Transistors on FET amplifier board running hotter then others on same heatsink

Thread Starter

Meerkat 67

Joined Jan 29, 2015
36
I put together a power amplifier with FET output boards that has a couple of the transistors on one of the channel boards running hotter then any of the others on the same channel as well as the other channel. The variance is about 10-15 degrees on my laser and does fluctuate over time rising and then cooling down. I built a few amps with the same board and never had this issue. The sound does not change in any way that I can hear. Just wondering if this is normal as these are Chinese boards. I do not have a schematic but have indicated the link to the boards purchased. Anyone have thoughts on this issue Thanks Wayne

https://www.ebay.ca/itm/Mono-Channel-Amplifier-Amp-Board-10000-UF-2-150W-FET-Power-Amp-with-IRFP250-6/222078905084?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
 

Audioguru

Joined Dec 20, 2007
11,251
I guess the manufacturer or the circuit poorly matches the Mosfets causing some to be hotter than others.
Did you notice that the distortion is rated only at a puny 20W? Then maybe it distorts badly at higher power.
Why is the frequency response not mentioned?
 

Thread Starter

Meerkat 67

Joined Jan 29, 2015
36
Are they as securely pressed against the heatsink as the others?
Thanks Albert.. Some of the transistors were not as tight as others so I redid all of them.. Temps have come down so that appears to be the problem.. Will monitor this on the test bench.. I obviously overlooked this, must be getting old.. Cheers Wayne
 

Thread Starter

Meerkat 67

Joined Jan 29, 2015
36
I guess the manufacturer or the circuit poorly matches the Mosfets causing some to be hotter than others.
Did you notice that the distortion is rated only at a puny 20W? Then maybe it distorts badly at higher power.
Why is the frequency response not mentioned?
I have used other boards from another supplier and did not hear any distortion at very high power levels using my AR3A's as test speakers. I am not sure why the frequency response is not mentioned in this particular case. I only build these amps for a hobby and do not have access to distortion meters and other test equipment. I did find a solution to the temp problem by tightening all the FETs on that one heat sink. Perhaps you are right with regard to the matching and I appreciate your views, Thanks Wayne
 
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