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Anyone Know The Value Of These LD MKIII Resistors?

post #1 of 4
7/10/11 at 1:38pm
Thread Starter 

Recently my MKIII started greatly dimming the sound to the right channel after the unit was on for a bit.  I tried switching the tubes from side to side by that didn't change anything.  Not long after the amp blew up it's pre-amp tubes.  I thought, "Hmm, I guess it was just their time" but after replacing them the next ones blew as well.  I pulled the board out of the chassis and saw that two of the resistors (same value) were completely darkened and ever so slightly burned.  I have no idea why they suddenly decided to burn out.

 

The resistors in question are the ones at the back of the board, just above the the three primary 330uf caps (330uf in the pic but 270uf on my board), that are in line with each other and a third resistor. In the pick bellow the two burned out resistors on my board are the two bright blue ones all the way to the right, to the right of the caps.  I need to know every detail of those resistors so that I can direct replace them.

 

MKIII PCB.jpg

 

You may be wondering why I don't just read the color bands on the resistors but I can't see them properly since it's completely discolored.

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post #2 of 4
7/10/11 at 2:18pm

On version 2 board I believe it is 120ohm resistors in order to use the 6H30 tubes. You may need 5 watts or you can use sand filled resistors as my choice. You may want to raise the resistors a bit off the board so that it will not burn the board.


Edited by john57 - 7/10/11 at 2:28pm
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post #3 of 4
7/10/11 at 11:16pm
You might have more problems than just those two resistors. They might have taken out other things when they went. I'd suspect the power supply for sending too much power to them. Also, they might have killed upstream components when the resistors cooked off.

And what are sand filled resistors? I haven't heard of them.
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post #4 of 4
7/11/11 at 10:00am

sand filled resistors or sometimes called sand block or sand cast is a form of wire wound resistors. They are usually white, rough and boxy looking. I used to built circuits with these type of resistors in the past. You will still find some DIY builders will use this form of power resistors.

 

 

http://www.chokes.com/Sandblock_Resistor.html 

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