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R-Theta Group Buy Anyone?

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The company for which I head up the procurement team is a Customer of R-Theta. Using my new influence, I have some special pricing, the likes of which I do not beleive were available to our community before now.

This particular profile has been around the block here at about $55 US plus taxes and shipping for very large Qty buys a few years ago before metals started climbing in price.


How about $47.50 CAD plus taxes and shipping for Clear Anodized 11" sections if I buy 50 pecies?

A) Quote is based on providing R-Theta extrusion 65340 cut to 11.0+/- 0.020'' length.
B) Quote is based on clear anodize finish per MIL-A-8625, TYPE II, CLASS 1, CLEAR.

Regards

Anthony
 

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Ed LaFontaine said:


....so using the thermal resistance given for a 3" section of 0.6, the thermal resistance of an 11" section would be...0.163?



Unfortunately, no. The relationship is not linear because the heatsink depends on "room temperature" air to meet those specs. By the time the air conducts heat away from the lower portion of the heatsink and rises to the upper portion, it's warmer than room temperature and the efficiency of the heat transfer decreases rather quickly.
Heatsinks much taller than 6 or 8" may look nifty, but they really aren't all that much better at getting rid of heat than something 6-8" or shorter. If your goal is how it looks, go for it. If it's heat transfer, you'll waste money.
There's an easy-to-use calculator at Aavid-Thermalloy that can give you a gut feeling for these things even if the heatsink isn't exactly the same profile. Since a lot of the heatsink manufacturers have pretty similar profiles you can probably find something close to the one Coulomb is offering.

Grey
 
Hmmm, the thumbnails disappear when you hit reply. I think I can do this from memory without having to open a bunch of windows or print the images.
Note that the 8" section is more consistent in temperature when comparing top to bottom. The taller section shows a distinct difference between top and bottom rows. Not only are the top devices running hotter than the bottom ones, but you'll find that the top and bottom rows won't bias quite the same due to the temperature differences.
Is it the end of life as we know it? Of course not. And it's nothing specific to R-Theta--just simple thermodynamics that applies to every manufacturer of heatsinks.
A twice-as-tall heatsink will dissipate somewhat more heat than a shorter one, but not twice as much. If you compare a 12" section to two 6" sections of the exact same profile, you'll find that two shorter sections beat one taller one every time, even though the surface area is the same, the profile is the same, the ambient temperature is the same, same number of active devices dissipating the same number of watts of heat, etc. I don't think of it as degrees C/inches of heatsink. I think of it as Pd/$. The math works out a little differently that way.

Grey
 
Coulomb said:
The company for which I head up the procurement team is a Customer of R-Theta. Using my new influence, I have some special pricing, the likes of which I do not beleive were available to our community before now.

This particular profile has been around the block here at about $55 US plus taxes and shipping for very large Qty buys a few years ago before metals started climbing in price.


How about $47.50 CAD plus taxes and shipping for Clear Anodized 11" sections if I buy 50 pecies?

A) Quote is based on providing R-Theta extrusion 65340 cut to 11.0+/- 0.020'' length.
B) Quote is based on clear anodize finish per MIL-A-8625, TYPE II, CLASS 1, CLEAR.

Regards

Anthony

This was actually the exact profile I was thinking of switching to instead of going with Conrad. They quoted me at pretty much the same rate ($46USD) for 12" sections, which at first was significantly cheaper than Conrad. The problem was that they charge a ridiculous amount for milling, drilling, and/or tapping. The Conrad heat sinks are also already finished in black enamel, which provides a better thermal rating. All in all, looks like a good heat sink though.
 
Okay Grey so two 6" sections will work better than one 12" section with what I imagine is a bucket load of caveats.

So if you require enough Heatsink to dissipate 250Watts for an Aelph 2 class amp you would still need 4 x 6" of this profile per channel. The amp is still going to look "Nifty" with all that Heatsink material, now you just got to be creative in how you configure it.

Personally I think the trade off in Thermal effeciency of a continuos Heat Sink as opposed to one with a thermal break is out wieghed by practical design considerations.

I do agree if you don't mind an Amplifier that is 22" to 24" deep two smaller heatsinks end to end would be more effecient.

Anyway I did not come back after a two year hiatis to start an argument, if I wanted an argument I would have tried the other door. ;)

Anthony
 
Re: Re: R-Theta Group Buy Anyone?

cwujek said:


This was actually the exact profile I was thinking of switching to instead of going with Conrad. They quoted me at pretty much the same rate ($46USD) for 12" sections, which at first was significantly cheaper than Conrad. The problem was that they charge a ridiculous amount for milling, drilling, and/or tapping. The Conrad heat sinks are also already finished in black enamel, which provides a better thermal rating. All in all, looks like a good heat sink though.

Black is available as well, and they are still expensive for custom mill work. More than likely I will just get what I need as these Group Buys do not work well for goods that cost more to ship than they do to buy.

Anthony
 
And as I am not about a closed mind, but rather open if not somewhat annoying conflicting opinions. Here is a Thermal Plot that demonstrates Grey's argument that you could achieve better results with two 6" sections rather that one 12", design choices aside.

3 x 30Watt on 6" of 9012.

There is not a huge difference in average temperature if compared to the very first plot, but there is a consistent 3 Deg lower temperature on the latter.

Anthony
 

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Trust me...I don't like it either. I just file it under "life just ain't fair sometimes" and try to figure out how to get rid of all that confounded heat. I've even seen Big Name Companies bring out products that showed they hadn't quite thought the heat thing through. Or someone thought it looked neat and managed to overrule the fellow who actually designed the circuit.
If you can make the math work out, feel free to use taller heatsinks. If, as I tend to find, you're weighing dollars against degrees, you have a couple of other options:
--Run shorter lengths around the entire perimeter the way Nelson did with the Alephs
--If you're intent on doing rack stuff, or at least something with a front that doesn't look like a porcupine, you can still try to run heatsink along the back
--You can double up by running more heatsinks inside the chassis--obviously this will require venting though the top and, yes, the inside heatsink will run hotter than the outside ones--consider running fewer devices on the inside heatsinks in an effort to balance the temperature
--I'm not a big believer in using heatsinks on the top or bottom of a chassis because there's no convection, but if you're desperate you can get rid of some more heat that way--it's even less cost effective than tall heatsinks, though
--You might consider using a thermostat to switch on fan(s) if the heatsink exceeds some predetermined temperature--the assumption being that the music is loud and the fans will be less annoying--this assumption does not hold true for class A amps
--If you're against the wall and all else has failed, turn on the fans--fans are a lot quieter than they used to be and you can get a surprising amount of airflow even running them at half-speed
I wish this was more open to interpretation, but it's not a sonic "I think this sounds better" sort of thing...it's an "Ohmigawd my amp just flamed out" sort of thing. Better to have too much heatsink than too little. Amps don't die from being too room temperature, they die from being too hot.
Remember not to stack amps that will run hot. If they're in a rack, space them apart by at least the same height as the heatsinks. That's just a rule of thumb, but it works fairly well.
Take it from a guy who runs a lot of class A amps...

Grey

P.S.: Interesting factoid--class A amps run cooler when playing music because the wattage that would have been dissipated through the heatsinks is dissipated in the speaker instead. Do not count on this effect to keep your amp from self-destructing.
 
Geoff (a member here--yes, the same guy who has the Class A website) once found a site where they compared heatsinks with various coatings: paint of various colors, anodizing, naked aluminum, and about seventy-'leven other things. Naturally, I assumed black anodizing would be the clear winner. Not so, according to those guys. If I recall correctly, green paint was the best. Ugh. Gimme the black anodizing, anyway. The idea of green paint for heatsinks just churns my stomach. Sorry, can't do it.
I have no earthly idea how to find Geoff's post. It was years ago. If you want to try to unearth the link, you might ask Geoff. Perhaps he will remember.

Grey

EDIT: Huh! Imagine that...I got lucky and found Geoff's post on my third try. Unfortunately, that used up all my luck for the day. The link is broken--gets a 404 error. Bummer. Just go with black anodizing and save the green paint for your bedroom or something.
 
The KL-271 heatsink profile is the best natural convection design I have found, and could be used as a performance reference for this purchase. It is anodized black. It was discussed in the Leach website and wiki diyAudio.com recent group purchase.
The R-Theta 9012 profile shown above looks similar to the KL-271.


http://www.diyaudio.com/forums/showthread.php?threadid=56086&highlight=
 

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You could check what the Seifert sinks currently will cost you.

Looking at the thermal plots Anthony posted, the CAD 47.5 for an 11" extrusion is a good deal.
Personally i'm not that impressed by the Conrad sinks, low grade performance for a low dollar bill, nice if you don't mind the additional inches.

The monaural Aleph-J's i'm assembling run on 2-1/5" high heatsinks.
Even have to lower the transformer donut by a fifth inch beneath the chassis to fit inside the shallow case. (does have the plus-side of a damped and vented sub-chassis for the toroid )
The caveat lector is a chassis length of 16". Aargh, the choices in life are so difficult, it's killing me.
 
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