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PostPosted: 03 Feb 2017, 11:14 
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maresaldeflota wrote:
http://imgur.com/a/DXloN ( the photos is too big to put here ) the lm317 is from tme texas instr.


is it only one channel which goes up in smoke ? i would take a look at the blue trimpot ....is it trimmed to a value where the mosfet is totally open ? or is there a shortcut there ? are you shure it's a 4,7k and not a 4,7 ? measure it with a multimeter. try to troubleshoot and if it's right mounted, adjust so it has the largest value of resistance for a start, then trim it to half ps voltage.

i would not use the 4k7 trimpot as you ...i would go for at larger value as 47 k or 50 k. you could try to add an 10 k resistor instead of the trimpot just to see if it solves the problem, if so try with differnet values ( 9k, 8 k, 7k, 6 k aso. ) until half voltage at irf's source point is reached. history of this build actually learned some of us, that some tubes need 50 k - 100 k for biasing. when using 'at' or 'ax' instead of 'au' this is an issue, but also with a few 'au' types also.

at left side ( red ring ): did you also burn the connection between the tube and the trimpot ?

at right side: it also looks like this trimpot is floating ...only two connections is soldered ( 1 and 3 ). note: two of the pins ( 1 and 2 ) or ( 2 and 3 ) has to be connected to change the value. which the board layout already is intended for.


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Last edited by KrammeAcoustics on 03 Feb 2017, 12:24, edited 10 times in total.

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PostPosted: 03 Feb 2017, 11:26 
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Ies is mounted correct, and i replace them whit 4k7 fixed and it bourning faster than before. I seted the trims to 10 k both f them, and the left chanel doing flame. And i checked for a short i do twice this schematic, so i cannot understand why....


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PostPosted: 03 Feb 2017, 12:48 
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maresaldeflota wrote:
Ies is mounted correct, and i replace them whit 4k7 fixed and it bourning faster than before. I seted the trims to 10 k both f them, and the left chanel doing flame. And i checked for a short i do twice this schematic, so i cannot understand why....


if you're shure about everything is connected correct, you should try to focus on fake and/or bad regulators and mosfet's or maybe wrong pin out as i told you earlier. here is one of many whom has tried this: https://www.youtube.com/watch?v=vlw88Fq5SmA


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PostPosted: 03 Feb 2017, 13:13 
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http://www.tme.eu/ro/details/lm317at_no ... struments/ there where im buy it from, it says that max amperage is 1.5 A, my source is a 2 A, could be a problem?


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PostPosted: 03 Feb 2017, 13:26 
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maresaldeflota wrote:
http://www.tme.eu/ro/details/lm317at_nopb/regulatoare-de-tensiune-regulata/texas-instruments/ there where im buy it from, it says that max amperage is 1.5 A, my source is a 2 A, could be a problem?


1. i don't know this romanian dealer so i don't know if they sell fake components.

2. no it's not a problem, the lm317 won't reach max. current in this circuit.


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PostPosted: 03 Feb 2017, 13:33 
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Tme is a polish seller :D


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PostPosted: 04 Feb 2017, 05:02 
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I put a new trimmer at 100k but same problem, is there a problem to put at GND the - ?


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PostPosted: 04 Feb 2017, 10:05 
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viewtopic.php?f=10&t=1799&p=29417&hilit=jj+bias#p29417 could be a problem the 10 ohm resistor? Could be used a 40 ohm instead?


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PostPosted: 04 Feb 2017, 13:27 
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maresaldeflota wrote:
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=1799&p=29417&hilit=jj+bias#p29417 could be a problem the 10 ohm resistor? Could be used a 40 ohm instead?


you can always try a 40 ohms, but 10 ohms will be the value for the wanted current ( ccs = constant current source ). i have to say, there must be something wrong with the lm 317 regulator, when it burn the 10 ohm resistor ...you could mount a new lm 317.


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PostPosted: 04 Feb 2017, 14:01 
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I will buy from farnell, which Lm317 to choose?


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