Review: Thermalright ALX-800 AlCu hybrid cooler


January 23, 2004 by Russ Kinder

ALX-800 cu/al heatsink

To put it simply, Thermalright has been the 400lb gorilla of the heatsink market over the past year or two. As processor wattage spiraled upwards, Thermalright produced ever more powerful heatsinks to keep them at the top of the performance heap. The downside to this heatsink arms race is that each generation has been bigger, heavier, and more expensive than the previous.

While every enthusiast might like to own the highest performance cooler, the realities of the market are that not everyone is willing to pay the big dollars for that kind of performance. There will always be more mid-level "value" buyers than there are "bleeding edge" buyers. It's with these "value" consumers in mind that Thermalright seems to have designed their new ALX-800 heatsink. On the other hand, perhaps it's the need to have at least one heatsink in their lineup that falls within AMD socket-A heatsink weight recommendations.


Tharmalright isn't charting any new design territory here. The ALX-800 is based on the SLK-800, only constructed from aluminum with a copper base instead of the all copper common to the rest of the Thermalright line. In fact the ALX-800 is Thermalright's first AlCu hybrid cooler since the venerable AX7.

Regardless of material, there's no denying the ALX's heritage.


Top, without fan (mm)
L84 x W58 x H42
L87 x W56.4 x H48
Base (mm)
L32 x W58
L25 x W56.4

The ALX-800 is constructed of a tapered copper core with a bank of aluminum fins attached to either side. Unlike the SLK, where each of the fins is soldered individually to the base, the fins on the ALX are machined from a single chunk of aluminum. The advantage of this method is that there are fewer solder joints to assemble, which reduces manufacturing costs. Having all the fins as part of one continuous mass also increases the ability to transfer heat from the hot fins in the center to the cooler fins at the ends, improving efficiency. The downside is that machining the fins this way forces you to use much thicker fins.

When you pack the same number of thicker fins into the same area as you did with thin fins, the net result is a loss of airspace. Compared to the SLK, the ALX has less than half the space in between the fins.

This does not bode well for low-airflow performance. The lower the airflow, the more important the fin spacing becomes. With a high-flow fan, the air can be pushed deep into narrow slots, but with lower CFM there is less force available to shove the air down between the fins. As the airflow drops, this effect becomes more significant.

The copper base of the ALX is similar in concept to the SLK's; it serves as a broad conductive path for the heat from the base up to the fins' midpoint, rather that just transferring the heat to the fins at their base. Unlike the SLK, the ALX's base is open at the center, which should allow more direct airflow down to the innermost areas of the heatsink.


The base on the ALX isn't as smooth as it was on my original SLK-800, and its nowhere near the OCD polish of a Swiftechs, but it's not bad either. Some fine machining marks are just barely visible, they can be felt with a fingernail.

Some things never change: The clip is the classic Thermalright 6-lug spring clip. If its not broken.... It provides excellent rigidity of mounting, and ensures compatibility with any socket A socket. (It also works on Socket 7 boards.)

The fan mounting mechanism is another area that shows an evolutionary change from the SLK. While still using the wire mounts, they now attach to the bottom flange of the fan, instead of the top. This simplifies installation, since now only 1 set of holes are needed in the heatsink body, regardless on the fan thickness. It also allows the use of ThermalRight's duct mod under the fan.


Test Bed for ALX-800

* Abit NF7 motherboard, with latest BIOS revisions. Modified with passively cooled NB.
* AMD XP2100 Thoroughbred B, at stock speed and voltage (1.65v, 62.1 Watts max)
* 1GB of PC2100 RAM.
* ATI 9500 graphics card, cooled with Arctic Cooling Silencer VGA cooler.
* Seagate Barracuda IV hard drive.
* Enermax 365 PSU, modded with a Panaflo 80L1A fan @7 volts.
* Temperatures are read with Motherboard Monitor 5.
* CPUBurn was run for 15~20 minutes to achieve load temperatures.
* Ambient temperature during testing was 20°C.


In accordance with standard SPCR heatsink testing methodology, the reference standard 80mm Panaflo L1A low speed fan was used for all the tests. Each test was conducted a minimum of three times, and the average reading is shown. For comparison, previously recorded results for the SLK-800 are also included.

°C rise
Panaflo @ 12V
Panaflo @ 7V
Panaflo @ 5V
°C rise refers to the rise in temperature over the ambient at load.


°C rise
Panaflo @ 12V
Panaflo @ 7V
Panaflo @ 5V
Temps adjusted -2° to account for difference in ambient temp.

Surprised? So was I. So much so that I re-ran the entire test sequence all over again, but the results were the same. The load temperature with the Panaflo at 5V reached 81°C before the test was halted. No point burning a CPU. It's true that at 5V, the Panaflo 80L1A pushes so little air that even the best cooler don't give great results. But still, at this low airflow the ALX-800 sets new record high temperatures. But if you think about it, the results are not surprising at all:

In comparison to the SLK-800, the ALX:

* Has nearly the same surface area. (thickness of the fins adds only tiny amounts of useful surface area)
* Has fins with 60% lower thermal conductivity
* Has half the airspace between fins, causing higher airflow impedance

At higher airflow rates the ALX performs fairly close close to the SLK, as would be expected. The Panaflo 80L's 24 CFM at 12V is enough to overcome the above handicaps that are so crippling at lower airflow rates.


It looks nice, is well-made, priced well enough, and performs fine with a Panaflo 80L fan at 12V. With a higher airflow fan, it can probably perform several degrees better -- at the expense of more noise. This is probably good enough for the bulk of the middle "value" market Thermalright may be targeting.

For PC silencers, the noise level of a Panaflo 80L fan at 12V is generally not quiet enough. Its performance in our testing with the Panaflo fan at 7V is already marginal, given the 20°C ambient. Inside a case where the minimum temperature is at least 10°C higher, we'd be looking at a CPU temperature of 72°C, which is likely unacceptable for most PC enthusiasts. We really can't recommend this model for quiet enthusiasts.

Our thanks to online retailer for giving us the opportunity to examine the ALX-800.

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