Hello averybody,
I'm trying to figuring me up how does the electromagnetic dynamic speaker work. I have 6 wires and I can't identify their function. Particulary I want to know what is the field coil.
Thanks in advance.
Carlos from Chile

That's easy- the field coil will be the one with the highest resistance.

The voice coil will be the one with lowest resistance.

The hum bucker will be the one that's left.

- Nat

:Hello averybody,
:I'm trying to figuring me up how does the electromagnetic dynamic speaker work. I have 6 wires and I can't identify their function. Particulary I want to know what is the field coil.
:Thanks in advance.
:Carlos from Chile

Though those items mentioned would produce the correct combination of 6 wires, I only hope that the speaker doesn't have an output transformer. The two wires that go into what would be the magnet section of a modern speaker would be the field coil wires if the impedance across these wires is high, from perhaps 200 to sever thousand ohms, though if it is an automobile speaker, the resistance will be only one to several ohms because the speaker is driven off the 6 volt supply. Two more wires that come out of one extreme end of the "magnet section," which have a very low impedance across them (in the neighborhood of 1 ohm), would be the hum bucking coil wires. To eliminate hum, this coil is hooked in series with the voice coil. Reverse the direction it is hooked up to see if this eliminates hum better. Only one way will work.

Now, your speaker may have two leads or terminals coming out of the conventional place that modern speakers have voice coil terminals. It might also have a transformer looking device, which in fact is a transformer, which is wired to these terminals, and then wires protrude from the other side of the transformer. These wires on the other side will actually have a rather high impedance from several hundred to several thousand ohms. If there is no output transformer on the speaker, of course the voice coil will have a very low impedance in the neighborhood of 1 ohm, perhaps more, perhaps less. If the speaker has an output transformer with three wires coming out one side (and two to the voice coil on the other), then this transformer is designed for push-pull operation, with each end lead going to one output tube plate, and the center lead going to B+ at a designated point.

I worry about what the previous person said, because I have yet to see a speaker where both leads of the hum bucking coil leave the speaker. One is always tied to one side of the voice coil, and the remaining hum bucking coil and voice coil leads (two total) are sent to the transformer, whether it be on the radio or on the speaker itself. The remaining two wires would then be the field coil wires. This combination, whether the transformer was on the speaker or radio, would only yield 4 wires, unless the transformer, mounted to the speaker, was a push-pull type, which would yield a total of 5 wires.

Still, someone could have cut all of the wires on the speaker so that they are not wired to eachother. In this case, you would actually have 6 separate wires, considering that either the output transformer was of the two wire, single tube variety, or that the output transformer was not mounted to this particular speaker. In this case, you would have the two hum bucking wires, the two field wires, and the two voice coil wires, either coming directly from the speaker, or if a transformer is present, you would have the two high impedance leads coming from the primary of the transformer. The hum bucking coil, if a transformer is mounted to the speaker, should be wired in series with one secondary transformer lead and one voice coil lead. The other secondary lead should be connected to the other voice coil lead.

Sorry for being too complicated, but this really can be a complicated matter, not a simple one.

Thomas

Thanks Thomas,
you are right, it shoul be a transformer but it isn't. Actually 6 wires are from the speaker as you suspect, so I have to find that transformer. I would like try connect an modern speaker and replace the speaker fied by a resistor, saying 470 ohm, 10 W. What do you think?
Regards
Carlos

:Though those items mentioned would produce the correct combination of 6 wires, I only hope that the speaker doesn't have an output transformer. The two wires that go into what would be the magnet section of a modern speaker would be the field coil wires if the impedance across these wires is high, from perhaps 200 to sever thousand ohms, though if it is an automobile speaker, the resistance will be only one to several ohms because the speaker is driven off the 6 volt supply. Two more wires that come out of one extreme end of the "magnet section," which have a very low impedance across them (in the neighborhood of 1 ohm), would be the hum bucking coil wires. To eliminate hum, this coil is hooked in series with the voice coil. Reverse the direction it is hooked up to see if this eliminates hum better. Only one way will work.
:
:Now, your speaker may have two leads or terminals coming out of the conventional place that modern speakers have voice coil terminals. It might also have a transformer looking device, which in fact is a transformer, which is wired to these terminals, and then wires protrude from the other side of the transformer. These wires on the other side will actually have a rather high impedance from several hundred to several thousand ohms. If there is no output transformer on the speaker, of course the voice coil will have a very low impedance in the neighborhood of 1 ohm, perhaps more, perhaps less. If the speaker has an output transformer with three wires coming out one side (and two to the voice coil on the other), then this transformer is designed for push-pull operation, with each end lead going to one output tube plate, and the center lead going to B+ at a designated point.
:
:I worry about what the previous person said, because I have yet to see a speaker where both leads of the hum bucking coil leave the speaker. One is always tied to one side of the voice coil, and the remaining hum bucking coil and voice coil leads (two total) are sent to the transformer, whether it be on the radio or on the speaker itself. The remaining two wires would then be the field coil wires. This combination, whether the transformer was on the speaker or radio, would only yield 4 wires, unless the transformer, mounted to the speaker, was a push-pull type, which would yield a total of 5 wires.
:
:Still, someone could have cut all of the wires on the speaker so that they are not wired to eachother. In this case, you would actually have 6 separate wires, considering that either the output transformer was of the two wire, single tube variety, or that the output transformer was not mounted to this particular speaker. In this case, you would have the two hum bucking wires, the two field wires, and the two voice coil wires, either coming directly from the speaker, or if a transformer is present, you would have the two high impedance leads coming from the primary of the transformer. The hum bucking coil, if a transformer is mounted to the speaker, should be wired in series with one secondary transformer lead and one voice coil lead. The other secondary lead should be connected to the other voice coil lead.
:
:Sorry for being too complicated, but this really can be a complicated matter, not a simple one.
:
:Thomas

You should use a choke if possible. The field coil was part of the B+ filtering system in most radios and simply replacing it with a resistor may result in increased hum. If you do use a resistor you may have to increase the size of the filter capacitors to compensate.

:Thanks Thomas,
:you are right, it shoul be a transformer but it isn't. Actually 6 wires are from the speaker as you suspect, so I have to find that transformer. I would like try connect an modern speaker and replace the speaker fied by a resistor, saying 470 ohm, 10 W. What do you think?
:Regards
:Carlos
:

If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.

Thomas

Hi Thomas,
The output tube is the 25L6G.
Thanks

:If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.
:
:Thomas

What's the model of the radio?....name, number, etc.

Thomas

:Hi Thomas,
:The output tube is the 25L6G.
:Thanks
:
::If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.
::
::Thomas

It's a Dewald 637, early 1938. File M0004268.pdf

:What's the model of the radio?....name, number, etc.
:
:Thomas
:
::Hi Thomas,
::The output tube is the 25L6G.
::Thanks
::
:::If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.
:::
:::Thomas

The transformers I would recommend would be numbers
P-T125ASE
and
P-T125BSE

The former is a 3 watt version, and the latter is a 5 watt version. The three watt version is all you really need, but the 5 watt may give you cleaner sound. I doubt you will notice a difference, though.

Go to www.tubesandmore.com and select TRANSFORMERS in the left hand list. Select SINGLE ENDED from the transformers list. The first two transformers listed in the single ended list will be the ones I mentioned. Something to keep in mind when reading the impedance values listed is that these impedances are usually taken with a frequency of about 1,000 cycles. Taking a measurement of the voice coil on your speaker with your multi-meter (which uses direct current) will yield a much lower impedance. For instance, a 4 ohm voice coil will probably only read about 1 ohm on your meter. Perhaps 2. This is why you must do the following when wiring the transformer to your speaker and radio:

When you get the transformer, hook the primary up to the plate of the 25L6 and B+. Starting with the largest resistance, work your way down until the audio is the way you like it--should be clean and undistorted, and also so that the bass response is strong enough. The lowest resistance may yield the loudest sound, but may not yield the best bass response or the proper plate voltage. Make sure that the voltage at the plate of the 25L6 is approximately where it should be. Remember that this voltage is approximate, and can be slightly higher. Aim for the loudest, most pleasing, undistorted sound, one that is not too sharp or too muffled.

Then select the appropriate secondary that also gives the loudest and most pleasing undistorted sound. Wire one lead of the secondary to the voice coil of your speaker. Wire the other voice coil lead to the hum bucking coil. Wire the other hum bucking coil lead to the remaining secondary lead. Listen to the hum in the speaker with the radio at minimum volume. Reverse the hum bucking coil connections and note which ones produce the least amount of hum. Connect the hum bucking coil the way that reduces hum the most.

Of course, to do all of the above adjustments, you must initially wire up the speaker as stated above, but choose the highest resistance taps for the primary and secondary. Then work your way down to where you like it.

Cut off the remaining primary leads and dress them so that they may not be exposed. Do not connect any of the primary or secondary leads together as this will short out the transformer. If the speaker does not have a place for a transformer, or even if it does, if you wish you may mount the transformer under the chassis where it won't be seen. This way the modern transformer won't take away from the appearance of the set. You will then have four wires going to the speaker--two for the voice coil and two for the field coil. You can also mount the transformer on the speaker and dress the wires with cloth spaghetti, which is sold by www.tubesandmore.com

Be sure that the field and voice coils of your speaker are in good order. If they are open, the speaker won't work. If the speaker is broken, and you don't feel that you can repair it, you may purchase a modern speaker of the same size, and since you are purchasing a universal output transformer, you may adapt the transformer to this speaker, even if it has a different voice coil impedance. The secondary of the transformer has terminals mounted right to the transformer, so changes may be made for any speaker. If a modern speaker is used, a 10 to 15 watt resistor of similar impedance must be substituted for the field coil.

Thomas

:It's a Dewald 637, early 1938. File M0004268.pdf
:
::What's the model of the radio?....name, number, etc.
::
::Thomas
::
:::Hi Thomas,
:::The output tube is the 25L6G.
:::Thanks
:::
::::If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.
::::
::::Thomas

Thank you Thomas, tomorrow I'll go for a new transformer. I'll try to find it here in Chile first.

Thanks again.
(about grammar subject, I was joking too. No worries :)

:The transformers I would recommend would be numbers
:P-T125ASE
:and
:P-T125BSE
:
:The former is a 3 watt version, and the latter is a 5 watt version. The three watt version is all you really need, but the 5 watt may give you cleaner sound. I doubt you will notice a difference, though.
:
:Go to www.tubesandmore.com and select TRANSFORMERS in the left hand list. Select SINGLE ENDED from the transformers list. The first two transformers listed in the single ended list will be the ones I mentioned. Something to keep in mind when reading the impedance values listed is that these impedances are usually taken with a frequency of about 1,000 cycles. Taking a measurement of the voice coil on your speaker with your multi-meter (which uses direct current) will yield a much lower impedance. For instance, a 4 ohm voice coil will probably only read about 1 ohm on your meter. Perhaps 2. This is why you must do the following when wiring the transformer to your speaker and radio:
:
:When you get the transformer, hook the primary up to the plate of the 25L6 and B+. Starting with the largest resistance, work your way down until the audio is the way you like it--should be clean and undistorted, and also so that the bass response is strong enough. The lowest resistance may yield the loudest sound, but may not yield the best bass response or the proper plate voltage. Make sure that the voltage at the plate of the 25L6 is approximately where it should be. Remember that this voltage is approximate, and can be slightly higher. Aim for the loudest, most pleasing, undistorted sound, one that is not too sharp or too muffled.
:
:Then select the appropriate secondary that also gives the loudest and most pleasing undistorted sound. Wire one lead of the secondary to the voice coil of your speaker. Wire the other voice coil lead to the hum bucking coil. Wire the other hum bucking coil lead to the remaining secondary lead. Listen to the hum in the speaker with the radio at minimum volume. Reverse the hum bucking coil connections and note which ones produce the least amount of hum. Connect the hum bucking coil the way that reduces hum the most.
:
:Of course, to do all of the above adjustments, you must initially wire up the speaker as stated above, but choose the highest resistance taps for the primary and secondary. Then work your way down to where you like it.
:
:Cut off the remaining primary leads and dress them so that they may not be exposed. Do not connect any of the primary or secondary leads together as this will short out the transformer. If the speaker does not have a place for a transformer, or even if it does, if you wish you may mount the transformer under the chassis where it won't be seen. This way the modern transformer won't take away from the appearance of the set. You will then have four wires going to the speaker--two for the voice coil and two for the field coil. You can also mount the transformer on the speaker and dress the wires with cloth spaghetti, which is sold by www.tubesandmore.com
:
:Be sure that the field and voice coils of your speaker are in good order. If they are open, the speaker won't work. If the speaker is broken, and you don't feel that you can repair it, you may purchase a modern speaker of the same size, and since you are purchasing a universal output transformer, you may adapt the transformer to this speaker, even if it has a different voice coil impedance. The secondary of the transformer has terminals mounted right to the transformer, so changes may be made for any speaker. If a modern speaker is used, a 10 to 15 watt resistor of similar impedance must be substituted for the field coil.
:
:Thomas
:
::It's a Dewald 637, early 1938. File M0004268.pdf
::
:::What's the model of the radio?....name, number, etc.
:::
:::Thomas
:::
::::Hi Thomas,
::::The output tube is the 25L6G.
::::Thanks
::::
:::::If there isn't anything wrong with the speaker, then you shouldn't replace it. If the speaker is from a specific radio, and the transformer is not on the speaker, then it is likely on the radio itself, unless someone removed it from either the speaker or the radio. Your radio will be much happier with its original electrodynamic speaker than with a new one. If the speaker is seriously damaged, though, and you don't feel that you can recone it, then you should replace it. If you mention the output tube(s) used in your radio, I can give you a rough idea on an output transformer, which you will need, regardless of what type of speaker you use. www.tubesandmore.com sells a huge variety of output transformers, and there will be one for your radio. They are also known as Antique Electronic Supply, and will send you a very interesting and informative catologue.
:::::
:::::Thomas

You're welcome. A very very good friend of mine is from Leon, Mexico. He's been here for 5 years (Milwaukee). Learned his English in college in Leon. He's very good, but still has a thick accent and occasionally messes up. That's life, and it doesn't bother me. I don't know more than perhaps 60 or 70 Spanish words, and can't say more than perhaps 15 or 20 sentences in Spanish, so anyone who can speak two languages is far better than me.

www.tubesandmore.com will ship world wide, but if you find a source down there, that's great, too. If Radio Shack has stores down there, you can try their universal public address output transformer, if they still sell them. Last year I bought one, so they must. The primary impedances are not exact matches for what you need, but it should work quite well. Use the high impedance side as the primary and the low impedance side as the secondary.

Good luck!

Thomas