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City: Lancaster
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I have a Model 570 Grandfather Clock. The speaker has an open field coil, which I see is a common problem with the Model 70. I've seen some of the options, but I still have a bunch of questions. I would prefer to keep the original Philco speaker, but it's not mandatory.
1. The Field Coil is inside a pressed on metal form. With my available equipment and ability, I would end up destroying the speaker attempting to remove/replace the coil. Is there anyone that does this at a reasonable cost? I have rewound coils, but they were easily removed.
2. I have a Rola 8" speaker that would possibly work, but the Field Coil is 1400 ohms, not the 3100 ohms that the original speaker has. I don't know the voltage across the original coil, to be able to determine what fixed resistance/wattage to use with the 1400 ohm coil. I assume a 1700 ohm fixed resistor, but what wattage?
I just got started looking at the set and had a bad #47 tube. The transformer looks to be good with all voltages in reason. The Audio transformer is also OK. I haven't checked the IF coils yet, but have my fingers crossed. If good, then I will proceed with the normal re-cap and out-of-spec resistor replacement.
Thanks
John N3MUN
(This post was last modified: 08-13-2023, 08:00 AM by
jjfritz5528.)
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For #3, place an ad in the Wanted section of this Phorum. Ads are not allowed in the discussion forums. Thanks.
(these come up for sale on eBay frequently)
Posts: 7,214
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City: Roslyn Pa
Think the field coil removal goes something like this.
Remove spkr cone. Face spkr front down onto flat surface. Find a small 3/8 drive socket. Place the small end of the socket over the spkr pole. Must not be larger than the pole. Attach gear puller to the u shaped that holds the pole in place. Screw the gear puller's bolt into the back of the socket till it presses the pole out. Once the pole is out remove the field coil.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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City: Lancaster
State, Province, Country: PA
Radioroslyn-
I'm a rookie at this process. I will need to get a gear puller. Obviously I have never removed one like this. I'm nervous about removing the cone. Do you know if there are any write-ups or YouTube videos on this part of the process? I assume that the cone can easily be re-installed after the new coil is wound? I just wound one for another speaker that was 1300 ohms. This is 3200, not sure what gauge wire should be used, but I used #36AWG on the previous one.
Sorry for all the questions. Just don't want to end up with a pile of junk that used to be a speaker due to my lack of expertise.
Thanks in advance!
Thanks
John N3MUN
Posts: 7,214
Threads: 266
Joined: Dec 2009
City: Roslyn Pa
Cone is easy to remove. Unsolder wires (2) from voice coil to output transformer. The wires maybe held in place by a small coil/spring. Carefully lift the wire up to release them from this coil with a pair of needle nose pliers. Unscrew the screw in the center and then the screws around the circumference of the speaker's frame. You maybe able the lift the cardboard spacer without it sticking or tearing the cone. If not what you do is take an Xacto or small snap blade knife between the cone and the frame. The object is separate cone from the frame and keeping the cone intact. Once the cone is loose from the frame lift it straight out.
If the spider and voice coil are in good condition I've reused them with a new cone. Generally the old cones are pretty beat after 90yrs. Paper is dry a brittle. You can use some diluted fabric glue around the flex area along the outside edge. This will bolster it up for a while.
< Do you know if there are any write-ups or YouTube videos on this part of the process?
There was a fellow here on the Phorum that had one of those style spkrs. He rewound the FC and OPT. The posts are for the Phorum but I'm not sure how to find them. I think it was a couple of yrs ago. Don't know of any videos.
< I assume that the cone can easily be re-installed after the new coil is wound?
The cone/vc just screws back in. There is some gluing if you end up replacing the cone. You just have to remember to make sure to aim the vc wires towards the opt.
< not sure what gauge wire should be used, but I used #36AWG on the previous one
Well I'm not sure either. But this we know the fc current rating is 40ma. So you can use that as a minimum rating to determine gauge. Or use a micrometer to check the size of the wire of the open coil. Then you can figure the ohms per foot. Larger the gauge the longer the wire the bigger the coil.
https://philcoradio.com/phorum/showthread.php?tid=22316
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
