F5 power amplifier

[AndrewT]

Originally Posted by Mooly

Were you snowed in ?

initially snowed out but climbed the hill through 2 & 3foot drifts.
Then snowed in and clambered down the hill through upto 4feet drifts to find my abandoned car under 18inches of snow.
Took 45mins to dig it out with the help of a couple of villagers and drove into Edinburgh where I stayed until the electricity was restored 36hours later.

[jackinnj]

Originally Posted by Renron

PS, Please disregard my messy desk

Are you using the compass to determine it's magnetic properties?

[sangram]

@Andrew - I would use appropriate safety precautions, stick a high voltage source (B+ source from a tube amplifier power transformer or following rectifier) into the middle of a blob of compound and check conductivity all around the blob, using a hot air gun to elevate the temperature, and a spot freezer to lower it.

[Renron]

Originally Posted by AndrewT

initially snowed out but climbed the hill through 2 & 3foot drifts.
Then snowed in and clambered down the hill through upto 4feet drifts to find my abandoned car under 18inches of snow.
Took 45mins to dig it out with the help of a couple of villagers and drove into Edinburgh where I stayed until the electricity was restored 36hours later.

LOL,
Sounds like a normal winter at Lake Tahoe.
Glad you made it out and defrosted yourself.

Jackinnj,
I used the compass to test for any magnetism in the compound, found none. However a bic pen did move the compass needle slightly. Surprised me.
I used a Fluke DMM (shown) to test for continuity, none.
Years of servicing other people's computers I have seen the pin cavity of CPUs filled with arctic silver by some well intentioned customers, they DID get hot as CPUs do, and they were still worked without shorting. (Dumb Luck? dunno) Their issues were mostly due to software operator error.

Ron

[Renron]

Originally Posted by sangram

@Andrew - I would use appropriate safety precautions, stick a high voltage source (B+ source from a tube amplifier power transformer or following rectifier) into the middle of a blob of compound and check conductivity all around the blob, using a hot air gun to elevate the temperature, and a spot freezer to lower it.

Sangram,
How is it relevant to use ~300V from B+ to determine Arctic Silvers appropriate usage as a thermal compound on a 24V rail? We are still using an appropriate insulator are we not?
Sort of like testing a 120V breaker with 240V AC.

Sorry, I just don't get it's relevancy.

Ron

I have no emotional or financial interest in Arctic Silver or it's subsidiaries.

[wingman65]

Arctic Silver is NOT recommended for use on mosfets as it CAN be conductive. There are non silver based thermal grease types for these applications. Best not to take the chance.



Tony

[jleaman]

Originally Posted by wingman65

Arctic Silver is NOT recommended for use on mosfets as it CAN be conductive. There are non silver based thermal grease types for these applications. Best not to take the chance.



Tony

Agreed.!

[sangram]

@Renron: It said *all* operating conditions, not just those for the F5 Since most solid state devices are specified to 150V, one would probably be well-served to check failure mode at twice the rated votage.

And one operating condition could be the presence of mains voltage or close enough in the case of defective mains wiring (which in my country is 230V). I guess if you had 230V AC on the chassis and the output of a rectifier coming together through the compound and the metal tab - well...

It's not likely, but failure mode testing is failure mode testing. Obviously it is not expected under operating conditions, but the question was not about operating conditions

[Renron]

Originally Posted by wingman65

Arctic Silver is NOT recommended for use on mosfets as it CAN be conductive. There are non silver based thermal grease types for these applications. Best not to take the chance.

Tony

OK, I'll bite. Where does your information come from? Both that it's not recommended for mosfets, and it can be conductive?

Remember this stuff was designed for CPUs, and we all know how hot they get! Much hotter than your hair dryer.

Playing the devil's advocate here. Not trying to start any kind of fight. I just want to know where this information is coming from, when the manufacturer says that it's not conductive. Would sure make them liable if it was conductive.

Again, not wanting to pee anyone off, but please state your source of information.


Sangram,
If you've got 230V to the mosfets.................you've got bigger problems than the type of thermal paste. LOL. I do understand your point though.

Straight rip from A/S website:

"Not Electrically Conductive:
Arctic Silver 5 was formulated to conduct heat, not electricity.
(While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.)

Absolute Stability:
Arctic Silver 5 will not separate, run, migrate, or bleed."

Ron

[nigelwright7557]

Even if it was conductive or slightly conductive it depends how mad you go with it.

I was taught that you only put on a very thin layer.
In tha tcase the top layer shouldnt touch the bottom layer.

Most insulators are bigger than the transistor anyway.