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Old 30th March 2011, 07:05 PM   #1
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Default Graetz Field Coil

Hi there,
I have just won a lovely pair of vintage graetz BV8070 drivers for a full range OB project. The issue I have is not been certain of the appropriate voltage to apply to the field coil. I have seen it suggested that they take 100V, but at 950R that would mean 100mA, and about 10W heat - which seems excessive for this situation.
I know that often these were used in a radio and that they were used as a smoothing choke - so it that case the current and voltage would be defined by the Radio's current draw - which might be as little as 50mA or less.

Anyone got any informed ideas on this one.

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Old 30th March 2011, 07:14 PM   #2
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even if I can't help with this one , I don't mind some porn .

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Old 30th March 2011, 07:51 PM   #3
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Unfortunately they wont arrive until about a fortnight - so nothing to show yet

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Old 30th March 2011, 08:03 PM   #4
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put this one through google translate Field Coil - 20 -


look at post 497

it sez 80mA - 90mA

ZM sez - use CCS and don't care for voltage

maybe asking Kwayzee Rullit guy via e-mail will help ?

dunno anyone else looking more adequate to have ancient FC knowledge

I found pictures back - in post 405 , but I'm lurker there , so I can see pic , even if I understand Russian almost good as English
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Old 30th March 2011, 08:19 PM   #5
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Sounds a bit of a fan to me.
I heard it said that these were made in the same factory as the siemens Klangfilm drivers which go for 1000+. These ones I got for 100, so hopefully they will be something of a sleeper bargain

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Old 31st March 2011, 04:32 PM   #6
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Klangfilm KL 42006 Feldspulen Lautsprecher / Speaker bei eBay.de: Lautsprecher (endet 30.03.11 21:02:51 MESZ)
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Old 31st March 2011, 04:40 PM   #7
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Its definately not like that one. The field coil is somewhat lighter. Still I am hopeful for good things. I spoke to a man today who has quite a bit of experience on OB's with field coils and he reckoned at the cost of a bit of sensitivity I could get a better bass and tone by running them down at 50V.

I am thinking at this stage to go with an adjustable CCS arrangement with a raw 100V trimmed down to whatever voltage delivers the required 60-80mA. I feel a little more confident that I am not going to fry my new babies on first power up

Shoog
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Old 31st March 2011, 06:43 PM   #8
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whatever you do - count that ~45C on surface of FC is safe ;

don't know above , considering type of ancient glues and VC former
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Old 31st March 2011, 07:06 PM   #9
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Quote:
Originally Posted by Zen Mod View Post
whatever you do - count that ~45C on surface of FC is safe ;

don't know above , considering type of ancient glues and VC former
Going for a lower setting than many suggest should keep thing nice and cool. I wouldn't be that happy running them at 45C.We don't have to many issues with things overheating in the frigid north of Ireland

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Old 31st March 2011, 07:15 PM   #10
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no - 45C isn't that much

it's just 8C warmer than human body

edit - for illustration - just look at linked Klangbild auction

2420R FC , clearly written 250Vdc

that means scorching ~26W of dissipation .......
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