Reliability of heat pipe as heatsink

[Jacky]

Hi!

Back in the early 90's or so I remember seeing a kind of heatsink
which was called heat pipe and used primarily in Japanese made
amplifiers and receivers.
It is a 8" or 9" copper pipe about 3/4" in diameter closed at both ends.
A number of aluminium fins (each fin is about 4"x4") are fitted on the
tube
(much like the heating element in a electrical baseboard heater),
except at one end where a aluminium block can be clampped onto it
with the power transisters mounted on the block.
The tube has some kind of fluid inside that helps
conducting the heat through the copper heat pipe and it makes a hiss
sound.

The reason I am asking is that I just got a power amp kit which was
made
in the 90s that uses this heat pipe.
The amp can be set up to run at 100W class AB per channel or 25W
class A at a reduced supply voltage.
For the 25W class A mode of operation it is suppose to be biased very
heavily.
I am just not sure if this funny heatpipe can really dissipate all that
heat reliably and whether this heat pipe may fail after some time.
If I know that it is not a reliable heatsink then I may consider not to
bias it
heavily and also not to drive it at high power.
(It may not even worth my time to assemble it.)

Anybody remember this type of heatpipes and if they are reliable ?

Thanks in advance.

Cheers,
Jacky

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[James Sweet]

I've never seen one in an amp, but I have in laptop computers and I've
never heard of one failing. Why don't you install a thermal cutout
switch on the block that the transistors are mounted to?

[Steckrich]

Yes, I have serviced some old Technics models employing this design. They seem
quite reliable UNTIL the fluid in them ages. Most of the units I saw were 8
years or more old when they came through for service, but the replacement tubes
were not available. The fluid either drys up or, I believe, bakes into a more
viscuous or even solid substance that no longer does it's job. Happy holidays!
SteveE