😀
I read this thread in it's entirety several times back and forth. Trying to make shure no single bit of useful info slipped away...
As for heatsinks, barredboss on ebay has some good ones, he also now has a store:
HeatsinkUSA, llc
Thanks Jackies, reading this thread and all the links is paramount to an education in electronics. It's been 25 years for me so a lot of cobwebs getting cleared out😛
Tony
Tony
Looking for some suggestions. Finished my F5 build and it looked to come up without any issue and played music and the sound was pleasing. I used 1ohm resistors for r11/r12 and set the bias current to 900mA. The barred boss heatsinks were warm, but not anywhere close to being a concern. The setup is dual mono and the two 250VA transformers were extremely hot. Blistering hot. What would you check?
Stroob
Stroob
Hot transformers
Just a thought... no guarantees. If there is any DC offset (even a few millivolts) on your mains, you could be saturating the core of your toroidal transformer. There is a little circuit to prevent that DC from getting though:
2 diodes + 2 diodes (opposite polarity, in parallel) and a lot of capacitance across both (observing diode polarity). Essentially, the diodes prevent DC from getting into your transformer core and saturating it.
Hope that helps.
Ryan
Just a thought... no guarantees. If there is any DC offset (even a few millivolts) on your mains, you could be saturating the core of your toroidal transformer. There is a little circuit to prevent that DC from getting though:
2 diodes + 2 diodes (opposite polarity, in parallel) and a lot of capacitance across both (observing diode polarity). Essentially, the diodes prevent DC from getting into your transformer core and saturating it.
Hope that helps.
Ryan
I had some puny 180VA units and when running at stock bias, they would get very toasty to the touch.
Now on 440VA units (one/channel) and it's all cool as a cucumber.
Now on 440VA units (one/channel) and it's all cool as a cucumber.
@ Renron,
Ok sorry, I stand corrected. I only remember the first version of arctic silver and believe to remember that that version was/could be conductive. Maybe bad memory, maybe things have changed.
regards,
Joris
Ok sorry, I stand corrected. I only remember the first version of arctic silver and believe to remember that that version was/could be conductive. Maybe bad memory, maybe things have changed.
regards,
Joris
artic silver or not?
I have this silvery looking heatsink compound.
How can I test it to ensure it is either conductive or non-conductive during all operational conditions?
I have this silvery looking heatsink compound.
How can I test it to ensure it is either conductive or non-conductive during all operational conditions?
Ways and means.
Put a blob of the stuff on the plastic front of an old power transistor, then connect to PSU and use a pot on the base to vary bias (heat). Hold a scope probe or DVM to one side of the blob and connect hold a voltage source to the other and see what passes through.
If you want to be really sure and do detailed measurements, first epoxy a couple of wires to the transistor to make pads with which to bridge with the compound.
Were you snowed in ? 🙂
Put a blob of the stuff on the plastic front of an old power transistor, then connect to PSU and use a pot on the base to vary bias (heat). Hold a scope probe or DVM to one side of the blob and connect hold a voltage source to the other and see what passes through.
If you want to be really sure and do detailed measurements, first epoxy a couple of wires to the transistor to make pads with which to bridge with the compound.
Were you snowed in ? 🙂
Off Topic
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.
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.
@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.
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
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. 😀
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
Tony
Member
Joined 2002
@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 🙂
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 🙂
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
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.
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.