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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Halden The second o'scope image is exactly what I would expect to see from an SSR switch at turn on.? At the voltage zero crossing, the current is always at a maximum with voltage leading the current by 90 degrees.? The initial buildup of the transformer's magnetic field requires a slug of current, more so if the transformer's core was left magnetized when the voltage was of the opposite polarity.? The SSR will always force this condition at every turn on.? This is the repeated transformer stress mentioned in previous posts.? The slug of current causes that thump heard as the transformer's primary coil tries to move in reaction to the very high start up current. What conditions are different in the third o'scope image?? This contradicts what is shown in the second image.? Would expect this to happen when measuring the E&I characteristics of a resistance, not a reactance. Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Thursday, August 8, 2024 at 04:51:23 AM CDT, HF via groups.io <incorridge@...> wrote:
(2nd post this evening)
This image shows the profile of primary current starting with a peak a little more than 4 A and decaying over about 4 seconds to about 1.6A as the filaments warm up.? In this case, there was no big current surge.
??
Next, I installed the Omron SSR in series with the original mechanical switch to see what happens when the transformer turns on at zero-crossing voltage and off at zero-crossing current (almost the same time as voltage zero-crossing).? Now that we have entire half cycles at the start and end, the surge current, when it occurs, is much stronger:
Yes, that's 49A!
These surges occur only when the last cycle before turn-off is of the same polarity as the first cycle after turn-on.? This is consistent with the explanation that remanence and saturation are the causes.? The core is left magnetized with one polarization when the transmitter is turned off, and the first cycle once turned on seeks to increase that magnetization further.? Since it hits the limit, there is no further conversion to magnetism available, so the current is limited only by the resistance in the primary, the current-sampling resistor, the wiring in the transmitter, and the wiring from the outlet to the circuit breaker panel.
Sometimes, there's no such surge and the measurement looks like this:
A few other notes:
I solved the problem with the images.? It doesn't have anything to do with groups.io.
The familiar THONGGGG! sound occurs when one of these big surges occurs.
Yes, Jim, the current and voltage are approximately in phase.? You are correct that in a purely reactive circuit they would be 90 degrees out of phase.? Evidently, a loaded transformer is not a purely reactive circuit.
I have not yet looked for voltage surges in the secondary and thus have not looked for possible correlation between such surges and different conditions in the primary.
This transmitter has certainly survived many turn-on surges in the 11-24 A range.? I'm reluctant to subject it to surges of twice that magnitude.? I'm concerned that if there's a nick in the primary winding, such surges might cause it to open.? At this point, it appears better to keep using the mechanical switch instead of installing a zero-crossing SSR to manage the transformer switching.?
But I'd prefer to never have any such surge at all.? To achieve this, I have designed a circuit to ensure that the first cycle is always of the opposite polarity of the last one the previous time the transmitter was on.? I need to order? (and receive)? a part, so it'll be a while before I report the results on that.
Cheers,
Halden VE7UTS
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Re: Riders Manuals
?
toggle quoted message
Show quoted text
The files are also posted here:
?
Same stuff but also the Index to locate which volume to find what you are
looking for:
?
Most of this stuff floating around ebay and the web was scanned back in the
90's so resolution of the pages and schematics is of analog quality.
Fortunately, I have all 23 volumes in real paper, including addendums,
updates, etc. and with a digital scanner/printer, the resolution is light years
better.
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Pete, wa2cwa
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On Wed, 07 Aug 2024 20:00:30 -0700 "Justin Bowser - KI5GKD" <justin.bowser@...>
writes:
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Don I was responding to what you said which is at the very bottom of this email. "Anyhow, Halden¡¯s current was about in-phase with the voltage [ I copied and shifted the current which is not perfectly symmetrical, but was not able come up with any shift ], so the load current was determining the ?primary current ?no matter how meaningless you think it is." There is no need to correct anything.? If anyone is still following this thread, the point has been made that there is a phase difference between I&E in a reactance.? In fact, this is the very meaning of the word "reactance."? ? But to see this clearly, both have to be measured at the same time and place.? Measuring I in one transformer winding and voltage in another will not show this special relationship. I look at this forum as a means to share knowledge about these fine radios.? I understand that some of us come to this forum without a solid understanding of component fundamentals and that is OK.? It is not really necessary to go into the technical weeds when one already realizes that old waxed paper & foil capacitors should be replaced, even before one applies AC power.? Tubes should be checked for emission and shorts and while cleaning the chassis, look for signs of damage.? Always check any fuses for the proper value! Just keep in mind that these radios were designed and built with an eye on cost.? The best components were too expensive to use.? That is not to say that hallicrafters radios did not perform well, they certainly did but comparisons have to be made with other radios in the same price class.? It should go without saying that a radio of the same era costing 10 times the price should perform better. One last thing, don't be afraid of challenging "common knowledge."? There is a lot out there that is considered "undeniable facts" but which falls apart when one takes a closer look. Back to fixing up nice old radios, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Wednesday, August 7, 2024 at 12:03:24 PM CDT, don Root <drootofallevil@...> wrote:
Hi Jim,? You are right about needing to get into the nitty-gritty! I don¡¯t understand why you wrote all this, but it¡¯s good to learn more, thanks. but at the end you said: ¡°If you can find a source that backs up ???¡.???? your claim that voltage and current are in phase in reactive circuits,¡¡..¡± I took a lot of time looking for that phrase in this thread even going back 100 postings, and even using Ctrl-F, and then even looking for a three word sequence, and I can find nothing in this topic. So, maybe I was sleepwalking when I posted it or sleepwalking when I deleted the posting. So please advise what the message number is, so I can edit it, correct it and apologize to members that I have deceived, all in the interest of group integrity. ? ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Tuesday, August 6, 2024 2:01 AM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? Don The transformer has many inventors, as you may know, if you have done any research on the subject.? Much of what was used to electrify Niagara Falls came from Europe since they were far ahead of Westinghouse in AC development at that time.? Tesla became a hindrance to Westinghouse in three phase power development.? Tesla's polyphase system is not the same as a three phase system.? But this is another story. ? Induction is the key to the operation of chokes, transformers, motors and anything else that uses a coil of wire.? A transformer is just two or more inductors that are magnetically coupled and share the same magnetic flux but the basic operation is the same as an inductor.?? ? In an inductor, as the magnetic flux builds, it cuts the same coil and produces a counter electromotive force (EMF) to oppose the current that is producing the magnetic flux.? If DC current is producing the magnetic flux, the flux will reach a maximum density since the steady state current cannot produce any more magnetic lines of force so induction stops.? If AC current is producing the magnetic flux, it again reaches a maximum but then changes direction and reverses back to zero current then changes the direction of the magnetic field to repeat the process with an negative current.? Induction does not stop when AC current is involved. ? So induction is producing a second current in the same coil to oppose the buildup of the magnetic field and force a constant current to flow.? If a second inductor also sees this same changing magnetic flux, a second EMF is produced in this second inductor.? If the number of turns in each inductor is the same, the same voltage and current appears in the second inductor.? Increasing the number of turns in the second inductor increases the voltage but reduces the current so the same power is available in the second inductor or winding.? Reducing the number of turns in the second inductor reduces the voltage but increases the current.? The power induced in the second inductor or winding is the same as that found in the first inductor or winding less any power loss in the wire and magnetic core. ? As for the voltage and current being in phase in inductive circuits, it is just not possible.? See: In part: "The phase difference between voltage and current in an AC (Alternating Current) circuit is due to the presence of reactive components, such as capacitors and inductors. In a purely resistive circuit, the voltage and current are in phase, meaning they reach their maximum and minimum values at the same time. However, in circuits with capacitive or inductive elements, the voltage and current exhibit a phase difference. In a capacitive circuit, the current leads the voltage by 90 degrees. This is because the capacitor opposes changes in voltage, causing the current to reach its maximum value before the voltage reaches its maximum. In an inductive circuit, the current lags the voltage by 90 degrees. This is because the inductor opposes changes in current, causing the voltage to reach its maximum value before the current reaches its maximum. The phase difference between voltage and current has important implications in the analysis and design of AC circuits, as it affects the power factor, which is the ratio of the real power to the apparent power. A phase difference other than 0 degrees results in a power factor less than 1, which can lead to inefficiencies in the circuit." There is more in the above article but this will suffice. ? I know that all of this is confusing and contradicts what you may have learned in tech school if you have had some formal training in electronics.? Shortcuts in explaining what happens in reactive circuits were made so as to cover as much ground as possible in a relatively short time of study. When you do a much deeper dive, you will find that these shortcut explanations no longer explain what is happening.? They just don't hold up.?? ? If you can find a source that backs up your claim that voltage and current are in phase in reactive circuits, please post the URL here, I would be interested in what it has to say. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy ? On Monday, August 5, 2024 at 09:40:06 PM CDT, don Root <drootofallevil@...> wrote: ? ? Thanks for responding Jim You could have a transformer with such bad steel that the magnetizing current dominates the reflected current from the load, but nobody wants one of those. I don¡¯t know if somehow we are talking past each other somehow bu Mr Faraday was working with induction coils ¡°When was the transformer invented? A: The property of induction was discovered in the 1830's but it wasn't until 1886 that , working for Westinghouse built the first reliable commercial transformer.¡± ? Anyhow, Halden¡¯s current was about in-phase with the voltage [ I copied and shifted the current which is not perfectly symmetrical, but was not able come up with any shift ], so the load current was determining the ?primary current ?no matter how meaningless you think it is. ? -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýHi Jim,? You are right about needing to get into the nitty-gritty! I don¡¯t understand why you wrote all this, but it¡¯s good to learn more, thanks. but at the end you said: ¡°If you can find a source that backs up ???¡.???? your claim that voltage and current are in phase in reactive circuits,¡¡..¡± I took a lot of time looking for that phrase in this thread even going back 100 postings, and even using Ctrl-F, and then even looking for a three word sequence, and I can find nothing in this topic. So, maybe I was sleepwalking when I posted it or sleepwalking when I deleted the posting. So please advise what the message number is, so I can edit it, correct it and apologize to members that I have deceived, all in the interest of group integrity. ? ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Tuesday, August 6, 2024 2:01 AM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? Don The transformer has many inventors, as you may know, if you have done any research on the subject.? Much of what was used to electrify Niagara Falls came from Europe since they were far ahead of Westinghouse in AC development at that time.? Tesla became a hindrance to Westinghouse in three phase power development.? Tesla's polyphase system is not the same as a three phase system.? But this is another story. ? Induction is the key to the operation of chokes, transformers, motors and anything else that uses a coil of wire.? A transformer is just two or more inductors that are magnetically coupled and share the same magnetic flux but the basic operation is the same as an inductor.?? ? In an inductor, as the magnetic flux builds, it cuts the same coil and produces a counter electromotive force (EMF) to oppose the current that is producing the magnetic flux.? If DC current is producing the magnetic flux, the flux will reach a maximum density since the steady state current cannot produce any more magnetic lines of force so induction stops.? If AC current is producing the magnetic flux, it again reaches a maximum but then changes direction and reverses back to zero current then changes the direction of the magnetic field to repeat the process with an negative current.? Induction does not stop when AC current is involved. ? So induction is producing a second current in the same coil to oppose the buildup of the magnetic field and force a constant current to flow.? If a second inductor also sees this same changing magnetic flux, a second EMF is produced in this second inductor.? If the number of turns in each inductor is the same, the same voltage and current appears in the second inductor.? Increasing the number of turns in the second inductor increases the voltage but reduces the current so the same power is available in the second inductor or winding.? Reducing the number of turns in the second inductor reduces the voltage but increases the current.? The power induced in the second inductor or winding is the same as that found in the first inductor or winding less any power loss in the wire and magnetic core. ? As for the voltage and current being in phase in inductive circuits, it is just not possible.? See: In part: "The phase difference between voltage and current in an AC (Alternating Current) circuit is due to the presence of reactive components, such as capacitors and inductors. In a purely resistive circuit, the voltage and current are in phase, meaning they reach their maximum and minimum values at the same time. However, in circuits with capacitive or inductive elements, the voltage and current exhibit a phase difference. In a capacitive circuit, the current leads the voltage by 90 degrees. This is because the capacitor opposes changes in voltage, causing the current to reach its maximum value before the voltage reaches its maximum. In an inductive circuit, the current lags the voltage by 90 degrees. This is because the inductor opposes changes in current, causing the voltage to reach its maximum value before the current reaches its maximum. The phase difference between voltage and current has important implications in the analysis and design of AC circuits, as it affects the power factor, which is the ratio of the real power to the apparent power. A phase difference other than 0 degrees results in a power factor less than 1, which can lead to inefficiencies in the circuit." There is more in the above article but this will suffice. ? I know that all of this is confusing and contradicts what you may have learned in tech school if you have had some formal training in electronics.? Shortcuts in explaining what happens in reactive circuits were made so as to cover as much ground as possible in a relatively short time of study. When you do a much deeper dive, you will find that these shortcut explanations no longer explain what is happening.? They just don't hold up.?? ? If you can find a source that backs up your claim that voltage and current are in phase in reactive circuits, please post the URL here, I would be interested in what it has to say. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy ? On Monday, August 5, 2024 at 09:40:06 PM CDT, don Root <drootofallevil@...> wrote: ? ? Thanks for responding Jim You could have a transformer with such bad steel that the magnetizing current dominates the reflected current from the load, but nobody wants one of those. I don¡¯t know if somehow we are talking past each other somehow bu Mr Faraday was working with induction coils ¡°When was the transformer invented? A: The property of induction was discovered in the 1830's but it wasn't until 1886 that , working for Westinghouse built the first reliable commercial transformer.¡± ? Anyhow, Halden¡¯s current was about in-phase with the voltage [ I copied and shifted the current which is not perfectly symmetrical, but was not able come up with any shift ], so the load current was determining the ?primary current ?no matter how meaningless you think it is. ? -- don??? va3drl |
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Re: Halicrafters SX17 transformer
Yes, see message # 30485 "Further investigation revealed that the primary of transformer T5 is open." Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Wednesday, August 7, 2024 at 07:16:06 AM CDT, Joe Connor via groups.io <joeconnor53@...> wrote:
I want to make sure I understand this. Was the Hammond 124A used to replace the interstage transformer?? ? ? ? ? ? ? ? ? ? ? ? ?Joe Connor
On Tuesday, August 6, 2024 at 03:03:10 PM EDT, Jim Whartenby via groups.io <old_radio@...> wrote:
John I figured that Richard would chime in about your audio power comment.?? 18 watts sounds to the normal ear as twice as loud as that from a 1.8 watt amplifier.? The SX-17 manual mentions that the audio amp puts out 13 watts of "undistorted" audio, whatever that meant before 'hi-fi" became popular.? In any event, if you are just going to listen to speech you may not notice much difference but music or singing might be a different story.?? The reserve power might make the listening experience a bit more life-like especially if your speaker response is pretty flat across the audio spectrum.? Again, the smallest change the normal ear can perceive is 3dB or twice the power.? The difference in performance between a 3 ohm speaker and a 4 ohm speaker is not worth the worry.? The more efficient the speaker is, the louder it will sound.?? I use an old Zenith wood cased bookshelf speaker from a thrift shop with an added 70 volt line transformer using the 10 watt tap.? This is enough to convert the headphone 600 ohm output of a military type radio to the 8 ohms needed by the speaker.? I believe the audio power of the amplifier inside the radio is under half a watt maximum but it sounds just fine for speech! Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, August 6, 2024 at 12:16:17 PM CDT, John via groups.io <siloam@...> wrote:
In the end purchasing a new transformer proved to be necessary. The Hammond 124A appears to be working just fine although I doubt that the set is currently putting out anywhere near 18W. After fixing problems in the decoder and IF section (mostly caused by leaky paper wax capacitors that had to be replaced, the set sprang into life and started receiving stations. I implemented an arrangement similar to Franz (HB9HPZ) - so thank you for posting that. I am using a temporary speaker setup which is nowhere near ideal, and perhaps not correctly matched but good enough to test with and I can get good and clear volume from the set, but it does have to be turned up over halfway, maybe two thirds of the way. In any case, it is working so thanks for the comments with advice regarding the transformer.
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Re: Halicrafters SX17 transformer
John I figured that Richard would chime in about your audio power comment.?? 18 watts sounds to the normal ear as twice as loud as that from a 1.8 watt amplifier.? The SX-17 manual mentions that the audio amp puts out 13 watts of "undistorted" audio, whatever that meant before 'hi-fi" became popular.? In any event, if you are just going to listen to speech you may not notice much difference but music or singing might be a different story.?? The reserve power might make the listening experience a bit more life-like especially if your speaker response is pretty flat across the audio spectrum.? Again, the smallest change the normal ear can perceive is 3dB or twice the power.? The difference in performance between a 3 ohm speaker and a 4 ohm speaker is not worth the worry.? The more efficient the speaker is, the louder it will sound.?? I use an old Zenith wood cased bookshelf speaker from a thrift shop with an added 70 volt line transformer using the 10 watt tap.? This is enough to convert the headphone 600 ohm output of a military type radio to the 8 ohms needed by the speaker.? I believe the audio power of the amplifier inside the radio is under half a watt maximum but it sounds just fine for speech! Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, August 6, 2024 at 12:16:17 PM CDT, John via groups.io <siloam@...> wrote:
In the end purchasing a new transformer proved to be necessary. The Hammond 124A appears to be working just fine although I doubt that the set is currently putting out anywhere near 18W. After fixing problems in the decoder and IF section (mostly caused by leaky paper wax capacitors that had to be replaced, the set sprang into life and started receiving stations. I implemented an arrangement similar to Franz (HB9HPZ) - so thank you for posting that. I am using a temporary speaker setup which is nowhere near ideal, and perhaps not correctly matched but good enough to test with and I can get good and clear volume from the set, but it does have to be turned up over halfway, maybe two thirds of the way. In any case, it is working so thanks for the comments with advice regarding the transformer.
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Don The transformer has many inventors, as you may know, if you have done any research on the subject.? Much of what was used to electrify Niagara Falls came from Europe since they were far ahead of Westinghouse in AC development at that time.? Tesla became a hindrance to Westinghouse in three phase power development.? Tesla's polyphase system is not the same as a three phase system.? But this is another story. Induction is the key to the operation of chokes, transformers, motors and anything else that uses a coil of wire.? A transformer is just two or more inductors that are magnetically coupled and share the same magnetic flux but the basic operation is the same as an inductor.?? In an inductor, as the magnetic flux builds, it cuts the same coil and produces a counter electromotive force (EMF) to oppose the current that is producing the magnetic flux.? If DC current is producing the magnetic flux, the flux will reach a maximum density since the steady state current cannot produce any more magnetic lines of force so induction stops.? If AC current is producing the magnetic flux, it again reaches a maximum but then changes direction and reverses back to zero current then changes the direction of the magnetic field to repeat the process with an negative current.? Induction does not stop when AC current is involved. So induction is producing a second current in the same coil to oppose the buildup of the magnetic field and force a constant current to flow.? If a second inductor also sees this same changing magnetic flux, a second EMF is produced in this second inductor.? If the number of turns in each inductor is the same, the same voltage and current appears in the second inductor.? Increasing the number of turns in the second inductor increases the voltage but reduces the current so the same power is available in the second inductor or winding.? Reducing the number of turns in the second inductor reduces the voltage but increases the current.? The power induced in the second inductor or winding is the same as that found in the first inductor or winding less any power loss in the wire and magnetic core. As for the voltage and current being in phase in inductive circuits, it is just not possible.? See: In part: "The phase difference between voltage and current in an AC (Alternating Current) circuit is due to the presence of reactive components, such as capacitors and inductors. In a purely resistive circuit, the voltage and current are in phase, meaning they reach their maximum and minimum values at the same time. However, in circuits with capacitive or inductive elements, the voltage and current exhibit a phase difference. In a capacitive circuit, the current leads the voltage by 90 degrees. This is because the capacitor opposes changes in voltage, causing the current to reach its maximum value before the voltage reaches its maximum. In an inductive circuit, the current lags the voltage by 90 degrees. This is because the inductor opposes changes in current, causing the voltage to reach its maximum value before the current reaches its maximum. The phase difference between voltage and current has important implications in the analysis and design of AC circuits, as it affects the power factor, which is the ratio of the real power to the apparent power. A phase difference other than 0 degrees results in a power factor less than 1, which can lead to inefficiencies in the circuit." There is more in the above article but this will suffice. I know that all of this is confusing and contradicts what you may have learned in tech school if you have had some formal training in electronics.? Shortcuts in explaining what happens in reactive circuits were made so as to cover as much ground as possible in a relatively short time of study. When you do a much deeper dive, you will find that these shortcut explanations no longer explain what is happening.? They just don't hold up.?? If you can find a source that backs up your claim that voltage and current are in phase in reactive circuits, please post the URL here, I would be interested in what it has to say. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Monday, August 5, 2024 at 09:40:06 PM CDT, don Root <drootofallevil@...> wrote:
Thanks for responding Jim You could have a transformer with such bad steel that the magnetizing current dominates the reflected current from the load, but nobody wants one of those. I don¡¯t know if somehow we are talking past each other somehow bu Mr Faraday was working with induction coils ¡°When was the transformer invented? A: The property of induction was discovered in the 1830's but it wasn't until 1886 that , working for Westinghouse built the first reliable commercial transformer.¡± ? Anyhow, Halden¡¯s current was about in-phase with the voltage [ I copied and shifted the current which is not perfectly symmetrical, but was not able come up with any shift ], so the load current was determining the ?primary current ?no matter how meaningless you think it is. ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Monday, August 5, 2024 5:25 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? Don The load on the transformer is meaningless since the primary is fed with 31 volts instead of 120 volts RMS.? Since power is proportional to voltage squared, no real work is being done, nothing is getting warm.? The transformer is not stressed as it would be powering the transmitter.?? ? Lots of interesting things happen as the power transformer nears saturation.? So yes, a trivial load should be "glossed over" as you say. ? I support the interest shown in finding the cause of the power transformer failure.? I am all for experimenting and testing.? Some faulty assumptions have been made which now contradict the fundamental findings of Faraday and Henry which were made some 200 years ago.? I'm just try to improve the experimental techniques and get it back on track. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy ? ? On Monday, August 5, 2024 at 01:45:19 PM CDT, don Root <drootofallevil@...> wrote: ? ? Hi Jim , I believe your description,? but? you seem to have glossed over the fact that Halden¡¯s? tests? had a load on the transformer secondary, and that can¡¯t be ignored. if you remove the load, then your portrayal is likely reasonable ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io ? Don There is no difference between two inductors and a transformer if the two inductors are coupled together only by a common magnetic field.? The tighter the coupling between the two inductors, the more power that is transferred from one inductor to the other.? In other words, they transform power from one to the other. ? If you are skeptical and you have a working radio or power amplifier with a 70 volt audio output, you can collocate? two 70 volt line transformers on the bench.? Connect one to the 70 volt audio using the 10 or so watt tap and terminate it's output in an 8 ohm power resistor.? Connect the other line transformer output to an 8 ohm speaker.? Set the volume control for a decent volume.? The closer the two line transformers are to each other, the more audio that is coupled from one line transformer to the other and then to the speaker.? Perhaps the highest volume is when one is stacked on the other.? I have done this experiment. ? This may help explain why some radios always have a slight hum in the speaker if the power transformer and the audio output transformer are collocated on the chassis. Regards, Jim
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Jim Whartenby
Peter A Markavage
don Root
waltcates