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Old 16th February 2013, 01:39 PM   #1621
bcmbob is offline bcmbob  United States
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jacco,

I'll have to look back through my search history cause I did see a 1 mil 12" X 12" sheet somewhere - not mica but a Kapton/alternative product.

However, you did point out something I have been considering and planned to ask about at some point. I don't know if a careful butt joint of something like one of the following two products would jeopardize the dielectric seal at the joint. That would not be a problem between faces like the earlier picture points to, as no electricity exists at that level. But generally, I'm curious if anyone has made (or even considered) a successful insulator splice for a power transistor.

Also, as a discrete nubee, does anyone make an insulated PT (as available with LM3886 chips) where only heat transfer compound is needed?

1 Mil Kapton Tape - 3in, Polyimide Tape Online

Kapton Film (HN Series) - 2in, Polyimide Tape Online
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Old 16th February 2013, 03:39 PM   #1622
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Depends on the insulator thickness, no ?

Diamonds are a fool's best friend : Krell KSA 50 pcb

(worst case, one could glue the gap shut, i'd think)
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Last edited by jacco vermeulen; 16th February 2013 at 03:43 PM.
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Old 16th February 2013, 04:09 PM   #1623
bcmbob is offline bcmbob  United States
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Well, Well!

I actually have 12 of the Thermalloy pads for my discrete amp, but I haven't used them as I thought I'd screwed up my online order. Was also under the impression the thickness would inhibit heat transfer. Are those in the link clean or did you add a compound?
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Old 16th February 2013, 04:41 PM   #1624
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They require goop.

As shown in Patrick's article, thermal conductivity of Aluminum Oxyde is really good, but the insulator thickness seriously drops that advantage.

Back in the mid '80s I bought 4.5mm AlOx insulators, pretty useless compared to mica.
Advantage then was that they could be used over and over again, big plus if one hasn't finished a project and already coming up with the next. (as neat as braided hose with fast connectors, to someone into boats and cars)

In time, they became thinner, the Aavid ThermAlloys of the Krell thread do better than mica, also better than e.g. trendy Bergquist ceramics filled sheet items at the time.
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Old 16th February 2013, 10:26 PM   #1625
WalterW is offline WalterW  Netherlands
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Quote:
Originally Posted by omishra View Post
They are passing 10sec hand touch test with 0.6A/device bias. That was maximum possible for these heatsinks. But here now daytime temperature is 30deg Celcius. It will touch 40-45 during next couple of months. So keeping in mind that rise, I reduced bias to 0.55A/device.


Speaker grounds are taken from amp PCB. From PS ground(floating), wires go to earth ground isolator and amp board.
Ah, I get it... your T-ambient is a bit different than in the Netherlands
Here it's about +5 deg Celsius outside, and in my room 18 deg Celsius, hahaha

Maybe I have to reconsider to take my speaker grounds from the amp-board, instead of my PSU-board...
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Old 20th February 2013, 02:00 PM   #1626
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Here are some photos of my finished F5 turbo monos.
Each Mosfet is biased to 0.8A.
The bases are 59°C, the heatsinks are 57°C.
The room temperature is 25°C.
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Old 20th February 2013, 02:03 PM   #1627
biju55 is offline biju55  India
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Great Looking Amp ................
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Old 20th February 2013, 02:39 PM   #1628
coils is offline coils  United States
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Originally Posted by rookakoma View Post
Here are some photos of my finished F5 turbo monos.
Nice work, love your design!
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Old 20th February 2013, 02:46 PM   #1629
coils is offline coils  United States
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Here is a pic of my F5c with parallel source diodes. Im doing a preliminary bias now, its at .85 amps per device. Im trying to dial in on where the diodes begin conducting. It has .47 ohm source Rs, and 100 ohm parallel feedback Rs.

I dont think I can bias this much higher on my horizontal heatsinks.

The psu is all C right now, im waiting for choke coils.
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Old 20th February 2013, 03:36 PM   #1630
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Turn your sinks the other way. It has a great effect on dissipation. I wouldn't go much higher than .450 across Rs and that's assuming easy load.
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