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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 15th September 2019, 06:09 PM   #28961
jneutron is offline jneutron  United States
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I had no idea how hard ferrite is. My bandsaw couldn't touch it. Gasket off, surround detached, basket off magnet, front plate removed and cut in two.

First tried cutting faceplate on magnet. Don't bother, trying to clean iron filings from a gap with more than a tesla field....no way. So used a chisel to pop the epoxy holding the faceplate, cleaned it all up.

Next, detach of spider. I will try chemistry first, I recall Ed mentioning gum out carb cleaner. Basket mounting surface deformed when I detached it from faceplate, so I have to flatten that. I will use 2 mil nomex insulator between magnet and faceplate if ferrite conducts. If not, epoxy. Basket will have insulation to the faceplate, was thinking 10 oz glass cloth with epoxy.

Will sweep bare vc tomorrow as well.

Jn
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Old 15th September 2019, 07:13 PM   #28962
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part III
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Originally Posted by jneutron View Post
if ferrite conducts.
I have tried many times with Ohm meters, they show open circuit.
I havenít used a high voltage insulator tester though

George
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Old 15th September 2019, 08:49 PM   #28963
RNMarsh is offline RNMarsh  United States
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Originally Posted by Bonsai View Post
Best wishes in your move Richard. Trust it goes smoothly and you enjoy your tome over there. I spent 10 years in Asia and still get a hankering to go back. Awesome experience - I consider myself very lucky.

Thank you --- 10 years is long enough to begin to know it in some depth. It is very different... almost extreme compared to western culture. But, I am long over the culture shock. Been going there 20 or so years. Feels like home now.

-Richard

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Originally Posted by Ultima Thule View Post
Moving away from muricah' for good sounds so dramatic, is the 4th Reich about to collapse.. anyway hope your kidneys situation are in checks and balance, you might want to look into how to possibly reverse the situation with a holistic approach and that includes stage 5. Enjoy your new life Richard.

Cheers Michael
IMO it has collaspsed a long time ago. The party is over. Burnt toast here.

Kidney situation is a question mark. At my age, 12 more years is the end of it for most people anyway and I can nurse this kidney that long.

Most people dont know what will cause their death... only that you Will die. Its a big surprise awaiting you at the end. In my case, i already know so nothing to worry about.

Onward and upward... more learning to do, more adventures to have. More help and love to give. Got to hang in for my girl (well, looks more like a woman now). See her get launched into an engineering career. So I am positioning myself to help her and be more often able to visit -- being closer. She will stay in Asia.. maybe Thailand after she her EE degree. USA refused her admit into country in USA 3 times. Done trying. Its basically, because she comes from poor family in poor country. Subsistence farmers. Dont care if she got max SAT score possible in math and 160 IQ and top grades.

Old world Sarada / New world Sara.

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THx-Richard
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Old Yesterday, 03:54 AM   #28964
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part III
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Originally Posted by RNMarsh View Post
IMO it has collaspsed a long time ago. The party is over. Burnt toast here...
THx-Richard
I wish you the best in your new digs, Richard, I hope the move is invigorating and look forward to hearing from you here !

Best regards,
Howie
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Old Yesterday, 05:52 AM   #28965
RNMarsh is offline RNMarsh  United States
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I wish you the best in your new digs, Richard, I hope the move is invigorating and look forward to hearing from you here !

Best regards,
Howie
Thank you.... and if you need some amps, power products, dac... what ever just email me with request.

rmarsh@calweb.com

-Richard
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Old Today, 02:22 AM   #28966
gerhard is offline gerhard  Germany
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Originally Posted by gpapag View Post
I have tried many times with Ohm meters, they show open circuit.
I havenít used a high voltage insulator tester though
George
I have heard of glowing orange ferrite beads having ground contact. (from a friend)
It depends on the material.

regards, Gerhard
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Old Today, 02:34 AM   #28967
phase is offline phase  United States
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Thatís very commendable to support your family with a move like that, should be a win-win it sounds like.
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Old Today, 03:11 AM   #28968
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part III
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Originally Posted by gerhard View Post
I have heard of glowing orange ferrite beads having ground contact. (from a friend)
It depends on the material.

regards, Gerhard
In a properly matched RF system there will be no current flowing on the outside of the coax, just on the inside of the shield and outside surface of the inner conductor. When ice damages a broadcast antenna system and causes a severe mismatch, it can cause high common mode currents to flow. In these cases I have seen common mode chokes (which attenuate exterior coax shield currents) made using ferrite cores get hot enough to melt their plastic enclosures.

This is not due to their electrical conductivity though, just their resistance to induced flux.

Howie
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Old Today, 03:44 AM   #28969
keantoken is offline keantoken  United States
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Originally Posted by hhoyt View Post
This is not due to their electrical conductivity though, just their resistance to induced flux.

Howie
So you are saying there is some way to produce heat from flux modulation that does not involve electrons? It could mechanically generate heat but you are saying it's a resistance to the induced flux as though that is the only thing.

The problem here is that the induced choke voltage is on the imaginary axis, so there can't be any power flow unless there is something in the magnetic loop converting flux modulation back to the imaginary axis (so it can be converted to real axis EMF). In the case of speakers, that is the motion of the coil through the flux. In the case of induction stoves, it is the magnetic inductivity of the pot (magnetic inductivity corresponds to cartesian conductance).

In a magnetic material the skin depth does not have to be smaller than the part in order for it to heat up. Even then the heat output is still proportional to power input. So you just need a very high AC current. IIRC ferrite is sintered, so while it may not be conductive between grains, the grains themselves could be conductive enough to have significant eddy currents. Since they are physically small, the skin depth may exceed their size. This only means that their shunt inductance will be small, so there will be little apparent change in inductance of the core, just the presence of a shunt resistance.
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Last edited by keantoken; Today at 04:11 AM.
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Old Today, 04:59 AM   #28970
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part III
Quote:
Originally Posted by keantoken View Post
So you are saying there is some way to produce heat from flux modulation that does not involve electrons? It could mechanically generate heat but you are saying it's a resistance to the induced flux as though that is the only thing.

The problem here is that the induced choke voltage is on the imaginary axis, so there can't be any power flow unless there is something in the magnetic loop converting flux modulation back to the imaginary axis (so it can be converted to real axis EMF). In the case of speakers, that is the motion of the coil through the flux. In the case of induction stoves, it is the magnetic inductivity of the pot (magnetic inductivity corresponds to cartesian conductance).

In a magnetic material the skin depth does not have to be smaller than the part in order for it to heat up. Even then the heat output is still proportional to power input. So you just need a very high AC current. IIRC ferrite is sintered, so while it may not be conductive between grains, the grains themselves could be conductive enough to have significant eddy currents. Since they are physically small, the skin depth may exceed their size. This only means that their shunt inductance will be small, so there will be little apparent change in inductance of the core, just the presence of a shunt resistance.
In an ideal magnetic material there is no loss, but in practical ferrite materials, there is hysteresis loss as well as what you state, eddy current losses. Many MnZn ferrites (mix 31, 75) have relatively low bulk resistivities, mix 31 for example is specified at 3000 ohms per cm^3.

Cheers,
Howie
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