Upright Heat sinks for f5

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thunk303

thunk303

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Joined 2005
I know this has been asked a few hundred times, but hey... I really want to build a tall narrow chassis for my f5, I know upright is less efficient and therefor more expensive but I cant help myself.

Nelson says:

At 1.3 amps per channel, you will see idle heat dissipation of 62 watts. To keep the temperature rise of the heat sink to 20 deg C. above the ambient temperature, you will want a heat sink rated at about .6 deg C./watt for each transistor. An example of this would be a chunk of finned aluminum, with a series of 2” fins attached to an 8” by 6” base. You will need two per channel.

So for 1 channel I would need a 2"D x 6"W x 16"H with at least a 1/4" plate
as a minimum size.

Does anybody know of a supplier of this type of design/dimensions or an alternative that I might build myself??

Can I stack smaller sinks and link them somehow?

I am open to any suggestions no matter how weird.

Cheers all
Dean
 
A

AndrewT

R.I.P.
Joined 2004
thunk303 said:
Nelson says:.........An example of this would be a chunk of finned aluminum, with a series of 2” fins attached to an 8” by 6” base.
Click to expand...
So for 1 channel I would need a 2"D x 6"W x 16"H with at least a 1/4" plate
as a minimum size.
Click to expand...
No!
The dissipation capability of a heatsink is roughly proportional to the sqrt(height).
It is also roughly proportional to the width.

If you start with a 8"w by 6"high with the 20off 2" fins vertical, then double the heat dissipation capability comes form 16"w by 6"h with 40off 2" fins, or 8"w by 24"h with 20off 2" fins.

But, there is another factor to consider.
This assumes that the whole backplate is isothermal (all at the same temperature).
If the back plate is relatively thin compared to it's area then parts of the backplate will be much cooler than the contact spots at the heating devices.

8" by 6" with two devices near the middle has a maximum radius from device to farthest corner ~3.5" This will require a back plate ~3.5/10 = 0.35"

If you increase the backplate to 16"w then the thickness will need to be ~7.5/10 = 0.75"
Similarly for the 24"h sink, recommended thickness ~1"

Your 1/4" backplate will run very hot where the devices are mounted and run much cooler at the extremities.
 
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A

AndrewT

R.I.P.
Joined 2004
Ed LaFontaine said:
HeatsinkUSA

He has a variety of widths which he will cut to your length.
Click to expand...
A pair of 10.08" by 10" back to back with the devices clamped between will be capable of dissipating enormous power. These have 3/8 backplate and 2.5" fins
This could be for a paralleled F5 or a balanced F5, since both versions have 4devices (or even a Stereo F5). Place an N & P in contact with one sink and turn over another N & P to contact the other sink. Bolt the sinks together and mount them on a pole (pole dancing?) above the PSU and voltage stage.
 
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thunk303

thunk303

Member
Joined 2005
Nice one guys and point taken Andrew, I did ask for input on the subject and appreciate the maths. I need to look at all my options again with this info in mind.

The idea is for a taller final product, think 3-1 ratio, but considering Andrew's advice it makes sense why nobody builds amps like this.
Looking through the heatsink USA catalog now.

http://www.frigprim.com/online/natconv_heatsink.html

Did anybody have a go of this Java app, Andrew or other, does it seem like a realistic/easy way to spec a heat sink when building?

Cheers
Dean
 
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