Thermalright CB-6L

SUMMARY: Thermalright’s CB-6L copper/aluminum hybrid does quite well with a Delta 38 for Socket A cooling.


Measures 64mm wide x 77mm long x 32mm high (no fan).

Thermalright is introducing a new product that is engineered along more conventional lines than its copper SK6: the CB-6L. They sent one to us for testing. It features a copper base that appears to be soldered onto its aluminum fins. It arrived powered by an anemic 60x15mm fan that is very quiet but lacks the “oomph” to make this a serious contender among performance heatsinks – like its own SK6 with a Delta 38.

I’m sure that Thermalright is marketing the CB-6L as an OEM or lower cost unit to round out their product line. As such, it looks like a unit worthy of consideration, but performance is highly dependent upon the fan used.

The clip is what I call the “OEM Clip” – it requires a screwdriver to mount and dismount – as does the SK6. It is quite secure, but not very user friendly.


The base is a copper plate that extends the length of the heatsink (77mm – this is not designed for Socket 370 use, although I was able to mount it on Iwill’s BD133). It is not finely polished but it’s free from noticeable machining marks. Where the Thermalright may have an edge is on the bond between the aluminum base and copper plate:


As this pic shows, this is not a mechanical bond (e.g, using screws) that I have seen on many other hybrids; rather, it appears that it is soldered – a very tricky process. What this does, however, is to markedly increase the heat transfer between the copper-aluminum surfaces; a mechanical bond usually relies on pressure and thermal grease. The other alternative is the Alpha approach – a “shrink fit” – which, done correctly, is very efficient.


I prepared the Thermalright by boring a hole completely through the base so I could epoxy a thermocouple above the CPU. The thermocouple is attached to an Omega HH23 Digital Thermometer. Ambient temps were measured with a thermocouple placed about 1 inch from the fan’s intake. I used Prime 95 to stress the CPU on an Iwill BD133 (MBM temps are on-die) and ABIT KT7. Arctic Silver grease was used in all tests. CPU Case Temp is the temp at that point where the CPU contacts the heatsink, CPU Back Temps are measured by a thermocouple on the center back of the CPU.

I tested it with three fans: the anemic stock fan (about 22 cfm), the 26 cfm YS Tech and the Delta 38. Fan noise was measured with a Radio Shack Sound Meter placed 8″ from the fan’s intake; I recorded 70 dBA for the Delta 38, 60 dBA for the YS Tech and 56 dBA for the stock fan – very quiet.


CPU Case Temp

Ambient Temp



MBM Temp

CPU Back Temp

T-Bird @ 1133/ABIT KT7/Delta 38 (68 watts)

43.6 C

27.8 C



42 C

46.9 C

T-Bird @ 1300/ABIT KT7/Delta 38 (83 watts)

47.2 C

28.0 C



46 C

51.1 C

Duron @ 1000/ABIT KT7/Delta 38 (63 watts)

44.4 C

27.9 C



45 C

51.2 C

Duron @ 1000/ABIT KT7/YS Tech (63 watts)

49.8 C

28.9 C



50 C

56.5 C

PIII @ 933/Iwill BD133/Stock fan (26 watts)

37.1 C

27.1 C



44 C


PIII @ 933/Iwill BD133/YS Tech (26 watts)

36.7 C

27.5 C



43 C


PIII @ 933/Iwill BD133/Delta 38 (26 watts)

35.0 C

27.3 C



42 C


Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt the CPU radiates, the heatsink will cool the core by the (C/W x watts) plus ambient temp. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Socket A results place the Thermalright towards the mid to lower end of C/Ws for “acceptable” (C/W < 0.30) Socket A heatsink cooling with the Delta 38. I tested the Duron with the YS Tech to see how it would fare, and it bumped it out of the acceptable range. The heatsink became quite warm to the touch; this indicates that, with the YS Tech in high wattage conditions, the CB-6L is starting to saturate (like “hitting the wall”). The stock fan is a non-starter, as is the YS Tech with a high wattage T-Bird.

PIII cooling is most likely not an option on most motherboards, as it may not clear capacitors around the socket. Performance is OK on PIIIs but nothing to get excited about.


Thermalright’s CB-6L is a competitive Socket A cooling solution among “performance” heatsinks, although many will find the Delta 38 annoying and untenable. The YS Tech could be a option for OK cooling, but not recommended for power users. The stock fan is not a serious option. depending on price, the CB-6L could be a good price/performance buy.

Many thanks to the good folks at Thermalright for sending the CB-6L our way.

Email Joe

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