Re: Mosfet Power dissipation question
Yes the new NF replacement I blew also. The original I blew touching the speaker cables and the NF I blew by touching the DC offset leads!
I have found a source who claims to sell originals. But as mentioned I need to understand this Power Dissipation thing before I decide on the transistors as I'm worried about the heat produced
holmzy
Senior Member
Last Activity: 12-23-2023, 01:49 PM
Joined: 11-23-2009
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Re: Mosfet Power dissipation question
LOL I was doing that then shorted the leads and blew the MOSFETs!...Leave a comment:
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Re: Mosfet Power dissipation question
I shorted the test leads by accident! The pot is fine...Leave a comment:
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Re: Mosfet Power dissipation question
Yes I can. I measured it after 15 minutes of the amplifier running realised the DC was high (speakers were not connected) and went to adjust it and it popped
I dont know the actual temps. I put my hand across the heatsink and NF was easily higher. The difference was very hot and very very hot if that makes sense...Leave a comment:
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Re: Mosfet Power dissipation question
The 0mv was the DC offset not the bias.
On the original transistors the bias was set to 160mv and the DC was set to 0mv (or as close to it).
The NF replacement transistors the bias was also set to 160mv but the DC was measuring 100mv. It was running like that for 15 minutes and I noticed it was very hot compared to the original only a few days back.
I thought it was running hot due to the high DC so when I went to adjust it unfortunately the DC wires touched between the channels and shorted the MOSFETs....Leave a comment:
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Re: Mosfet Power dissipation question
Thanks for the replies.
There is no thermal grease just thermal pad and a screw. They were both mounted identically and exact same amp. It just seemed the NF was noticeably hotter at the same bias and volume.
Only difference was the NF bias was 100mv and the NE was 0mv bias. I was adjusting the 100mv before it blew (again)
If high DC offset has a serious affect on the MOSFET then I guess that answers that if not then I need original MOSFETS as replacements run a bit too hot!...Leave a comment:
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Re: Mosfet Power dissipation question
But original questions still remains about the power dissipation factor. I still dont understand it and there is a big difference between the 95w and 130w. I can get the original part back in but at greater cost. I'm just trying to figure out if the extra heat was due to the newer NF MOSFET having 95w and old having 130w.
Would higher PD make it run hotter or cooler?Leave a comment:
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Re: Mosfet Power dissipation question
Well I got the amplifier and it was working with original transistors, I set all the bias and DC etc then I managed to short the cables.
So I ordered the NF replacement and noticed it was hotter than before and the bias was very high on previous setting, after adjusting it down I noticed it was hotter and as I was doing the DC I damaged to touch the leads and another short!
Both times the only damage was to the output MOSFETs...Leave a comment:
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Re: Mosfet Power dissipation question
Hi, are you saying the DC offset can affect the temperature of the MOSFET? I just measured using my hands.
I dont know if it was drawing more current but like I mentioned I did adjust the bias according to the manual.
I did notice I had to turn the trimmer pot for the idle right down as it was very high with the NF (newer) MOSFETLeave a comment:
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Re: Mosfet Power dissipation question
Also what do you mean the range is fairly large?
They were both operated in the same amplifier and bias set the same etc but I noticed the NF was hotter. I explained it again just so it was clear.Leave a comment:
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Re: Mosfet Power dissipation question
Wowzer information overload!
I would love to fully understand it but as mentioned before the service manual states the idle at 160-180 and both times was set to 160 but was noticeably hotter with the NF.
I have attached link to service manual. If NF is an upgrade 95w is better? Lower numbers are better? Thanks
[URL="https://www.hifiengine.com/manual_library/nad/c300.shtml"]https://www.hifiengine.com/manual_library/nad/c300.shtml[/URL]Re: Mosfet Power dissipation question
WowzerLeave a comment:
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Mosfet Power dissipation question
Hi guys,
I have a Nad C300 with the outputs blown. It uses original part STP55NE06L which is not readily available. The suggested replacement STP55NF06L is readily available. But I noticed that the amplifier now runs hotter even with the same bias etc.
The data sheet states the original is 130w power dissipation and the replacement is 95w. I dont understand the other parameters either
Can anyone please help me to understand if this is why it is running hotter than before? -
Re: Rotel RA-940BX distorted sound
got switch spray from maplins. sprayed everything no change what so ever!Leave a comment:
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Re: Rotel RA-940BX distorted sound
I will give maplins a shot later hopefully and yes I do mean bias adjust test points 1-4Leave a comment:
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Re: Rotel RA-940BX distorted sound
I get 0v across the test terminal! I will have to invest in this detox spray. If I could test the switch via speakers or something would be good to confirm fault. yes the relay does clickLeave a comment:
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Re: Rotel RA-940BX distorted sound
hi I did try switching back and forth a lot and air blew the switches. Could this explain the 0v at the bias adjust?Leave a comment:
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Re: Rotel RA-940BX distorted sound
hi guys, the smoothing caps are fine i have replaced them alread no effect. ac3 is mains cable live and ac4 is connected to ac3 via power switch and capacitor. ac4 is live mains IN 240v on transformerLeave a comment:
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Re: Rotel RA-940BX distorted sound
inside the unit itself where the mains wire goes in measure 240 exactly. could it be the bridge rectifier? its a PBPC803 on the sm manual its suppose to be KBPC802. could that be limiting the voltage? I really dont understand what could be causing the power loss!Leave a comment:
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Re: Rotel RA-940BX distorted sound
I have just seen that ac4 is actuay connected directly to ac3. so should be already set on 240v right?Leave a comment:
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Re: Rotel RA-940BX distorted sound
You may be on to something here. Im in UK. the back states for 240v. but inside is set on 220V. The ac input measured is indeed 240v...Last edited by holmzy; 08-25-2015, 04:52 PM.Leave a comment:
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