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Transistor insulator pads
Transistor insulator pads
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Old 26th May 2019, 08:25 AM   #1
Mark 461 is offline Mark 461
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Question Transistor insulator pads

Good Morning all,


I'm looking for insulator pads for my amplifier. Long story short was checking for an issue with it and ended up creating one lol. I took off these plastic looking sheets off the bottom set of transistors, and now the amp consistently blows its 10 amp fuse. Can I find this part or at least a good alternative in a hardware or building supplies store? This is for a denon receiver btw. Thanks.
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Old 26th May 2019, 09:28 AM   #2
Mooly is offline Mooly  United Kingdom
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Transistor insulator pads
Do you mean insulating pads for the output transistor?

If so then they are available for most common transistor packages such as TO3, TO220, TO264 and so on.

https://cpc.farnell.com/c/electronic...mal-insulators
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Old 26th May 2019, 11:17 AM   #3
Mark 461 is offline Mark 461
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Morning, and yes I mean those. I believe the ones I took out are mica based though. I really don't want to go through the hassle of ordering since I'll have to import these into my country. I'm wondering if there's an alternative to this. Can I find some sort of plastic or silicone sheet readily available at a store and cut it to fit the transistors?
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Old 26th May 2019, 11:30 AM   #4
Mooly is offline Mooly  United Kingdom
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Transistor insulator pads
I can't just think of anything common that would be suitable. These are specialist items designed to have excellent heat transfer characteristics while also allowing the device to be tightened down correctly without risk of the material compressing and the device become 'loose'. They are also designed to operate at very high temperature if needed.

They look a simple part but are absolutely mission critical in the scheme of things.
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Old 26th May 2019, 11:43 AM   #5
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Mark 461 View Post
Morning, and yes I mean those. I believe the ones I took out are mica based though. I really don't want to go through the hassle of ordering since I'll have to import these into my country. I'm wondering if there's an alternative to this. Can I find some sort of plastic or silicone sheet readily available at a store and cut it to fit the transistors?
What happened to the old ones?

If you can't re-use, maybe its time to donate to this great forum ;-)

Keratherm Transistor Insulators – diyAudio Store

BTW if you re-use the old ones, before switching on, measure resistance between the transistor metal tab and the chassis. It should be many megohms or infinite (often shown as 'overload' on the DMM).

Jan
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Last edited by jan.didden; 26th May 2019 at 11:48 AM.
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Old 26th May 2019, 11:50 AM   #6
Refugee1 is offline Refugee1  United Kingdom
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Most Farnell parts are available from Newark with the same part numbers in many cases. They are both part of the same company.
I would be tempted to open the transistor selector and see if there is an equivalent in an ISO package.
Just type in the spec from the data sheet.
The isolated ones do not command such a high price and best of all they have factory fitted insulating washers. Just a little spot of CPU paste will do the job.
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Old 26th May 2019, 11:54 AM   #7
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Refugee1 View Post
Most Farnell parts are available from Newark with the same part numbers in many cases. They are both part of the same company.
I would be tempted to open the transistor selector and see if there is an equivalent in an ISO package.
Just type in the spec from the data sheet.
The isolated ones do not command such a high price and best of all they have factory fitted insulating washers. Just a little spot of CPU paste will do the job.
The fully insulated ones (often with -F from full pack in the type number) are also much lower in allowed dissipation and, more important, have much smaller SOA. Don't.

Jan
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Old 26th May 2019, 12:40 PM   #8
Mark 461 is offline Mark 461
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Quote:
Originally Posted by jan.didden View Post
What happened to the old ones?

If you can't re-use, maybe its time to donate to this great forum ;-)

Keratherm Transistor Insulators diyAudio Store

BTW if you re-use the old ones, before switching on, measure resistance between the transistor metal tab and the chassis. It should be many megohms or infinite (often shown as 'overload' on the DMM).

Jan
I threw them away when cleaning the amplifier. I didn't know their purpose thought it was just used as a medium for carrying the thermal paste.
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Old 26th May 2019, 12:41 PM   #9
Mark 461 is offline Mark 461
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Quote:
Originally Posted by Mooly View Post
I can't just think of anything common that would be suitable. These are specialist items designed to have excellent heat transfer characteristics while also allowing the device to be tightened down correctly without risk of the material compressing and the device become 'loose'. They are also designed to operate at very high temperature if needed.

They look a simple part but are absolutely mission critical in the scheme of things.
That's what I was afraid of, guess I'll just have to order it then.
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Old 26th May 2019, 12:50 PM   #10
Mark 461 is offline Mark 461
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From the service manual, the receiver uses SK 2SD2560 and SK 2SB1647 transistors. The datasheet says they're 19.9 mm 0.3mm x 15.6 mm 0.4 mm.

Last edited by Mark 461; 26th May 2019 at 12:54 PM.
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