Dx Blame MKIII-Hx - Builder's thread

[MagicBox]

What a space, what an oppertunity to spread the transistors physically! I'd have tried to give eacch transistor much more Sq/Inch to give each a better buffer for thermal transients.

[AndrewT]

The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.

[AndrewT]

Originally Posted by MagicBox

What a space, what an opportunity to spread the transistors physically!.................a better buffer for thermal transients.

The PCB is done. It fixes the devices in a tight group.
Looks like it is designed for blown tunnel cooling. At the maximum power expected they are more like PA amplifier PCBs, where blown cooling is the norm.

[MagicBox]

Originally Posted by AndrewT

the PCB is done. It fixes the devices in a tight group.
Looks like it is designed for blown tunnel cooling. At the maximum power expected they are more like PA amplifier PCBs, where blown cooling is the norm.

Ah, with active cooling it's less of a concern yes I just didn't get that from the chosen heatsink - if it would have been these high-density fin designs I'd have assumed active cooling.

[AndrewT]

Your concern is valid.
The PCB is designed for tunnel cooling, if high power must be dissipated.
That tall heatsink is quite unsuited to obtaining good heat dissipation efficiency with the PCB.

[a.wayne]

^^^I guess you know this from your last 1kw/ch@1ohm build


Err, ahh i guess you mised the xtra outputs or the 7" tall caps ...... room for the soft start, regulated supply and the 8.5x4 " transformer ..

[meanman1964]

Originally Posted by AndrewT

The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.

Yes Andrew it is coated with a compound on both sides.I do use them very often.

[meanman1964]

Originally Posted by AndrewT

Your concern is valid.
The PCB is designed for tunnel cooling, if high power must be dissipated.
That tall heatsink is quite unsuited to obtaining good heat dissipation efficiency with the PCB.

I will use this sink

[Junie]

Originally Posted by AndrewT

The pic showing Kapton appears as pink. I thought Kapton was clear.
Is that isolator coated with some other material on one, or both sides?

Thin mica with Thermal compound on both sides is a very good heat conductor. Very few film based insulators can match it's Thermal performance. Choose carefully if you need good Thermal performance. Even fewer film based insulators can improve on thin mica+goop.
Kapton film on it's own is a flat surface that will not conform to the imperfections of the heatsink nor the device. Plain smooth Kapton requires Thermal compound on both faces just like mica.

Andrew it's not a Kapton it's a Sil-pads, here's what it says:

Sil-pads come in a few different varieties. The most common is a silicone rubber material reinforced with fiberglass. A different version has 2 thin silicone rubber layers sandwiching a layer of polyimide film. Many manufacturers use sil pads because they don't require grease to perform to spec (which makes assembly quicker and easier).

[a.wayne]

Originally Posted by meanman1964

I will use this sink

Nice setup for fans, fans will not work for me due to the noise, i will have a fan to cool the case if temps escalate , but only for those brief moments. Also i do not like the heat concentration such a setup creates ....

Originally Posted by Junie

Andrew it's not a Kapton it's a Sil-pads, here's what it says:

Sil-pads come in a few different varieties. The most common is a silicone rubber material reinforced with fiberglass. A different version has 2 thin silicone rubber layers sandwiching a layer of polyimide film. Many manufacturers use sil pads because they don't require grease to perform to spec (which makes assembly quicker and easier).

Thanks for that tid bit junie ....