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Old 20th February 2012, 07:49 PM   #1311
6L6 is online now 6L6  United States
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Quote:
Originally Posted by vmcfer View Post
Does anybody an address to buy PCB's to build the Aleph-X amplifier at a correct price?
I believe that Peter Daniel has just made another batch of Aleph J-X boards available.

Contact him through his website here -- DIY Chip Amplifier Kits, PCB's, Components and Information.
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Old 20th February 2012, 07:57 PM   #1312
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Originally Posted by john65b View Post
The heatsinks fins should be parallel to the airflow rising against it like a chimney.

The Black anodizing allows more radiative heat transfer to environment, but is dwarfed by the conductive heat transfer to air at these amp temps. Once you get into very high temps (1000F) then radiative starts to govern and really matter. When Radiative heat transfer is high enough, your bare skin will feel the heat, like sitting next to a campfire.
^^ this

i understood the description as the fins ridges were pointing vertical, rather than the standard way so the length of the fin ran vertical, if you know what i mean. he was half way there, but not all the way unless i misunderstood
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Old 20th February 2012, 09:53 PM   #1313
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Originally Posted by jerfer View Post
so there is no real C/W-effect with black anodizing?
Wait a year.
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Old 20th February 2012, 11:29 PM   #1314
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You went over my head Jacco...it won't be the first time, tho...

Quote:
so there is no real C/W-effect with black anodizing?
Compared to overall conductive and convective heat transfer, this is correct...some may disagree...
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Last edited by john65b; 20th February 2012 at 11:32 PM.
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Old 21st February 2012, 01:35 AM   #1315
jerfer is offline jerfer  Canada
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Quote:
Originally Posted by qusp View Post
^^ this

i understood the description as the fins ridges were pointing vertical, rather than the standard way so the length of the fin ran vertical, if you know what i mean. he was half way there, but not all the way unless i misunderstood
You understood correctly. What I was trying to describe was a structure where the heat rises up a chimney and draws cool air from underneath. Something like this (excuse the crude drawing):

Click the image to open in full size.

The basic principle is the hot air within the heatsink/chimney structure want to escape out the top of the chimney. As this hot air escapes it draws in cool air from the sides of the heatsink that are open. These sides are normally the top and bottom of the heatsink when it is mounted more traditionally, i.e. you can see through them between the fins.

This technique is used in buildings where you want to take advantage of passive ventilation instead of pumping air through the structure using fans. I thought it may be applicable in this situation since the temperature differential is so high that you can create quite a high airflow with a reasonably short chimney.

In any case, I was just throwing the idea out there in case anyone had tried it and discounted it.

Regarding my transformer question, though, would a 20V transformer (dual secondary) produce over 24V if configured with CL-60 in series with its primaries, individual diodes for rectification (two bridges, one per rail) and CRC for filtering. Better yet, what values should I use in PSUD for:
(an explanation of how you derived these values would be great!)
  • HFA25PB60PBF diodes
  • Antek 8420 transformer
  • The current draw for the current sink

Thanks!
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File Type: jpg StackEffectHeatsink.jpg (37.4 KB, 870 views)
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Old 21st February 2012, 01:37 AM   #1316
jerfer is offline jerfer  Canada
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Originally Posted by jacco vermeulen View Post
Wait a year.
I'm afraid I don't understand. Can you explain?

Thanks,
Jerry
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Old 21st February 2012, 01:41 AM   #1317
jerfer is offline jerfer  Canada
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Originally Posted by john65b View Post
Compared to overall conductive and convective heat transfer, this is correct...some may disagree...
Thanks, John. Counter-intuitive, I guess, since you would assume that emissivity is important in actually transferring the heat away from the aluminum to the surrounding air. This is good, though, since silver is more acceptable to my other half...

Take care,
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Old 21st February 2012, 12:51 PM   #1318
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Quote:
Originally Posted by jerfer View Post
afraid
Anodizing is basically just rapid corrosion of aluminum, making the oxidation layer multiple times thicker than the natural protection skin.
Thermal conductivity of the oxide film is much lower than blank aluminum, so clean aluminum with a fresh oxide tan will be a better heatsink.

Aluminum corrosion doesn't stop, the oxide layer grows, e.g. due to sulphur content in the air.
Thickening rate is very slow though, so slow that even salt water (chloric) alloy hull boats can do without the paint job.
When i visited the marina last week i checked out the hull of an Ovni boat for pitting, stood on a cradle for the winter, example picture :
http://1.bp.blogspot.com/_ExteyBqJgY...0/IMG_0876.JPG

Anodizing does more than adding a fat oxide jumpsuit over the heatsink, the surface is dyed by filling the pores in the corrosion layer, then it's sealed.
The oxide layer of plain aluminum is not sealed, growth of the corrosion layer may be extremely small in a year's time, but the pores can hold on to particles.
See e.g. lubrication of aluminum.
Heatsinks for fan blown setups are by standard non-anodized, become very dirty in time, and are difficult to clean.
I favor blown setups, can easily extract a thousand watts heat from a 8" x 5" cross section blower heatsink.
Me cheapskate, so i buy used thyristor duty heatsinks, prepping them for an audio career after retirement takes a sand blast, a plain housewife clean up doesn't cut it.
An anodized heatsink just takes a wipe with a cloth now and then, ask yourself which one will perform better after some time.

Btw, heatsinks are made of aluminum alloy (6000 series for extrusion), not plain stuff, difference.
(me into boats, so i favor 5059 and 5383 )
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Last edited by jacco vermeulen; 21st February 2012 at 12:55 PM. Reason: fck, me make so many typos today
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Old 22nd February 2012, 01:14 AM   #1319
jerfer is offline jerfer  Canada
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Quote:
Originally Posted by jacco vermeulen View Post
Anodizing is basically just rapid corrosion of aluminum, making the oxidation layer multiple times thicker than the natural protection skin.
Thermal conductivity of the oxide film is much lower than blank aluminum, so clean aluminum with a fresh oxide tan will be a better heatsink.
Is this the reason behind sanding the anodized coating away before installing the FETs, to enable more and better heat transfer from the FET to the sink?

Quote:
Originally Posted by jacco vermeulen View Post
Anodizing does more than adding a fat oxide jumpsuit over the heatsink, the surface is dyed by filling the pores in the corrosion layer, then it's sealed.
The oxide layer of plain aluminum is not sealed, growth of the corrosion layer may be extremely small in a year's time, but the pores can hold on to particles.
...
An anodized heatsink just takes a wipe with a cloth now and then, ask yourself which one will perform better after some time.
So, in fact any color anodization will perform well at the temperatures we're dealing with here, it doesn't have to be black. The heatsink will stay cleaner and be easy to keep clean thus maintaining a high efficiency. Thanks, Jacco.

Jerry
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Old 25th February 2012, 10:01 PM   #1320
jerfer is offline jerfer  Canada
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Default Fan Blown Simulation

I took Jacco's advice regarding heatsinks and started simulating with fan-blown, high-fin-density, heatsinks. It's amazing how much dissipation you can get with this set up, even with low airflow values.

For simulating I used R-Tools from Mersen (formerly R-Theta) and it produced a whole report of the performance. One thing that struck me, though, is that despite the low heatsink temperatures at each Q (between 49 and 51 deg. C, using a SilPad 400 0.18), and the low temperature at the top of the sink (44 deg. C) the junction temperature it calculates is around 125 deg. C. I used an Rjc = 0.89 C/W value from the IRFP240 datasheet, and it assumes a 0.45 C in2/W value for the SilPad. I specified 30W of heat from each Q (total of 8, arranged like Peter's A-JX boards).

Should I be worried here? Is there something I may have missed or configured wrongly? I've attached the report if anyone wants to look at it.
Attached Files
File Type: pdf Rtheta Sim - Tunnel JX.pdf (144.3 KB, 53 views)
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