500W PA amplifier with Limiter

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viki_v2

viki_v2

Member
Joined 2009
irvynejay said:
I agree with NIX better check your work many DIYER's and me have made this amp with out problem...maybe you have little glitch on placement of the parts mje 340/350,15032/33 are tricky you have to be more careful

MJE350 is PNP
MJE340 is NPN
MJE15032 NPN
MJE15033 PNP

if its original:vampire:
if fake you got wrong orientation of pins
Click to expand...

cant be fakes, got MJE350, MJE340 ,MJE15032 ,MJE15033 as samples from on semi, checked complete layout for shorts, cold solder, parts placement.
Please tell bce of 2n5401 and 2n5551.
 
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mj777

Member
Joined 2010
many thanks to Andrewlebon and irvynejay you two are right the problem is with my 2n5401/5551, also those mje340and 350, when i replaced it the B500 works perfectly, just the thing is that i also change the toshiba 5200 and 1943, cause it was affected due to the failure of the defective transistors.
 
M

mj777

Member
Joined 2010
dear viki better check or replace ur transistors as what is being advice by others, like irvynejay and AndrewT, the problem is only on those parts, especially the 2n5401/5551, better to be carefull and check the pins of these transistors CBE/EBC by the multimeter, before you fix it in the board, when u fix it in the wrong way it will damage all your other transistors like what happened to me. i did changed all the transistors and the B500 works perfectly. i've a dc offset of 4.8 milivolts and in Q5 i have 1.94 volts( C to E ).

regards,
mj777
 
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mj777

Member
Joined 2010
B500 after changing transistors

thanks for all the diyers who had help me with there precious advice the B500 is now working perfectly nice sound DSC03133.JPG
 
viki_v2

viki_v2

Member
Joined 2009
I have may be found the problem,
I removed 2n5401 next to negative terminal on pcb, Switched on and there was very crystal clear sound. No humming , no distortion. No heating of resistors on psu board.
Played for 2 to 3 hrs.

After some time switched on, No sound 22E on psu gets very hot, cannot touch. I remove collector leg of mje15033 , there is sound but again very distorted.
 
viki_v2

viki_v2

Member
Joined 2009
Hello,
Finally rectified the problem, paralleled a 4k7 2w resistor to a 4k7 2w resistor near mje340 above 2sa1943.

Now the sound is clean, Still one problem persists, On low volume the sound is nice, But as volume increase, the sound starts to distort.

My psu is 37-0-37 3 amperes. Running two transistor pair on amp board.

on pcb the resistor is given 4k7 2w and schematic shows 2k2.
 
viki_v2

viki_v2

Member
Joined 2009
Dc ofset is 9.5 mv. 37-0-37 is dc after rectification as i am using only two pairs of transistors . for 37-0-37 i will need 1k2 2w . This is where i made the mistake, i did not calculate r 24 and 25 as per voltage. But it is working fine now.

thank you all the fellow diyer's who were patient enough to help a newbie like me.

The sound is loud and very clear.
 
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