Has anybody ever substituted a permanent magnet for a field coil?
The field coil is several thousand feet of #28 or #30 enameled magnet wire, so rewinding is out ot the question, at least for me. The "open" is not anywhere near the connections, so no simple fix presents itself.
Doug
You need to do two things. If the field is in series with the power supply you need to replace it with a choke/resistor or resistor/electrolytic cap combination. A resistor alone will allow more hum so filter cap values will ptrobably need to be increased.
The speaker needs a magnet. Try putting a permanent magnet in the center of your speaker. Computer hard drives have very strong magnets. You should be able to get one of these magnets to work.
Something I haven't tried but will work is winding fewer turns of heavier wire for the field. Build a 6 volt or so supply to power the electromagnet.
Norm
:I have a Majestic electrodynamic speaker with an open field coil. Otherwise, the speaker is in good shape, and I want to salvage it if possible.
:
:Has anybody ever substituted a permanent magnet for a field coil?
:
:The field coil is several thousand feet of #28 or #30 enameled magnet wire, so rewinding is out ot the question, at least for me. The "open" is not anywhere near the connections, so no simple fix presents itself.
:Doug
I will keep your idea for a separate, high-current power supply in reserve.
By the way, I figure the original field winding has about 7,000 ft of #30 wire and about 490 amp-turns (@ 55mA). At 1-A, just for example, I'd only need about 27 turns! The approach I would try is to build a current supply, not a voltage supply. Comments?
Doug
:Hi Doug
:
: You need to do two things. If the field is in series with the power supply you need to replace it with a choke/resistor or resistor/electrolytic cap combination. A resistor alone will allow more hum so filter cap values will ptrobably need to be increased.
:
: The speaker needs a magnet. Try putting a permanent magnet in the center of your speaker. Computer hard drives have very strong magnets. You should be able to get one of these magnets to work.
:
: Something I haven't tried but will work is winding fewer turns of heavier wire for the field. Build a 6 volt or so supply to power the electromagnet.
:
:Norm
:
:
::I have a Majestic electrodynamic speaker with an open field coil. Otherwise, the speaker is in good shape, and I want to salvage it if possible.
::
::Has anybody ever substituted a permanent magnet for a field coil?
::
::The field coil is several thousand feet of #28 or #30 enameled magnet wire, so rewinding is out ot the question, at least for me. The "open" is not anywhere near the connections, so no simple fix presents itself.
::Doug
You are right. It's amp turns that count. That what makes it nice about lower voltage, heavier wire but much fewer turns. In this case you could use a 6 volt supply at 1 amp. If you need 490 amp turns it takes 6 volts @ 1 amp with 82 turns. Still much better than 7000 feet of thin wire.
Norm
Thanks, Norm. I'm going to try adding a permanent magnet. All Electronics has several surplus neodymium magnets that I think should fit my speaker's geometry. (I don't have a sacrificial hard drive to canibalize magnets from, but the magnets I'm intending to buy are pretty cheap.)
:
:I will keep your idea for a separate, high-current power supply in reserve.
:
:By the way, I figure the original field winding has about 7,000 ft of #30 wire and about 490 amp-turns (@ 55mA). At 1-A, just for example, I'd only need about 27 turns! The approach I would try is to build a current supply, not a voltage supply. Comments?
:Doug
:
::Hi Doug
::
:: You need to do two things. If the field is in series with the power supply you need to replace it with a choke/resistor or resistor/electrolytic cap combination. A resistor alone will allow more hum so filter cap values will ptrobably need to be increased.
::
:: The speaker needs a magnet. Try putting a permanent magnet in the center of your speaker. Computer hard drives have very strong magnets. You should be able to get one of these magnets to work.
::
:: Something I haven't tried but will work is winding fewer turns of heavier wire for the field. Build a 6 volt or so supply to power the electromagnet.
::
::Norm
::
::
:::I have a Majestic electrodynamic speaker with an open field coil. Otherwise, the speaker is in good shape, and I want to salvage it if possible.
:::
:::Has anybody ever substituted a permanent magnet for a field coil?
:::
:::The field coil is several thousand feet of #28 or #30 enameled magnet wire, so rewinding is out ot the question, at least for me. The "open" is not anywhere near the connections, so no simple fix presents itself.
:::Doug
Something didn't sound right. That would be 490 turns @ 1 amp. Still a lot less than a mile of wire.
Norm
:Doug
:
: You are right. It's amp turns that count. That what makes it nice about lower voltage, heavier wire but much fewer turns. In this case you could use a 6 volt supply at 1 amp. If you need 490 amp turns it takes 6 volts @ 1 amp with 82 turns. Still much better than 7000 feet of thin wire.
:
:Norm
:
:Thanks, Norm. I'm going to try adding a permanent magnet. All Electronics has several surplus neodymium magnets that I think should fit my speaker's geometry. (I don't have a sacrificial hard drive to canibalize magnets from, but the magnets I'm intending to buy are pretty cheap.)
::
::I will keep your idea for a separate, high-current power supply in reserve.
::
::By the way, I figure the original field winding has about 7,000 ft of #30 wire and about 490 amp-turns (@ 55mA). At 1-A, just for example, I'd only need about 27 turns! The approach I would try is to build a current supply, not a voltage supply. Comments?
::Doug
::
:::Hi Doug
:::
::: You need to do two things. If the field is in series with the power supply you need to replace it with a choke/resistor or resistor/electrolytic cap combination. A resistor alone will allow more hum so filter cap values will ptrobably need to be increased.
:::
::: The speaker needs a magnet. Try putting a permanent magnet in the center of your speaker. Computer hard drives have very strong magnets. You should be able to get one of these magnets to work.
:::
::: Something I haven't tried but will work is winding fewer turns of heavier wire for the field. Build a 6 volt or so supply to power the electromagnet.
:::
:::Norm
:::
:::
::::I have a Majestic electrodynamic speaker with an open field coil. Otherwise, the speaker is in good shape, and I want to salvage it if possible.
::::
::::Has anybody ever substituted a permanent magnet for a field coil?
::::
::::The field coil is several thousand feet of #28 or #30 enameled magnet wire, so rewinding is out ot the question, at least for me. The "open" is not anywhere near the connections, so no simple fix presents itself.
::::Doug
Doug,
What model Majestic? I might have a good speaker.
Jon.
:Doug,
:What model Majestic? I might have a good speaker.
:Jon.
Doug, This is your lucky day. I have the complete set minus tubes and the speaker is good. If you want it, its yours. I have been trying to give it away for a couple of years, no one wants it. I live in Louisville Ky. Let me know if and what you want and we can work out the details.
Jon.
:
::Doug,
::What model Majestic? I might have a good speaker.
::Jon.
::Hi, Jon. The radio is a Model 90-B. The speaker is a Majestic Super-Dynamic, Model G-3.
::Doug
:
:Doug, This is your lucky day. I have the complete set minus tubes and the speaker is good. If you want it, its yours. I have been trying to give it away for a couple of years, no one wants it. I live in Louisville Ky. Let me know if and what you want and we can work out the details.
:Jon.
::
:::Doug,
:::What model Majestic? I might have a good speaker.
:::Jon.
If you ever do wish to rewind a Majestic, all you really need to do is buy a big spool of wire. Every time I rewind a motor, I go to a wire supply place, and they hook me up with about a 10 or 20 lb spool of wire. The field coil of the Majestic is about the same size and weight as one of these spools of wire! It's HUGE! Actually, I think I have a spool of #26 wire. I can't remember what the gauge is of the speaker field, but it's close.
Actually, I've been having unbelievable luck. I bought the Majestic on Saturday for $50. I unloaded it on Sunday without throwing out my back (although I had to disassemble it first). The first thing I checked was the speaker, which had an open field coil. Jury-rigged a temporary speaker, and the set works fine! Jon comes up with a replacement field coil on Monday.
I ought to buy a lottery ticket today before before midnight. (With my current luck, I should only need one ticket!)
Doug
:Sad that none wants those radios. They are fine radios.
:
:If you ever do wish to rewind a Majestic, all you really need to do is buy a big spool of wire. Every time I rewind a motor, I go to a wire supply place, and they hook me up with about a 10 or 20 lb spool of wire. The field coil of the Majestic is about the same size and weight as one of these spools of wire! It's HUGE! Actually, I think I have a spool of #26 wire. I can't remember what the gauge is of the speaker field, but it's close.
:
:
T.
I agree-these are great radios.I have both a model 90, 90B and a model 20 lowboy. Thay are built like a Mosler safe and have fantastic sound.If anyone needs parts for a 90-B I have the rest of the speaker parts, power supply and chassis that is not frozen,knobs, dial bezel etc. I would rather give away or trade. Unfortunatly someone chopped off the legs and the rest of the cabinet is pretty far gone.
Jon.
I wish I could start a trend so that people would go nuts over these radios like they do over simple catalin radios. These radios are masterpieces (majestic in every way), and people just part them out and throw them away. I suppose up-ing the desirability will further up the price of '45 and '50 tubes, though. Sad for me.
....Also, I guess they don't quite have the striking appeal of a catalin radio or a streamlined radio of the 30s, but they are beautiful and well made. The audio quality could easily compete with some of to-day's radios. Amazing for 80 year old technology.
Glad that you and other people on this site work with these sets. They are wonderful.
T.