Hi dBel84 -
glad to hear that you have found the issue !
Hopefully that would mean that the 2SJ201 ist still functioning ?
I have had good success so far with classic mica & goop. What helps here as well is that the 2SJ201 / 2SK1530 come in slightly larger packages than TO-247 - it's TO-264 I think.
That gives more area to transfer the heat from the MOSFet to the heatsink; no issues here with 1.81 A bias current at approx. +/- 24V rail voltages.
Best regards,
Claas
glad to hear that you have found the issue !
Hopefully that would mean that the 2SJ201 ist still functioning ?
I have had good success so far with classic mica & goop. What helps here as well is that the 2SJ201 / 2SK1530 come in slightly larger packages than TO-247 - it's TO-264 I think.
That gives more area to transfer the heat from the MOSFet to the heatsink; no issues here with 1.81 A bias current at approx. +/- 24V rail voltages.
Best regards,
Claas
I give the backside of high power semiconductors a couple of very light swipes across a flat diamond whetstone, before mounting them. It reassures me that I did everything possible to get rid of burrs and spikes on the mounting surface, which might damage the insulator pad.
Here is an example (link)
Here is an example (link)
if anything, the Keratherm appear to be thinner and more prone to puncture?
I dont know, they are awful thin.
Russellc
Thanks for the kind words all, still feel stoopid but at least I know what is going on. It would never have occurred to me as the other channel has not faltered since the initial set up and all the fets have the same isolation pads.
did a little "dumpster diving" and rescued the toshiba fets that had been thrown out - still missing one 2SJ201 but now I have a full set at least with a few more 2SK1503's to spare.
- I will set up a test rig at some point to make sure they are still functional.
thanks - Ordered the whetstone - never tried this before.
..dB
did a little "dumpster diving" and rescued the toshiba fets that had been thrown out - still missing one 2SJ201 but now I have a full set at least with a few more 2SK1503's to spare.
- I will set up a test rig at some point to make sure they are still functional.
thanks - Ordered the whetstone - never tried this before.
..dB
Aluminum oxide ceramic insulator pads are about 2x more thermally conductive than keratherm (when used with heatsink compound) and are about 1mm thick and tough and do not short.
I use them on the Alpha BB amp where about 100w of dissipation per MOSFET needs to be conducted to the heatpipe CPU cooler block. MOSFET body temp is about 38C so works very well.
I have had silicone spacers short out with pin holes before. A good check before applying power is to check continuity meter from heatsink ground to drain (tab). Burr around tapped hole are common.
4180G Aavid | Mouser
10pcs TO-247 1mm Aluminum Oxide Alumina Ceramic Insulator plate High Temperature | eBay
I use them on the Alpha BB amp where about 100w of dissipation per MOSFET needs to be conducted to the heatpipe CPU cooler block. MOSFET body temp is about 38C so works very well.
I have had silicone spacers short out with pin holes before. A good check before applying power is to check continuity meter from heatsink ground to drain (tab). Burr around tapped hole are common.
4180G Aavid | Mouser
10pcs TO-247 1mm Aluminum Oxide Alumina Ceramic Insulator plate High Temperature | eBay
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This is why you finger twirl a countersink bit into every just-tapped hole. You can buff too, using one of your wife's fingernail thingies. Or using emery cloth and a light touch. Or a dremel motortool with buffing pad and very light touch. Or a Q-Tip dipped in Mothers Mag & Aluminum Polish, from the auto parts store.
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I always deburr aluminum heatsinks now once it has happened. But one time I was mounting a mosfet for a cap Mx onto the bottom steel chassis panel and sheet metal screw is not what to use as it causes metal to swell up and pierce the insulator. Now I drill holes and use nuts and bolts after deburring. Luckily it was a simple short of the drain to GND and that blew a fuse and everything was fine once problem identified.
There is also AlN (Aluminum Nitride) nontoxic ceramic insulator which is much more effective than Aluminun Oxide in thermal conductivity.
It was recommended by very respected man in russian diy community for use in class A amps which is how I discover it. Didn't tried it myself yet.
You can see comparison sheet here: http://c-component.ru/sites/default/files/attach/teploprovodyashchie_prokladki.pdf
I am sorry that it is in cyrillic but sheet comparisons mostly understandable (second page).
First on comparison the list goes mica, then Nomacon KPTD insulator (local brand and model), Beryllium Oxide (toxic ceramic), Aluminun Oxide and then Aluminum Nitride.
I hope this information will be useful.
Yep. I use a small bit designed to counter sink screws with cone shaped head. Removes all burrs.
Russellc
looks like everyone got distracted by burrs and heatsink pads
these numbers are perfect ..dB
looks like everyone got distracted by burrs and heatsink pads
Speak for yourself, I was distracted by RainfallSky's avatar!
Speak for yourself, I was distracted by RainfallSky's avatar!
No burrs there.
I only know of one small company in Moscow, they make them by custom orders.
Unfortunately, they do not sell outside the country.
Now that I tried to search for international sellers, the only one I could find is Aliexpress..
As always with chinese sellers there is no 100% way to tell what kind of ceramic they will send.
Speak for yourself, I was distracted by RainfallSky's avatar!
I thought to myself once, I hope it will not be too distracting..
