Don

Most , if not all, power transformers we use in radios are close to half a volt-per-turn in any winding, primary or secondary.?My guess is 40 VA to 100 VA is almost the same for all receivers ?= same core X-C, so needs same turns per volt but the HT-37 takes ?100 VA? just for 6.3 and 5V so ?? maybe Halden can look into it? ==? =? ??240 turns would be about right for a 120 volt primary.?? I don’t recall opening one up and counting turns, let alone rebuilding one, but did you count them on a bunch??????? ?Since the transformer secondaries are all open circuit, the only power drawn form the AC line is what is needed to generate the magnetic lines of force aka flux in the transformer's core.??

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This changing flux generated by the primary winding also cuts the primary winding in such a way to generate a voltage to oppose the AC line voltage aka a counter EMF.? So in the end, only a miniscule current flows from the AC line through the primary winding.? Just enough line current flows to support the flux needed to generate the counter EMF and account for the power losses in copper and iron.? This counter EMF is in anything with a winding which gets it power form the AC line: transformers, relays, motors, inductors, whatever.

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It should be easy for you to verify the turns-per-volt of any power transformer.? All one needs is some thin magnet wire to wind around the core and something to measure the resulting voltage.?I don’t know that your wording is complete, but ya ..If only my fingers could feel that little wire. And then what would I do with that information? But it would be good to know if you are going to use a core for to build a new transformer. Note, you can have nothing smaller then a half turn coil.?? I don’t know how to make a half turn that does anything, but it you have half ?a turn or a quarter? or whatever, and connect a meter somehow as far as the core is concerned you end up with a circuit that is no turn or 1 turn , and …you need twisted leads all the way to the ?“half turn”, but then the leads have to go ? turn left and a ? turn right forming the rest of 1 turn, or maybe no turn.???? Like what is used in a Weller soldering gun heating element winding. The tip might be half a circle, but the other ? circle is around ?the core making one turn in all. ???However they do make half turns etc for instrument transformers by “drilling” a hole in the core so that this turn sees only ? of the total flux; this part turn is just to get the exact voltage ratio that they want. Now that we have been switched onto another siding, I don’t know why we are sitting here. ?

Jim –

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This was your final statement to the dissertation you wrote that was not needed: “So the magnetization in the inductor happens at the speed of light just as the charge does on the surface of the wire.? Like I said, mind blowing!” Enough from here. Regards – Mike

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Jim –

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Seems you have a tendency to make things more difficult than need be. The problem is that no electrical physical element is pure. You have inherent resistance of the wire and distributive capacitance between winding. Of course the opposite is true for an capacitor. You have ESR and you have inductance, the amount of which is dependent on the capacitor type. Also, other than an EM wave, nothing travels at the speed of light. Capacitors and inductors both have a time constant associated with them. Nothing is instantaneous. As I said, at T=0 and inductor is open and a capacitor is a short. – Mike

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Hi Jim – While in most transformers it is minimal, the primary resistance also draws current, so it is the sum of the two for total. Actually, the R might dampen the input surge some. Remember, at T equal to zero, only the R is present as the inductance is an open circuit until magnetization takes place. 73 – Mike

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Jim ??Without going back I believe ?WAS ?talking about Halden's measurements of the HT-37 power transformer

A question for you:

If a transformer has about 240 turns of wire in the primary which amounts to perhaps 5 ohms of resistance, how much current will it draw when connected to 120 volts, 60 cycles with all secondaries open circuit?? ?

JIM absolutely no idea unless at least you say what voltage it was designed for. Assuming it was designed for 120/60Hz we still don’t know. It all depends on the core steel itself ?and the physical sizes. Given the same steel? and sizes of laminations ?it now ?depends on how many laminations and ?how hard they decide to push the steel up the B-H curve [ not too too much saturation] at designed voltage. ?The ohms ?have little to do with it until the transformer is loaded.? It seems to me if you reduce the turns, you have to increase the core X-C area etc etc.. but if you make a desirable transformer the magnetizing current will be less than say 30% but that is loose. Since 1870’s the DOE mandated lower more efficient transformers [ for really big transformers] so core loss became critical and they finally started ?research etc and making high cost Grain oriented electrical Steel which? so now maybe all new transformers are more efficient than before.

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If it were connected to DC, the current would be perhaps 24 amps but when connected to 60 cycles AC, what would you expect the primary winding current to be and why? On DC ?input, ?normal transformers are useless, they go straight into saturation. like what happens during Goemagnetic storms and long lines between transformers, I think the rest is up above.? If I understand your questions. Getting late so my wording might be off, typoes too. Hope that this is readable

Halden, more good work! My comments in green, all yours still in black

Refs ???/g/HallicraftersRadios/message/30775

?From: [email protected] [mailto:[email protected]] On Behalf Of HF via groups.io
Sent: Thursday, August 8, 2024 3:09 AM ??

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Halden,? re? your post /g/HallicraftersRadios/message/30745 ?????

this has lingered on here and is now very late, and perhaps much is irrelevant, so don’t reply needlessly.

But take a look at “13 becomes 19”

your original remains black; ?My response in Green,

Re Intent: it's to load the transformer to simulate STBY operation.? ?

It is not to simulate a heavy startup load that relaxes as the heaters warm up.? ??…I’m not sure I understand this.

Its fine, and normal simulate STBY load, but when using a low source voltage the transformer inrush current due to saturation? will be very minimal and as others have said, at this low voltage the transformer runs with nowhere near normal flux, so it will not draw the normal AC inrush? current, which would begin to skyrocket if you were using up near normal line voltage.. all depending on very hidden details of this transformer.? As an extreme, remember if/when the transformer really saturates, only the primary resistance limits the current, but we hope/ expect that is not the case here.??

As an aside, in my way of thinking, inrush is a fairly loose term, even when dealing just with transformers, so if one wants to say much, you have to look at the details. In my mind inrush is usually spoken in terms of AC inrush and DC offset, rather than +/- peaks

the images show? very little in, which is expected at this low voltage?

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My search for voltage spikes is to understand how such a spike could occur during turn-off or turn-on because such a spike is probably what would cause insulation failure inside the transformer.? …That is a worthwhile exercise that is rarely spoken about, but to do it and make much sense of it, the switching characteristics of the switch have to be known; if it is an ideal switch it is simple; but if it has contact bounce then what are the mechanical details of the bounce: little bounce? big bounce?, frequency? Etc? and then what kind of voltage and current is it making and maybe breaking? Part of the answer is maybe? it is closing onto a very small voltage 99% resistive circuit, so it? will pass every little bounce as separate breaks[ a problem in low power logic circuits], but if the load is say a magnetic coil relay there is a good chance that the energy in the first closure will be enough that the “bounce open” is not seen as a? loss of conduction so these seemingly? very quick changes in conductance? don’t materialize into bouncing relay flux but slows down the rise a bit, and if the load is a transformer. My suggestion is primarily that any inductance will mean that there will be some arcing [resistance] in the contacts as they bounce open so, depending on all these details, and the higher frequency characteristics of the transformer, transient voltage spikes, may or may not be sizable.??

?It’s too bad that Galvani or Volta did not invent/ patent the “two-wireS ?switch” so we would understand them better. Switches are still at the bottom of any curriculum?

Yes, still 31 VAC.? Line voltage here is 120 so it's a little more than a quarter of line voltage. ……Thanks

Anticipated?? No.? I did notice something like this on earlier trials but didn't record my observations.? So I did them again to be sure. ?I thought you previously spoke of remanent flux altering the waveform; that was what I was meaning.? ?

Normally:? What I meant was that in this case the primary current is the same in the first few cycles as it is thereafter. Ok,???? ?

Image numbers.? Each image is marked with a filename TEK00nn.jpeg in the lower right corner.? I don't see a 13 in that set. ?Again, in order I see 14, 13 – 17, 27 – 63 , and now with glasses on, the 13 becomes 19. .? oh yore right sorry Halden!

Anticipated again?? Actually not.? I had the sense that the remanence might affect several cycles and that regardless of the polarity of the remanence, there would be a bit of extra current.? I didn't anticipate that the extra current would depend on the polarity of the first cycle or that it would be zero if that first cycle had one polarity or the other relative to the last cycle before turn-off. ?…As I see it and I thought you saw it, depending? largely on the polarity? of the last cycle before turn off and I guess more details the magnetism/flux? might be? north or south [plus or minus]? when you next turn it on.? So at turn on?? you might drive it thru zero to the other direction? or you might increase the flux in the same direction where you might see a bit of “saturation”? Your work has made me look into this, and the more I look the more complicated it gets, so don’t hang your hat on my words.? And as a simple aside, on a typical simple transformer the straight? sections all act the same , but at the corners all the horses want to take the inside lane, so the flux in the inside steel saturates well before everything else so even if the steel had a sharp saturation curve, the corners will soften the curve for the whole transformer. So now by one definition, the remanence of the steel is a fixed quantity,? but the actual flux remaining? at various spots on the 90 degree corner alter the simple ideas. I say this primarily because? the people that work on this seem to have a tough time cornering much of this… and that is just my take-away from reading.? I certainly would not want to try? to predict how much flux is left in the transformer , but if only one winding is connected I tend to agree if the last excursion? is a complete half cycle of current [as with an SSR] the core should be left? with a somewhat unknown hefty flux of known polarity. But if a mechanical switch turns it off, It might burn energy, and then stop conducting at zero current, but it might break the current, forcing sizable transients in parasitic elements. I wish I knew more about this, all I got is more questions.?

"Inrush"?? I usually associate inrush current as that used to fill up capacitors, warm up a light bulb filament, or warm up tube filaments.? So I was reluctant to call the extra current shown on the 'scope as "inrush".? So I wrote "surge".? I guess

they're really synonyms.? I don't know if there's a difference in common usage.? ….Yes, I the same word is used for many things. I understood that your use of “surge” for a transformer only was “transformer inrush” to me.?????????? Now If in general we speak of inrush or surge to a HT-37 or almost any tube radio, there is a surge on the transformer on energization and perhaps separately as heater/filament warm-up and soon due cap charging and draw on B+ and B++? that all affect the current profile on the primary,? so details are needed, but often forgotten; left to assumptions, maybe confusion. When speaking of energizing a transformer, in my world, inrush? is distinct from surge,? which might mean a high speed? lightning surge, maybe a high speed? power surge etc etc? so clarification is needed, but transformer inrush narrows things a lot

Thanks for marking up image 63.? Yes, in this case one can see both additional AC current inrush? AND a DC offset? .? I just happened to kook at 63, as I recall the one before it might even have more DC offset.? As I see it the DC offset is a result largely of the angle of closure [if the core has been demagnetized], while the AC inrush is due to core saturation? ,,which is often? the RMS value of the peak to peak after the DC offset is removed.. but there must be a better definition out there, but it is too long.

BTW, both 'scope channels are in DC mode, so these offsets are real, not artifacts of DC blocking capacitors. I assumed that.

Primary current vs. magnetization.? I think I used the term "magnetization" incorrectly.? What I meant to consider is the relationship between the current flowing in the primary and the amount of current that would cause core saturation. That sounds close to me but? I don’t think we want to normally hit real saturation or even close to any real saturation, but it is understood that? turn on often drives any practical transformers into saturation? Without looking back in my world "magnetization" is a very general term but? "magnetizing? current" of a transformer is the current which can be seen when there is no load on the transformer, so it just magnetizes the steel up and down drawing reactive current as Jim said, plus some real non-linear current caused by hysteresis, which we hope is low, but escalates quickly if it starts with higher? AC voltage, but we HOPE there is not too much saturation/hysteresis at rated voltage

I assumed that the amount of magnetic field was proportional to the current, not a combination of current and voltage.? Upon further thought, I see the argument that the magnetic field needs to be proportional to the product of current and voltage because the change in that field is what transforms the power from input to output, and power is voltage times current (times cosine of the phase difference if there is one).??? Maybe I threw you off? ???If you can look at an inductor or UNLOADED transformer?? in the way Jim mentioned, we just see the reactive[90 degree] current [magnetizing current, but if it is a transformer AND YOU LOAD it the secondary? also produces A-T [ampere-turns] trying to create flux, but the primary instantly responds by drawing more current and producing AT that? neutralize the tendency of the secondary to change the common flux? Once loaded, a good transformer? reflects a load that dwarfs the magnetization current, so the simple model of a transformer changes drastically as you go from no load to loaded. ???I like to look at an unknown transformer buy running it up on a variac, and hopefully noting a very low current, that increases a little with voltage, and then watching it rise quickly as it begins to saturate s somewhere near rated current, but hopefully the current at rated voltage is maybe 20%? current as a very loose number?????????? If this is the case, then in the intended circuit there would be twice the primary current and 4 times the primary voltage.? These measurements are at about 1/8 the power level of an HT-37 in STBY mode, not half.? I think I need to study the relationship between transformer current, magnetization, and flux some more.? … well.. I dunno

BTW, the load applied during this test is meant to draw current in the filament windings that's similar to the current flowing in the actual transmitter.? If I were to raise the input voltage by 4, I would raise the resistances by 4 also.?well.. I dunno? maybe later

Saturation under "normal start"??? .."normal start" is not very clear to me,? instead try?? turn the knob from “off to standby”???? OH maybe that means normal voltage? ? My understanding is that core saturation really needs to be avoided because when saturation occurs, energy turns into heat in the core.? Yes, it’s not desirable to run much into the saturation curve, but it is very hard to avoid some saturation largely due to economics and the fact that it is gradual increase as more steel is used. This relates to steady state operation; for “starting” the probability is that you will get saturation, and most SSR’s ensure it, and we have to pretty-much live with it.? ?When transmitting on 80m, my HT-37 draws 2.6A rms which is double the draw in STBY mode, which, in turn is approximately double the current used in my tests so far. ?I expect that the transformer is designed to not saturate during key-down transmit, and should have a bit of headroom even above that before it would saturate.? If the transition to core saturation is a function of current only, then I'm working at a quarter of that level or below.? I would say well?;?As above, when a transformer is running as a transformer at one voltage, the [AC ] flux barely changes with load current. The tendency of the secondary to create flux is instantly neutralized by the primary drawing more current and more A-T, neutralizing the secondary A-T? which share the core … it is the A-T that neutralize? so the flux in the common core never sees the load current.. All due to the continuous hi-permeability core.? That’s because the coupling is so tight almost like a gear box, or at least a very good old belt drive,?? ??

If the above is correct, the inrush current would have to be at least double the STBY operating current to enter saturation.? Do you agree?? For my next session, I might move the HT-37 to the 'scope's location to assess the actual starting current magnitude and how long it lasts.?? ?… ??? Maybe try rewording that,? or something? .

What do you mean by

…? likely cant reenergize transformer under full power?????? Reply? ….?? You/I can’t flip the switch off and “on” that fast or I would not try it,, but if you really mean???? MOX? + “rapid???? STBY-->OFF-->STBY? ?> MOX,?? ohh I dunno? perhaps I am missing something

I never thought that a mechanical switch would wait for current zero to break the circuit.? But on further thought, I see that it kindof does.? If the contacts separate while current flows, it draws an arc which means current is still flowing.? The arc does add some voltage drop to the circuit, so there's partial switch opening.? Then, when the voltage approaches zero, there isn't enough voltage to maintain the arc and current fully stops.? Yes, I may see this when I start watching what happens in the real transmitter. .. Something like that. ??If you have a resistive load there is no wait, but if there is inductance things are not so simple.? If you hold two wires feeding a light bulb together? and separate the wires the current will stop as soon as the metal contact is lost and has just a hair of a gap, at least enough for that normal voltage. But, If you stick a big choke in there instead it will fight to maintain current.? you will likely get a spark/arc, as the energy in the inductor has to go somewhere to get down to no current, so the inductor creates a voltage high enough to try to? maintain the current in an arc, and absorbs the energy; unless perhaps the voltage gets so high that it finds a better path wiping out some insulation. a big gap switch will draw a longer and longer arc at higher voltage before expected current zero at the expense of the insulation unless you design your “two-wires switch ”? well. This is my attempt to look at it, I have no references, and terms? In BIG circuit breakers all this is of very big concern.

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Halden, just a simple reply, while I try to finish old stuff

Respectfully Halden , I PRIMARILY USE email , I have no idea if right now if you are just making a comment to me, or you are relating to some specific message that I sent . I can’t see a clue as what you might be talking about, and I have other emails, gardens, weed and dust and bills to worry about so my brain is clogged up.

WE/I do need something, so we know what “you” are looking at; ?I can’t see your screen! ?usually a small snippet of near the top of the message gets us enough info to clue in, but us old guys, slow on the draw, can’t keep up to two young guys firing high speed text messages between themselves or to HOo NOSe HOO

While there is often a TO name, I believe this forum is to be for all members to understand and maybe learn somebody else’s ideas

But rarely do we need? to quote much, however some don’t agree.

SO, I attempt to reply using a reference that should help most members, future members or outsiders that are following, and in many cases i start with a name so others get an idea.

I do not usually show much previous stuff, and if I do I put it in that ?quoted text ? box? which clogs up emails but not on- line.

However if one does not put the references in ?TAB indent? ,, they end up in the message..OMG

Maybe I did do that by accident as forgetting the TAB indent? ,, and OOPS

Every body knows that images can gobble space, so I try not to? repeat them, but many images ?are spaced in text it becomes difficult to not repeat them

And perhaps my computer displays all this stuff?? in some old format.

Halden if the top sounds rather rough, it is not intended to be that, but I don’t know how to reword it. We see thru only one set of eyes, and at our own screen. I have a cousin who can barely see anything, and I have to assume that there are many others that have ?lesser difficulties but don’t tell us, and that many of us cant imagine what it is like for them. Oh how good are “you” on a unicycle? Or boxing ring or marathon? Soldering or maybe pottery or knitting, Said with good intent, but no gas in the tank.

Oh ya when you are on line, do you find it easy or hard? IF you do want to add a reference?? It did weird things to me.

PS Im sticking your message inside a TAB indent so it should go into the ?quoted text ?box ?on line

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Halden, I am sorry, about the missing reference. I usually leave at least part of the post I am speaking about.

I think you are right, but due to my failure I don’t have a reference either.

As an aside, I don’t see a reference in many of your posts either…. It is easy when using email [at least from here] and it used to be not to hard in GIO on-line

But for some time now the old method on GIO has not worked. I find that editing on—line is dangerous, at least for us big old fat finger types.

We need to leave some sort of reference. By ?the way when you are on line,? you can copy the whole link for the post number, but the ongoing gio is tricky.

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Floyd,

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I’m curious as to the type of capacitor that was replaced.? Hallicrafters often used the Cornell Dubilier “Tiny Chief” type in many of their products. ?These have a pink-0colored appearance with yellow stenciling.? They have a high failure rate today.

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Paul

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