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Old 5th June 2002, 03:20 PM   #11
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Where can I buy 0.075 ohm Caddock 916 or 930 power resistors.

The lowest I have seen at Parts Connexion or Welborne Labs is 0.1 ohm.
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Old 5th June 2002, 07:57 PM   #12
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Default Caddock current resistor

I don't thinK you need a Caddock for this. Spend money on the feedback resistors instead!

RWF-LVR3-.08 .08 ohm 1% 3w WW Resistor 3.00
http://www.surplussales.com/Resistors/WW0015-1.html

"Caddock has a .075 ohm, which would be closer to 6x.47 in parallel (about 4%, anyway).
Yes, the value matters. The formula is in the patent, but in general you want the value of the output resistor array to be half the cumulative value of the Source resistors for the current source MOSFETs"

It seems that it wouldn't hurt to use a bigger current sense resistor and change the value of the AC feedback resistor to compensate for it. Resistor values under 0.1 ohms are hard to find. Don't forget to take your feedback from as close to the resistor body as possible or your wire resistance will change the value of the resistance that the feedback in the current source is measuring across. This is a real concern for resistor values this low and some resistors come with seperate sense leads for this purpose.


H.H.
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Old 5th June 2002, 08:09 PM   #13
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That resistor is in the signal path, would 3W be enough?
I don't thing it's less important than source resistors for which you are using $40 Vishays.
How is TEX X coming? I first want to finish my Aleph 5 mono.
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Old 5th June 2002, 08:34 PM   #14
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Wink Resistors for poets

"That resistor is in the signal path, would 3W be enough?
I don't thing it's less important than source resistors for which you are using $40 Vishays."

Ah......resistor envy, it's a terible thing. Actually where it is in the signal path probably makes it little less important. 3 watts should be more than enough. (0.1 X 30 AMPS!) Many low value precision wire wounds are actually very good and I would not hesitate to use the Mills non magnetic wire wound other good wire wound for this resistor. I have plenty 0.5 ohm and 0.25 Vishays, maybe I will trade you for some other parts.

" How is TEX X coming? I first want to finish my Aleph 5 mono."

Finish the Aleph 5s first, maybe we should wait for Grey. It is a lot of work and I am gathering parts as I build, I know it will not look as nice as yours though and will listen to it in the dark. Some joker out here will probably blind side all three of us!

H.H.
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Old 5th June 2002, 09:34 PM   #15
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If you're interested in Caddock parts, but can't find the values you want at retail, Caddock will sell directly to the public. www.caddock.com
They've got more values than you can shake a stick at, but they aren't exactly cheap. However, they are one of the best resistors out there. I seem to recall that Erno Borbely prefers them to Vishay; says they're more neutral.

Grey
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Old 6th June 2002, 03:04 PM   #16
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When mounting MOSFETs on an anodized heatsink, is there any reason to use a mica insulator?

I would assume that it would be better to mount the MOSFET with thermal grease only, since the surface of the heatsink is NOT electrically conductive (have double checked with VOM). That being said, in the past I have had a MOSFET go bad when I was probing (and probably touched an anodized heatsink of a MOSFET without a mica insulator).
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Old 6th June 2002, 03:28 PM   #17
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Exclamation mounting MOSFETs on an anodized heatsink

I would not do this! The anodized layer is pretty thin and a high point in the aluminum or transistor case, a scatch, a void in the anodizing ,or a small chip of metal from drilling or deburing any holes could punch through the anodized layer when the transistor is screwed down snuggly. I really think this begging for trouble and it won't take long to find it.

H.H.
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Old 6th June 2002, 05:17 PM   #18
jam is online now jam  United States
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Mark,

One way is to do this is to isolate the heatsink from the chassis and use seperate heatsinks for n and p channel devices.

Jam

P.S. Brittany Spears might not like this idea.
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Old 6th June 2002, 06:11 PM   #19
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Red face Brittany Spears might not like this idea

She says you wait till your married, but if you just can't wait to use protection, a girl has got to be careful..... Use the Mica washers. Live heat sinks are asking for a different problem, like the first time someone accidently touches a speaker wire to a sink with power supply voltage on it. Jam is just trying to see if I am paying attention..... Shame on you jam!!
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