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Old 14th May 2008, 07:51 PM   #1
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Default constructed with fake mj15003-4

i constructed a P68 amplifier on a vero board just for testing ....i used MJ15003-4 and made a construction that is based on one pcb and supports 10 transistors for output totaly.

all tests went just fine and produced about 225w with 60 volt rails .....

while constructing, touching the output transistors was enough to remove the "on semi" logo from them .....

finished the project test it more or less looks ok but !!!!! the transistors are fakes i open one of them and the die inside is smaller than a 2N3055 and about the one third of an original on semi that i have ....

what should i do ????let them there or remove them ???

the particular device was only made for testing but there is a chance that i want to use it some time .....
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Old 14th May 2008, 10:00 PM   #2
jaycee is offline jaycee  United Kingdom
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If they're fakes they aren't going to survive the amp when it's really put to use. They will eventually go up in smoke.

Keep them and use them for some lower-power amp.
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Old 15th May 2008, 10:11 AM   #3
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hi sakis,

can i see the schmdit? just curious.....

thanks...
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Old 15th May 2008, 10:15 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
is your amp intended for driving 4ohm speakers?
It looks like the power specification is 225W into 4r0. (42.4Vpk)

If this is the case, then to provide reliable power into a reactive load the amp should be capable of supplying near full voltage into half load impedance or better.
I suggest you are looking for 400W into 2r0, (40Vpk) -0.5dbV ref 225W into 4r0.
But, this allows the equivalent stress for near 45degree phase angle load.
If you intend to make it suitable for 60degree phase angle load then 1r5 would probably be a better test resistance. This time allow a voltage droop to around -0.8dbV ie 38.7Vpk.

Both these high current tests should be done for only one or two seconds, just long enough for the power supply to settle and the instrumentation to gather data values.
If you want to increase the test stress then allow the starting temperature of the heatsink and device to be higher than your summer ambient.
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Old 15th May 2008, 11:26 AM   #5
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Default thanks every body

i am going to relace all of them since the provider is willing to replace them for real on semis .....( for free !!!!! )

i went to the shop crunked open in frond of the owner a fake mj15003 and explain whats wrong with it ....

the die of my fake transistor was the on third in size compaired even with a 2N3055

any way will replace them and see .....

andrew ..... i dont relly get it ..... 225w was mesured at 8R jesus andrew there is 10 outputs per board .....i have a swing of almost 46 volts

anyway the point is not really if makes 225 or 180 or 250w at 8R the point is to be stable also
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Old 15th May 2008, 11:44 AM   #6
AndrewT is offline AndrewT  Scotland
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Default Re: thanks every body

Quote:
Originally posted by sakis
..... i dont relly get it ..... 225w was mesured at 8R
The point is:- will the fake or real output stage survive the stress of driving a reactive speaker.

You need to stress the output stage to a similar level that a reactive speaker will impose.
I gave you a method of determining if the amp and it's power supply is up to the job of driving a stressful load.

Now that you have confirmed 8ohm, then your test load for 45degree capability should be 4r0 (to 40Vac) and for 60degree use 3r0 (to 38.7Vac).

This does not exactly duplicate the stresses involved in driving a severely reactive load, it puts most of the high current into the power limitation region of the SOAR, whereas the reactive load moves the worst operating point down into the region of secondary breakdown.
But it's the best I have come up with as a guide to amp capability.

Quote:
produced about 225w with 60 volt rails .....
could you explain how you get an output of about 60Vpk from +-60Vdc supply rails?
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