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Old 19th August 2003, 08:51 AM   #1
Lucas_G is offline Lucas_G  Netherlands
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Default Building Rectifier Bridge with MUR 860

Dear PSU experts,

Peter Daniel and others have made very positive comments on using MUR 860 diodes in rectifier bridges.
That is why I am considering to replace the standard bridges in my Pass projects with selfmade MUR 860 bridges.

I would like a few suggestions as to how to build them...

On his site, Nick Whetstone gives a scheme for building such a bridge in his gainclone amp:

http://www.decdun.fsnet.co.uk/gainclone.html#gcpsu

(See picture attached here)

However, I notice that he doesn't use any heatsinks on the MUR.

1. Does this limit the current-handling?

2. I saw that these diodes are listed as 8 Ampere. Is that with or without heatsinking?

3. How does one calculate the total amount of current handling of a bridge? When using four pieces in a bridge, does that mean an overall handling capacity of 32 Ampere?

4. If I would use two bridges per channel (i.e. 8 pieces of Mur 860), would that be sufficient for use in an Aleph 2 with 220.000 uF per channel? Is any heatsinking neccesary here?

5. If one chooses heatsinking, do they need to be electrically isolated from the heatsinks?

6. Does anyone have pictures and/or descriptions on how they made heatsinked bridges with the MUR860?

Any help very much appreciated!

Regards,

Lucas.
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Old 19th August 2003, 09:07 AM   #2
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Over 2 A you need allways heatsink if the package is TO-220 or similar. Think 1 V across diode and multiply with current. 2 watts in a TO220 is hot.

I recommend that you use a diode with a rating which suits you. 8 A is little I think. Why don't you use 25 A or so? In a rectifier bridge each diode must take all the current.

But first calculate how much current the amp will draw and then deside if the amp should be used in heavy or light duty. When you know that you can deside how big the rectifier bridge you need.
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Old 19th August 2003, 01:59 PM   #3
eLarson is offline eLarson  United States
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I'd use the 8A guys for a preamp and stick
with the bigger 25A+ sizes for power
amps.

IXYS has some higher current soft
recovery bridges you might look into. I
have a couple but I haven't decided what
amp project to embark on.

Erik
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Old 19th August 2003, 04:04 PM   #4
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IR has them ,too.
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Old 19th August 2003, 06:10 PM   #5
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The heatsink mount is electrically the cathode on an 860. So don't just screw them down to some block of aluminum together willy-nilly.

I had the same issue as you about a week ago and got a variety of responses. Peter Daniels has a nice layout using four 860's, feet pointing together, mounted on fiberglass.

If they do, in fact, need a little heatsinking (not nearly as much as a power chip - lm3875 on a GC, for me) then it seemed to me that fiberglass would work like more of an insulator, not a sink.

So I tried something different. I laid them out in two flat groups of four (my gainclone has two bridges) with the feet all point toward front, and screwed them into a support of wood. Between the 860 and the wood, I sandwiched 3 aluminum washers each - little-big-little, which significantly increased the heatsink mass and surface area.

note, use alum. washers. Steel does not move the heat well at all. Also, the sandwich (screw, 860, little washer, big washer, little washer) is important, IMO, as it fits the 860 well on top and raises the "fins," if you will, of the big washer off the board for better air circ. Cost: Less than a buck.

Also, it is physically solid as a rock and grounding is not an issue. I am playing around with the idea for my 3875's also, using higher stacks of bigger, multiple-sized alum washers.

GnD
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Old 20th August 2003, 03:31 AM   #6
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Unless you make a bridged, high power gainclone or run several off the same bridge, heat sinking isn't needed. A 30 watt gainclone will never draw much more than 3 amps of dc at any given instant, which will be about .65*3 or about 2 watts out of each diode. that gets a to220 pretty hot, but if you consider the averaged power output over a few seconds of actual music (unless you listen to high power square or sine waves as entertainment), you get about 1-5% of the maximum, for the equivalent of a whopping .02-.1 watts. Dare I say that even a 1n4001 would suffice? Basically, just make them look good. It seems they sound better that way.

-Chris
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