Power amplifier heatsinks

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g8vpg
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Joined: Fri Oct 11, 2013 9:35 am

Power amplifier heatsinks

Post by g8vpg » Sat May 04, 2019 1:53 pm

Does anybody know about the grey coloured, plastic looking film that is often applied to heatsinks? I am led to believe that it is a heat conducting layer that is used in preference to conventional heat sink paste. My QO100 amplifier heatsink has this film applied, but it is clear that the amplifier case is quite a bit warmer than the heatsink and it looks more like an insulating layer to me. Does anyone have any professional knowledge of why and how this is used?
73 Shaun.

g0mjw
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Joined: Sat Sep 20, 2014 9:15 am

Re: Power amplifier heatsinks

Post by g0mjw » Sat May 04, 2019 2:16 pm

Sounds like a thermal pad. It will have some thermal resistance so you expect a gradient across it.

E.g. https://uk.farnell.com/3m/120mm-1m-0-5m ... dp/2820143 where you will find a data sheet.

Mike

G8GKQ
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Re: Power amplifier heatsinks

Post by G8GKQ » Sun May 05, 2019 3:16 pm

Hi Shaun

Those thermal pads were standard on the GigaTech PAs and blown heatsinks. Mine was in a bit of a state so I scraped it off and used heatsink compound.

The "Polish PAs" that Noel and I now use also have one. Seems quite effective when properly mounted (>200 W dissapation on mine)

Dave

G1BVI
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Joined: Wed Aug 02, 2017 7:32 am

Re: Power amplifier heatsinks

Post by G1BVI » Sun May 05, 2019 7:09 pm

Be careful because it could be an insulator too.
Not seen an image but back in the day 2N3055 devices in a TO3 package had to be insulayed from the heatsink but still im thermal contact using thermal paste
Mica washers were used and other materials.

73

Nick

Trident
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Joined: Thu Mar 08, 2018 10:28 pm

Re: Power amplifier heatsinks

Post by Trident » Sat Sep 28, 2019 9:22 pm

Hi,

From my understanding, anything put between a device and heatsink will increase the thermal path resistance, so unless it is taken into account during the design stage nothing should be added later. I also believe thermal paste when applied should only be a very thin film, as it's designed to fill tiny voids in the mating surfaces to provide perfectly flat contact faces thereby improving heat transfer. Of course as previously mentioned, thermal pads may also provide an electrical insulation as needed, but will introduce extra thermal resistance.

GalmOne
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Joined: Fri Oct 18, 2019 4:07 pm

Re: Power amplifier heatsinks

Post by GalmOne » Wed Oct 23, 2019 3:03 pm

Speaking of heatsinks, are they appropriate for all climates or should they be reinforced for warmer places? Because I live in Belgium that has a similar climate as the UK, but I was considering these houses in Greece for the holidays as well, and the temperatures there are not exactly the same as on the coasts of the Channel.

g0mjw
Posts: 933
Joined: Sat Sep 20, 2014 9:15 am

Re: Power amplifier heatsinks

Post by g0mjw » Wed Oct 23, 2019 5:12 pm

Yes and no. 20C is not such a huge difference and in any case when holidaying in the Mediterranean you should be spending time of the beach or outdoors appreciating that large yellow thing rarely seen in Belgium or the UK and the local culture - not on the satellite.

Mike

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