Flux density in the core is actually highest at no load. As you add load, it decreases. Most power transformers (mains frequency types) are slightly saturating at no load. This is done to keep the core size down and, perhaps, to keep the number of turns down (length of copper wire) for better load regulation.
That grounded connection shown on the diagram is typically an electrostatic shield, a sheet of copper in between the windings, and NOT a ground for the core laminations. It's my understanding that the individual lamination are coated with varnish and ideally, for the sake of efficient energy transfer between primary and secondary, should not be electrically connected to each other (and the bolts holding the laminations together are often insulated with a cardboard or plastic tube). That said, in a cheaply made transformer, or an older transformer, or one that has been exposed to moisture and has grown rust crystals inbetween or around the edges of the lamnations, there are probably numerous connections between the laminate plates, causing flux leakage and inefficiency, perhaps even causing overheating.
Tony, thank you very much for taking your valuable time to make these videos, much appreciated! There sure is more to electricity/electronics than the average person realizes, but it sure is fun and interesting. 🙂
You can use a transformer for DC, you just have to turn the DC on and off in pulses. This is how switch mode power supplies work. The advantage of high frequency DC switching over the 60Hz AC, is that transformers can be built much smaller due to less magnetic flux.
At some point in the past, military aircraft used 400Hz alternators and 400 Hz transformers, presumably for purposes of efficiency and lower weight. Similarly it is worth noting that modern transformers need to have a larger core if they are going to be efficient at 50 Hz mains frequency rather than the 60 Hz that is standard in the US.
Wow. What a great series. It has been about 20 years since I fiddled with any vacuum tube amp circuits. I forgot a lot of stuff. My previous question here (now removed) about the voltages inside this amp was answered ... all the way at the end of the series in the last 2 or 3 videos where a lot of testing and adjustment was done. MUST WATCH all the way through everyone!
@21.40 It might be worth noting that when connecting the two primaries in series or parallel it's vitally important to observe the correct phase of the windings. If the phases are correct it works. If the phases are wrong the magnetic flux is exactly canelled out and bye bye transformer or at least the fuse.
Thank you for bringing that up! I forgot to mention that. You are absolutely correct. They make no mention of this in the schematic for this JABOP amp, but the primary wires are color coded red and black (who knows why they used those colors). For 110VAC use, you wire red to red and black to black. For 220 VAC, you wire the black from one winding to the red of the other winding. Thanks again!
Excellent explanation of the power transformer, I've ben in a fog for a while about them but you've cleared it all away..Thanks for sharing your expert knowledge..Ed..uk..😀
Another thing worth mentioning is that the highest quality power transformers are, or at least sometimes may carry the designation CCS which stands for *continuous commercial service*. Most transformers used in consumer-grade equipment, howevers, were designed for intermittent service and so it's assumed that they might run for a couple hours or the better part of a day but will have a shutdown period for cooling off.
Interesting. Now CCS mostly stands for "copper coated steel", which is definitely the last thing to look for in a transformer :D (It also stands for constant current source / sink, but it doesn't relate as much)
I feel like I am back in my first year of college (1970's). I understood core is laminated is so each layer is ELECTRICALLY insulated between each. This stops the electrical eddy-currents from moving between layers. Magnetic eddy-currents are largely unaffected.
This is my understanding as well, that the individual lamination sheets were varnished to prevent them from electrically contacting each other; I have seen transformers with cardboard or plastic sleeves over the bolts binding the laminations together together in order to prevent short-circuiting them electrically. How strict the manufacturers were about maintaining this physical/ electrical separation between lamanations likely varied significantly from one manufacturer to another, and the magnetic and capacitive isolation probably varied in inverse proportion to the price point that the transformer was made to! Formation of rust crystals inbetween and around the edges of the laminations, as often seen in vintage amplifiers, is supposedly a bad thing in terms of transformer efficiency.
Actually, this type of transformer is simply dipped in varnish as a completed unit. The term "laminated" refers to the fact that the core is comprised of individual pieces of "laminations" stacked together. The major purpose of the varnish is to soak into the paper insulation (and lead anchor tape) between layers/windings of the coil for structural purposes and to minimize moisture effects within the coil. (Most bobbin-wound xfmrs. are not varnished). In the varnish dip process, there is very little penetration into the core (between individual laminations). Most power transformers for applications such as radios and amplifiers (produced in volume) are specified for the application to ensure meeting its unique requirements while minimizing cost.
@@whollyunaware5185 , I am aware that dipping a transformer in varnish after the fact is done not to isolate the laminations but to fix the coils in place and prevent buzzing and so on (ideally done under vacuum so as to displace air and allow full penetration of the vaarnish). However, if you take transformers apart, some units will appear to have individually painted or anodized or otherwise coated laminations. Ss Tony mentioned, the basic theory says that maximum electromagnetic efficiency is achieved if each lamination is isolated from its brothers and sisters. Most transformer manufacturers likely don't bother to do this.
@@goodun2974 The coating you may have seen on individual laminations may be the oil that is applied by the lamination manufacturer to facilitate the use of lamination stacking machines. Besides the cost-prohibitive concerns of impregnating (and baking) individual laminations, lumps and air bubbles would render machine laminating impracticable. The purpose of varnish impregnation (dip or more-expensive vacuum) is to seal the coil for environmental concerns (generally not applicable to commercial radios, etc.). The bi-product of avoiding rust on surfaces of the lamination stack and mounting hardware is more an aesthetic value.
I would consider using the tubes designed in 1957 for use in Car Radios without vibrator converters and using two VN66AF VMOS FETs for the Push Pull output stage and just using a H+ of 12V for the heater and the B+ of 12V which would make for a nice safe unit and could be run of a car battery.
@@KeritechElectronics , I have indeed found this to be true. My wife tends to be "cold all the time" and sometimes uses me as a giant mobile handwarmer; she is especially happy to have me warm her up after the sun has set, and seems to have a positive temperature coefficient ---- the warmer she gets, the less resistant she becomes!
I have to wonder if that Fisher mono-block amplifier you mentioned with the hot running transformer ran equally hot back when it was made and the AC mains wall-voltages were lower, not to mention that the characteristics of the transformer itself may have changed over the years. Laminations that were originally insulated from each other may have become conductive due to rust or moisture infiltration.
Another reason we use AC mains: To transfer DC Current over long distances.... VERY large conductors must be used and is lossy. AC current at high voltages can travel 100s of miles through thinner conductors with comparatively little loss.
Not really, 750kV HVDC lines exist and are doing great, it's about the relative ease with which one can convert AC voltages. Losses are proportional to current squared, regardless whether we're running AC or DC through the conductors and in fact lower in DC lines thanks to no repeated charging/discharging of line capacitances/power factor related losses. In fact, for a given voltage the power delivered will be greater for a DC line, as Tony explains. End of the line equipment is still more costly than in case of AC, however lines itself are quite the opposite and especially so for under the sea transmission. Remember also, that you no longer need multiple conductors to facilitate 3 phase infrastructure. China leads the way with multiple HVDC lines, some exceeding 1 million volts with Made in Germany ABB, Alstom and Siemens equipment.
As Paul B says, it's not the transfer, but the Voltage Conversion that is problematic for DC. Even a humble SwitchMode Power Supply needs to convert the DC to AC, change the voltage, then convert it back to DC again. That gets incredibly complex when you are trying to supply GigaWatts.
@@johncoops6897 I understand now... AC makes it trivial to step-up to high voltages for cross-country transfer (lower current, small conductors)...then step back down on other end. The end result is less power-loss with lower-cost conductors.
How does one choose the right transformer for an audio amp? There are so many variables and transformer types to choose from, and even more amp designs available for free on the wibbly wobbly web.
The video explains what you are asking. You choose the transformer SIZE based on whatever power you need. There aren't really any variables... you need a certain amount of power at certain voltages, so you choose the transformer size to match. The KIND of transformer is based on price. The more that you pay, the better the transformer. Simple "E-I" core transformers like shown in this video are the cheapest. There are Toroidal transformers that cost a LOT more and produce less noise (hum). There are even more expensive transformers that are better for noise. But really, a conventional transformer is usually good enough. As I said, everything that you are asking is explained in this video... so just watch it.
If you're making a joke or referencing something, it went over my head. If you're genuinely asking, it isn't Eddie current, it's eddy current, and the term comes from fluid dynamics.
Hi, Tony I have a couple of transformers that came out of some President/Uniden base station cb radio, there isn't any information on the transformer, how can you tell whether the only 2 wires on primary are 120v or 240v, ?can you test with DMM impedance? Much appreciated PeaceFromOZ
Thankyou for your clear carefull explanations,although I did have my hope for free energy excited at 10:00 the diagram suggests two 110v primary's obtained from one 110v mains supply?
If I wired that transformer in a circuit using conventional wiring color codes many bad things will happen including an unplanned light show. My standards the way I was taught is Black- Black is primary, Red--red/yellow-Red is HV secondary; Green-Green is filament voltage; and Yellow-Yellow is the 5 volt for the rectifier tube filament. It must be a transformer that came from somewhere else.
"It must be a transformer that came from somewhere else". If you watch the video all will become clear. If you "wired that transformer in a circuit using conventional wiring color codes" you would not be paying attention to the situation. Many vintage transformers have no discernible wire colours and must be worked out from basic principles. A competent thoughtful person would have no trouble in deciding how to connect such a device, indeed such an exersise is an enjoyable part of involvement with the project.
I have a microwave transformer re-winded for 24 ac but even at standby it gets so hot in just a few minutes! The core is isolated from both windings, but when i check ac i get some volts around core Is it normal? Why it's getting to hot?
MOTs were not designed to be used in that way. They are a variable reluctance transformer with an air gap and shunt, used to regulate/limit the current. If you change the windings, shunt or air gap width, it could greatly affect the properties of the transformer. If driven into saturation, they will draw very heavy current and the core will heat up abnormally. I would avoid messing with MOTs, unless you know how they work, as they can be more bother than they're worth, for modifying. ;)
@@xraytonyb yes you're right I removed shunt and i think it's one of main reasons. Also i can get some ac voltage! When I check the core with multimeter! I think it just worth for spot welding and nothing else
So? DC was unfeasible for long distance transmission back then because you needed to transform it to AC, transform it up and then convert back to get any appreciateable transmission distance. As low voltage DC needs thick expensive conductors and can't get that far. You need high voltage for long distance which wasn't possible in purely DC back then. Otherwise you would have needed a power station per city district. Also back then most home appliances only needed AC as they mostly used heating elements, AC motors or light bulbs. Low voltage DC applications didn't really exist up until the 20ies in the typical home.
I'm sorry to have to be "that guy", but I can only listen to you say "less turns" so many times before my brain is on the verge of exploding! Please use "fewer turns" instead.
Flux density in the core is actually highest at no load. As you add load, it decreases. Most power transformers (mains frequency types) are slightly saturating at no load. This is done to keep the core size down and, perhaps, to keep the number of turns down (length of copper wire) for better load regulation.
That grounded connection shown on the diagram is typically an electrostatic shield, a sheet of copper in between the windings, and NOT a ground for the core laminations. It's my understanding that the individual lamination are coated with varnish and ideally, for the sake of efficient energy transfer between primary and secondary, should not be electrically connected to each other (and the bolts holding the laminations together are often insulated with a cardboard or plastic tube). That said, in a cheaply made transformer, or an older transformer, or one that has been exposed to moisture and has grown rust crystals inbetween or around the edges of the lamnations, there are probably numerous connections between the laminate plates, causing flux leakage and inefficiency, perhaps even causing overheating.
One of the best explanations of what and how a transformer is and works.
Tony, thank you very much for taking your valuable time to make these videos, much appreciated! There sure is more to electricity/electronics than the average person realizes, but it sure is fun and interesting. 🙂
Great series. You're a great teacher. Keep them lessons comming.. :)
I love the hand motions. It's like watching a silent Lon Chaney film.
You can use a transformer for DC, you just have to turn the DC on and off in pulses. This is how switch mode power supplies work. The advantage of high frequency DC switching over the 60Hz AC, is that transformers can be built much smaller due to less magnetic flux.
At some point in the past, military aircraft used 400Hz alternators and 400 Hz transformers, presumably for purposes of efficiency and lower weight. Similarly it is worth noting that modern transformers need to have a larger core if they are going to be efficient at 50 Hz mains frequency rather than the 60 Hz that is standard in the US.
@@goodun2974 yes, transformer size is inversely proportional to frequency
Thank you for making this series. I appreciate it very much!
Wow. What a great series. It has been about 20 years since I fiddled with any vacuum tube amp circuits. I forgot a lot of stuff.
My previous question here (now removed) about the voltages inside this amp was answered ... all the way at the end of the series in the last 2 or 3 videos where a lot of testing and adjustment was done. MUST WATCH all the way through everyone!
@21.40 It might be worth noting that when connecting the two primaries in series or parallel it's vitally important to observe the correct phase of the windings. If the phases are correct it works. If the phases are wrong the magnetic flux is exactly canelled out and bye bye transformer or at least the fuse.
Thank you for bringing that up! I forgot to mention that. You are absolutely correct. They make no mention of this in the schematic for this JABOP amp, but the primary wires are color coded red and black (who knows why they used those colors). For 110VAC use, you wire red to red and black to black. For 220 VAC, you wire the black from one winding to the red of the other winding. Thanks again!
@@xraytonyb Might be worth mentioning this in a later video in case anyone is about to connect them wrongly.
This is a first, to see green as high voltage and yellow as filament. It's usually green for filament, and yellow as 5V. SO much for Standards!
Excellent explanation of the power transformer, I've ben in a fog for a while about them but you've cleared it all away..Thanks for sharing your expert knowledge..Ed..uk..😀
Thank you for your time and precise explanation about transformer.
Great transformer lesson! Learning a lot.
20:24 - Interesting color-coding on the wires. Red-black usually implies DC! Green-green and green/yellow usually signify the low-voltage secondary!
Another thing worth mentioning is that the highest quality power transformers are, or at least sometimes may carry the designation CCS which stands for *continuous commercial service*. Most transformers used in consumer-grade equipment, howevers, were designed for intermittent service and so it's assumed that they might run for a couple hours or the better part of a day but will have a shutdown period for cooling off.
Interesting. Now CCS mostly stands for "copper coated steel", which is definitely the last thing to look for in a transformer :D
(It also stands for constant current source / sink, but it doesn't relate as much)
@@KeritechElectronics , there was also a designation for consumer-grade transformers, ICAS I think, for Intermittent something something Service....
Best thing about transformers is that they isolate the voltage from the mains.
Yes, unless it is an “auto transformer” like a Variac, then be very careful as you are not isolated from the mains!
Nice work, thanks.
I feel like I am back in my first year of college (1970's). I understood core is laminated is so each layer is ELECTRICALLY insulated between each. This stops the electrical eddy-currents from moving between layers. Magnetic eddy-currents are largely unaffected.
This is my understanding as well, that the individual lamination sheets were varnished to prevent them from electrically contacting each other; I have seen transformers with cardboard or plastic sleeves over the bolts binding the laminations together together in order to prevent short-circuiting them electrically. How strict the manufacturers were about maintaining this physical/ electrical separation between lamanations likely varied significantly from one manufacturer to another, and the magnetic and capacitive isolation probably varied in inverse proportion to the price point that the transformer was made to! Formation of rust crystals inbetween and around the edges of the laminations, as often seen in vintage amplifiers, is supposedly a bad thing in terms of transformer efficiency.
Actually, this type of transformer is simply dipped in varnish as a completed unit. The term "laminated" refers to the fact that the core is comprised of individual pieces of "laminations" stacked together. The major purpose of the varnish is to soak into the paper insulation (and lead anchor tape) between layers/windings of the coil for structural purposes and to minimize moisture effects within the coil. (Most bobbin-wound xfmrs. are not varnished). In the varnish dip process, there is very little penetration into the core (between individual laminations). Most power transformers for applications such as radios and amplifiers (produced in volume) are specified for the application to ensure meeting its unique requirements while minimizing cost.
@@whollyunaware5185 , I am aware that dipping a transformer in varnish after the fact is done not to isolate the laminations but to fix the coils in place and prevent buzzing and so on (ideally done under vacuum so as to displace air and allow full penetration of the vaarnish). However, if you take transformers apart, some units will appear to have individually painted or anodized or otherwise coated laminations. Ss Tony mentioned, the basic theory says that maximum electromagnetic efficiency is achieved if each lamination is isolated from its brothers and sisters. Most transformer manufacturers likely don't bother to do this.
@@goodun2974 The coating you may have seen on individual laminations may be the oil that is applied by the lamination manufacturer to facilitate the use of lamination stacking machines. Besides the cost-prohibitive concerns of impregnating (and baking) individual laminations, lumps and air bubbles would render machine laminating impracticable. The purpose of varnish impregnation (dip or more-expensive vacuum) is to seal the coil for environmental concerns (generally not applicable to commercial radios, etc.). The bi-product of avoiding rust on surfaces of the lamination stack and mounting hardware is more an aesthetic value.
I would consider using the tubes designed in 1957 for use in Car Radios without vibrator converters and using two VN66AF VMOS FETs for the Push Pull output stage and just using a H+ of 12V for the heater and the B+ of 12V which would make for a nice safe unit and could be run of a car battery.
This lecture dove-tails nice with my current power-amp project that is using two toroidal power transformers. (two amps in one chassis)
Thank you for making the time to produce such awesome videos!
Keep up the great work!! :)
Excellent. Thank you soooo much!
Hi Tony, Absolutely Brilliant ! Thank you so much , keep them coming.
Reluctance and permeability-sounds like two terms wives invented 😉😂
Cringe-worthy jokes have been formulated around the term *perveance*.
@@goodun2974 let's not forget the second Ohm's law!
@@KeritechElectronics , second ohms law?okay, I'll bite.....🤔😳
@@goodun2974 it goes lilke "body's resistance decreases in darkness"
@@KeritechElectronics , I have indeed found this to be true. My wife tends to be "cold all the time" and sometimes uses me as a giant mobile handwarmer; she is especially happy to have me warm her up after the sun has set, and seems to have a positive temperature coefficient ---- the warmer she gets, the less resistant she becomes!
Best explanation I’ve seen so far about transformers
Will take at least 2 more times watching to get it- thanks for the video
Great stuff, thanks.
Uncle Doug does a lot of videos on tube biasing and plate dissipation currents
Amazing content
Nice
looks like a nice well insulated cores and safe transformer:-)
While you were describing 'losses' in xFormers, I almost expected to hear the word 'entropy' and the 2nd law of thermodynamics. 8-)
Why are transformers days gone by much larger and heavier
I have to wonder if that Fisher mono-block amplifier you mentioned with the hot running transformer ran equally hot back when it was made and the AC mains wall-voltages were lower, not to mention that the characteristics of the transformer itself may have changed over the years. Laminations that were originally insulated from each other may have become conductive due to rust or moisture infiltration.
Thank you.
Another reason we use AC mains: To transfer DC Current over long distances.... VERY large conductors must be used and is lossy. AC current at high voltages can travel 100s of miles through thinner conductors with comparatively little loss.
Not really, 750kV HVDC lines exist and are doing great, it's about the relative ease with which one can convert AC voltages. Losses are proportional to current squared, regardless whether we're running AC or DC through the conductors and in fact lower in DC lines thanks to no repeated charging/discharging of line capacitances/power factor related losses. In fact, for a given voltage the power delivered will be greater for a DC line, as Tony explains. End of the line equipment is still more costly than in case of AC, however lines itself are quite the opposite and especially so for under the sea transmission. Remember also, that you no longer need multiple conductors to facilitate 3 phase infrastructure. China leads the way with multiple HVDC lines, some exceeding 1 million volts with Made in Germany ABB, Alstom and Siemens equipment.
As Paul B says, it's not the transfer, but the Voltage Conversion that is problematic for DC.
Even a humble SwitchMode Power Supply needs to convert the DC to AC, change the voltage, then convert it back to DC again. That gets incredibly complex when you are trying to supply GigaWatts.
@@johncoops6897 I understand now... AC makes it trivial to step-up to high voltages for cross-country transfer (lower current, small conductors)...then step back down on other end. The end result is less power-loss with lower-cost conductors.
I sure does dude good guy
Is a discussion of potentiometer types and their evolution in store for a future episode?
How does one choose the right transformer for an audio amp? There are so many variables and transformer types to choose from, and even more amp designs available for free on the wibbly wobbly web.
The video explains what you are asking. You choose the transformer SIZE based on whatever power you need. There aren't really any variables... you need a certain amount of power at certain voltages, so you choose the transformer size to match.
The KIND of transformer is based on price. The more that you pay, the better the transformer. Simple "E-I" core transformers like shown in this video are the cheapest. There are Toroidal transformers that cost a LOT more and produce less noise (hum). There are even more expensive transformers that are better for noise. But really, a conventional transformer is usually good enough.
As I said, everything that you are asking is explained in this video... so just watch it.
Now I know why I respected EE majors
Yes, I get that about the magnetic flux, but who is Eddie?
If you're making a joke or referencing something, it went over my head. If you're genuinely asking, it isn't Eddie current, it's eddy current, and the term comes from fluid dynamics.
@@stevencraig yes, it's a joke.
Lol
Xraytonyb the power transformer is cool
i'd like to add an isolation transformer to my magnavox 3 tube stereo amplifier, but wonder how i can re-wire the filaments in paralell
Just use a 1:1 mains voltage transformer and ground the chassis.
Hi, Tony I have a couple of transformers that came out of some President/Uniden base station cb radio, there isn't any information on the transformer, how can you tell whether the only 2 wires on primary are 120v or 240v, ?can you test with DMM impedance?
Much appreciated
PeaceFromOZ
Thankyou for your clear carefull explanations,although I did have my hope for free energy excited at 10:00 the diagram suggests two 110v primary's obtained from one 110v mains supply?
Is that part of the green new steal?
@@janicehopkins4432 lol, i'am sure they would find a way to make us pay for 'free energy', but wouldnt it stop thier need for a climate scam also?
If I wired that transformer in a circuit using conventional wiring color codes many bad things will happen including an unplanned light show. My standards the way I was taught is Black- Black is primary, Red--red/yellow-Red is HV secondary; Green-Green is filament voltage; and Yellow-Yellow is the 5 volt for the rectifier tube filament. It must be a transformer that came from somewhere else.
Chinese made, Chinese color code. They don't stick to non-commie American standards.
Chinese for sure, good thing there is a map on the side of it!
There are no "standards" for wiring colors. That is why there is a schematic.
"It must be a transformer that came from somewhere else". If you watch the video all will become clear. If you "wired that transformer in a circuit using conventional wiring color codes" you would not be paying attention to the situation. Many vintage transformers have no discernible wire colours and must be worked out from basic principles. A competent thoughtful person would have no trouble in deciding how to connect such a device, indeed such an exersise is an enjoyable part of involvement with the project.
I have a microwave transformer re-winded for 24 ac but even at standby it gets so hot in just a few minutes! The core is isolated from both windings, but when i check ac i get some volts around core
Is it normal?
Why it's getting to hot?
MOTs were not designed to be used in that way. They are a variable reluctance transformer with an air gap and shunt, used to regulate/limit the current. If you change the windings, shunt or air gap width, it could greatly affect the properties of the transformer. If driven into saturation, they will draw very heavy current and the core will heat up abnormally. I would avoid messing with MOTs, unless you know how they work, as they can be more bother than they're worth, for modifying. ;)
@@xraytonyb yes you're right
I removed shunt and i think it's one of main reasons. Also i can get some ac voltage! When I check the core with multimeter!
I think it just worth for spot welding and nothing else
I will let you go now.
awsum
Did you hear the war on AC vs DC criminal........and yet today most product use DC so?????
So?
DC was unfeasible for long distance transmission back then because you needed to transform it to AC, transform it up and then convert back to get any appreciateable transmission distance. As low voltage DC needs thick expensive conductors and can't get that far. You need high voltage for long distance which wasn't possible in purely DC back then. Otherwise you would have needed a power station per city district.
Also back then most home appliances only needed AC as they mostly used heating elements, AC motors or light bulbs. Low voltage DC applications didn't really exist up until the 20ies in the typical home.
There aren't any AC Batteries... so we prefer DC for our gadgets.
I'm sorry to have to be "that guy", but I can only listen to you say "less turns" so many times before my brain is on the verge of exploding! Please use "fewer turns" instead.