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Thread: My new pickup magnetizer

  1. #36
    Old Timer J M Fahey's Avatar
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    Thanks.
    Hereīs a couple, the standard day to day breadwinners:
    G12 side by side with a Celestion Greenback for comparison.
    Of course I usually sell mine inside cabinets, or to fellow ampmakers, so didnīt care too much about fancy covers or even labels, or pretty color schemes, they're quite utilitarian:


    Same from back:


    One workday product:


    Already zinc plated frames, waiting for the ceramic magnets, polepiece and backplate.
    Forward stack 10" frames, back ones 12" in different versions (A Jensen type and a Celestion type) :

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    Thanks.
    Hereīs a couple, the standard day to day breadwinners:
    G12 side by side with a Celestion Greenback for comparison.
    Of course I usually sell mine inside cabinets, or to fellow ampmakers, so didnīt care too much about fancy covers or even labels, or pretty color schemes, they're quite utilitarian:


    Same from back:


    One workday product:


    Already zinc plated frames, waiting for the ceramic magnets, polepiece and backplate.
    Forward stack 10" frames, back ones 12" in different versions (A Jensen type and a Celestion type) :

    Cool stuff gotta try them someday
    We build guitars hansen mostly relic stuff, I have been designing pickups for 5 years now, came from a electronics background... I think they sound good now

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  3. #38
    Old Timer J M Fahey's Avatar
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    Hey !!!! Cool guitars!!!
    And find incredibly accurate the "aging" process.
    You donīt own a Time Machine, do you?

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    Juan Manuel Fahey

  4. #39
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    Quote Originally Posted by J M Fahey View Post
    Hey !!!! Cool guitars!!!
    And find incredibly accurate the "aging" process.
    You donīt own a Time Machine, do you?
    Thanks we do our best.. Yes we have a time machine
    Have a nice weekend
    Claus

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  5. #40
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    Mechanical drawing with mesurements nearly done..
    Click image for larger version. 

Name:	Magnetizeryokes.jpg 
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  6. #41
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    Mechanical drawing with mesurements.....

    Click image for larger version. 

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    Hope you can use them..

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  7. #42
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    Another one...
    Click image for larger version. 

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    Happy xmas
    Claus

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    Hi Claus

    Do you use any kind of mild steel for the poles or do you have a particular requirement for pure iron ?

    Cheers


    Andrew

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    Would ferrite work? Soft, aka electrical iron is hard to come by. Maybe 1010 will be close enough.

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  10. #45
    Old Timer J M Fahey's Avatar
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    1010 is perfect.

    Ferrite has much lower saturation point, and "stays magnetized" so as soon as you turn current off "it works against you" .

    In fact 1010 is hard to get by, being so despised (for its mechanical properties) so in practice 1018 is an acceptable substitute if you can get nothing milder.

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    1010 is perfect. ... In fact 1010 is hard to get by, being so despised (for its mechanical properties) so in practice 1018 is an acceptable substitute if you can get nothing milder.
    I agree, and would add only that one can if necessary improve 1018 magnetically by completely annealing it, which is easily done.

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  12. #47
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    What about "CL-40" cast iron rod? Rod Cast Iron CL 40 1 in Dia x 3 ft L G1232533 | eBay
    Zoro is actually a great place to deal with. Good prices and free almost overnight UPS shipping +20% off coupons in the mail. They are somewhere between McMaster Carr and Graingers

    *Edit -this is "grey iron" which has a magnetic permeability of 125 vs 150 for mild steel. I have a feeling that a "Malleable Iron" would be better. See: http://www.ductile.org/didata/Sectio...c%20Properties

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    Last edited by David King; 12-12-2014 at 06:50 PM.

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    Quote Originally Posted by David King View Post
    What about "CL-40" cast iron rod? Rod Cast Iron CL 40 1 in Dia x 3 ft L G1232533 | eBay
    Zoro is actually a great place to deal with. Good prices and free almost overnight UPS shipping +20% off coupons in the mail. They are somewhere between McMaster Carr and Graingers

    *Edit -this is "grey iron" which has a magnetic permeability of 125 vs 150 for mild steel. I have a feeling that a "Malleable Iron" would be better. See: Ductile Iron Data - Section 5
    Cast iron isn't very good magnetically compared with mild steel.

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    Quote Originally Posted by Joe Gwinn View Post
    Cast iron isn't very good magnetically compared with mild steel.
    I think any mild steel will work fine.. Have not tried anything other then that we have now, not sure of the exact alloy, will try to find out, what it is.. Cast iron will not be good..

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    Last edited by Claus H; 12-12-2014 at 08:49 PM.

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    Thanks, 1018 is available everywhere and can be annealed in hydrogen (1600šF for 1 hour) to improve magnetic properties.
    This place specializes in low carbon magnetic alloys in case anyone wants to do better. CMI Specialty Products, Inc. |
    They are located in CT...
    I read through this thread which explains all about what we are wanting to know.
    Any low carbone steel dealer in USA - Magnetic engineering - Eng-Tips

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    Quote Originally Posted by David King View Post
    Thanks, 1018 is available everywhere and can be annealed in hydrogen (1600šF for 1 hour) to improve magnetic properties.
    For most purposes, any full anneal will do - the hydrogen isn't needed. Protect the piece from excessive oxidation by wrapping it in heat treating stainless steel foil, with a bit of paper inside the foil packet. Put packet in furnace, heat to a good red heat, allow to cool slowly. People used to do this in a charcoal fire. The workpiece will change shape in annealing as the strains are relieved. Anneal the raw stock, and then machine the resulting annealed piece as needed.

    For the record, the hydrogen is provided in the form of ammonia vapor fed into the furnace. The heat disassociates the ammonia into hydrogen and nitrogen.

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    I got a price from CMI Specialty iron today. A 10 foot, 1" rod costs $263+ shipping. I'd say that was a deal stopper for a few percent improvement in efficiency over CRS which runs about 1/20th that much.
    I live close to Stack Annealing, I'll call them and see what a small load of CRS pieces would cost to heat treat.

    Perhaps there would be interest in making up a kit? It would include rough machined metal parts and perhaps the electronic components. Folks can go out and buy their own coil wire, wind and assemble at home and stuff it all in a box or in the back of a Variac's case.

    Would a 1kVA variac cover this application? http://www.ebay.com/itm/1KVA-Power-T...-/321290437553

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    Last edited by David King; 12-17-2014 at 03:27 AM.

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    Hi Klaus

    Could you upgrade the circuit diagram with the specifications for the the bridge rectifier and wattage ratings of the resistors for dummies like me.

    Cheers

    Andrew

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    Quote Originally Posted by David King View Post
    I got a price from CMI Specialty iron today. A 10 foot, 1" rod costs $263+ shipping. I'd say that was a deal stopper for a few percent improvement in efficiency over CRS which runs about 1/20th that much.
    I live close to Stack Annealing, I'll call them and see what a small load of CRS pieces would cost to heat treat.
    I'd also determine if annealing is needed, or is it cheaper to use a slightly larger polepiece made of as-received 1018.

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    Quote Originally Posted by Claus H View Post
    It's two coils wired in series, two coils of 4000 turns of 0.4mm wire, on a 150mm long, 25mm diameter, soft iron core, powered from a full-wave rectifier bridge of the variac, a few tricks to get the digital readout working. Schematic comming up.. It's all build into variac case..
    What's the value for the rectifier & which variac did you used?

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    I used a 750watt variac, and a 1000v 10A rectifier..

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    Quote Originally Posted by Claus H View Post
    I used a 750watt variac, and a 1000v 10A rectifier..
    Thanks Claus

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    Quote Originally Posted by Claus H View Post
    Are there 2 full wave bridge rectifiers?

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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by Chasin' Note View Post
    Are there 2 full wave bridge rectifiers?
    Looks like 1 for the control circuit and one for the coil. This eliminates the "trying to switch D.C." problem mentioned earlier.

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    Here's my homemade magnetizer:

    Click image for larger version. 

Name:	mag.JPG 
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ID:	52492

    It is built from a 1.5kVA, 400V/230V transformer having a U/I core. A had to rearrange the laminations to have all the U shaped ones on one side and wired the coils in series. It is powered from a 30V/10A regulated power supply (seen at left). For demagnetizing I connect it to a variac.

    Works great for all alnicos.

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    Looks a little dangerous without an enclosure

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    Last edited by Chasin' Note; 02-13-2019 at 03:16 PM.

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    Old Timer J M Fahey's Avatar
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    Excellent
    Congratulations.

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    Juan Manuel Fahey

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    Senior Member LtKojak's Avatar
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    Quote Originally Posted by Helmholtz View Post
    Here's my homemade magnetizer:

    Click image for larger version. 

Name:	mag.JPG 
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ID:	52492

    It is built from a 1.5kVA, 400V/230V transformer having a U/I core. A had to rearrange the laminations to have all the U shaped ones on one side and wired the coils in series. It is powered from a 30V/10A regulated power supply (seen at left). For demagnetizing I connect it to a variac.

    Works great for all alnicos.
    It looks massive! And dangerous, even if it shouldn't be.

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    Pepe aka Lt. Kojak
    Milano, Italy

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    Quote Originally Posted by LtKojak View Post
    It looks massive! And dangerous, even if it shouldn't be.
    ? Why dangerous?

    It's just a coil (an electromagnet) driven by <30VDC. Just don't forget the freewheeling (snubber) inverse diode at the DC power supply terminals. A regulated supply isn't really necessary, but I had it and it gives me great control and reproducibilty of results.

    For demagnetizing with up to 240VAC I use safety plugs and an isolating variac.

    Didn't build it for looks, just was the easiest way for me. The core size perfectly fits all PU magnets.

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    Last edited by Helmholtz; 02-15-2019 at 06:17 PM.
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    At 30VDC and with a snubber to catch the field collapsing it's about as dangerous as a doorbell. I would like to know how you got the Es and Is apart, and out of the coil. Aren't they interleaved/alternated and all stuck together? Big step-up/ step-down xformers are often cheap on eBay. I have a 9KVA 3 phase 208-400VAC that runs one of my lathes and that was only $180 delivered for 100 pounds of iron and copper.

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    Quote Originally Posted by David King View Post
    At 30VDC and with a snubber to catch the field collapsing it's about as dangerous as a doorbell. I would like to know how you got the Es and Is apart, and out of the coil. Aren't they interleaved/alternated and all stuck together? Big step-up/ step-down xformers are often cheap on eBay. I have a 9KVA 3 phase 208-400VAC that runs one of my lathes and that was only $180 delivered for 100 pounds of iron and copper.
    Yes, the core laminations were interleaved/alternated. But there was only a thin layer of varnish at the outside surface. Some of the lamination came off easily and for the rest I used a razor blade to separate them. Was kind of awkward and time consuming but worth the trouble. Found two of these transformers in the trash bin of my former company. You want a U/I (just 2 legs not 3 leg E/I) core.

    Something like this:
    https://www.ebay.com/itm/Platthaus-5...WeA73#shpCntId

    But I can't judge if the core separates easily or if it is vacuum impregnated.

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    Last edited by Helmholtz; 02-15-2019 at 11:14 PM.
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