, but that is for another day.

So where do we go from here?

Since i am all about DIY, participation and learning I think i can offer up affordable gap it yourself filament and PS choke kits. Essentially you will get a box with a wound bobbin a core and some mounting hardware. Then it is up to you to determining the best gap in circuit and deal with the cosmetic and environmental issues.

dave
JeffreyJ
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thanks, Dave...

Post by JeffreyJ »

I will certainly have to think about this.. it is not as easy as I would have hoped..

it is possible that even throwing half the wire out (the primary) that we could still beat ordering proper iron, at least in the finance department.. but I suspect it is not really worth the hassle.. maybe I will just pry open and regap some of the useless iron that is around here to see what is involved...

I guess I was more thinking that when we start to get into these high filament current tubes, that there has to be something from the solid state world that we can use..

more thought, and some fun destruction with iron..

Me
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