hi mighty gurus i'm here asking for your extremely large knowledge. just finish to rebuild a vintage Punch 800.2 new outputs new psu mosfets and few smd resistors and transistors by the book, now is working smoothly idle @ 0.58 amp consumption. but at few minutes getting hot @ 85° c after 5 minutes running at 4 ohm per channel. is this a bias problem or mismatch/ low quality components perhaps ? outputs are combined IRF9640 by Vishay IRF640N by IR thank's in advance.
Interesting ! but have replaced before 640's for 640N and have no issues. maybe they change something. btw anyone knows where i can get those original IRF640 beside eBay ? most of them are fake ones. tyvm.
Digikey
http://www.digikey.com/product-search/en?vendor=0&keywords=irf640pbf
Those what you are looking for?
http://www.digikey.com/product-search/en?vendor=0&keywords=irf640pbf
Those what you are looking for?
I have heard this many times but never experienced it.
I have used 640N and 9640N in amps many times and have had zero issues. There is still amps working that I have repaired years ago with the "N" FET's.
I don't think you would want N and non N in the same channel as I have never tried that.
How did you set the bias?
I have used 640N and 9640N in amps many times and have had zero issues. There is still amps working that I have repaired years ago with the "N" FET's.
I don't think you would want N and non N in the same channel as I have never tried that.
How did you set the bias?
Check for bias runaway by turning the amp on COLD and check the B+ current (0.58A is what you said) then let it sit with NO SIGNAL for an hour, then check to see if the B+ current has increased more than COLD. Check to see that the bias tracking transistors on each channel are in contact with the heatsink. I think they are TO-92 devices. If the HOT bias is too high, just set it lower when COLD.
To check the output circuits, measure the efficiency. Run at full power both channels (Pout), measure B+ voltage and current, calculate the input power Pin=V*I.. If the efficiency (Pout/Pin) is more than 60%, your amp is ok.
To check the output circuits, measure the efficiency. Run at full power both channels (Pout), measure B+ voltage and current, calculate the input power Pin=V*I.. If the efficiency (Pout/Pin) is more than 60%, your amp is ok.
Ok already changed the 640N and place 640PBF. Cold idle amp decreased to 0.28 running full power for 12 minutes n'd almost burn my hand @89° test amp consumption was , .89 amp hot. If i set lower bias sound at low volume is kinda distorted. All the bias transistors msp A06 and the mspA56. the efficiency test. Less than 50% =\
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Sent from my GT-I9300 using Tapatalk
The bias drift might be improved if you find the bias tracking transistors near the MESA/Heatsink and bend them over to make contact with the hot heatsink. Use thermal grease if you have it. It will be a NPN transistor, probably MPSA06 or MPS6521.
The heatsink will go up to 90 degrees celcius and thermal protect when run at full power so that does not sound so bad. The efficiency could be better. Make sure you measure with about 1% THD clipping, 1kHz, and measure the B+ voltage right at the amp input terminals. The method of current measurement must be accurate - not just reading the dials on an ASTRON. Even so, if it doesn't blow up at full power and makes it to thermal I think you fixed it ok and would go ahead and run it.
The heatsink will go up to 90 degrees celcius and thermal protect when run at full power so that does not sound so bad. The efficiency could be better. Make sure you measure with about 1% THD clipping, 1kHz, and measure the B+ voltage right at the amp input terminals. The method of current measurement must be accurate - not just reading the dials on an ASTRON. Even so, if it doesn't blow up at full power and makes it to thermal I think you fixed it ok and would go ahead and run it.
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