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New MiniMax, only sound from right channel.

post #1 of 9
2/27/11 at 4:34pm
Thread Starter 

Tubes glow, so I'm getting power. I've checked all the terminal blocks and I know I'm getting proper signal from source.

The left tube bias is also stuck at 9.5 volts and no amount of turning the trimmer (RA1L) makes any difference. (all the way to the clicks in both directions) All the others adjusted perfectly as suggested. The right channel works great..

 

You can't see it in the photo, but there is another jumper at RB14L, just like the one you see at RB14R.IMG_20110227_162031.jpg

IMG_20110227_162215.jpg

 

Help?

 

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post #2 of 9
2/27/11 at 4:46pm

I can't see from the photos, but would you please check to see if RA8L is the same as RA8R.  Likewise - is RA9L the same as RA9R?

 

If that doesn't pan out, then you've got a good start - the Right channel works, the Left doesn't.  So, check every single resistor past the tubes (after checking the above), from the Right channel to the Left (measuring Ohms with the Power OFF).  Essentially, the Right channel is different from the Left.  We need to find out what's differnt with the Left channel.smily_headphones1.gif

 

 

P.S. I just looked at your top photo and the headphone plug looks a little weird.  Are you sure you've inserted it all the way?  That's probably a stupid suggestion, but I thought it was worth trying.wink.gif

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post #3 of 9
2/27/11 at 5:05pm
Thread Starter 

HI Tom, Yes, RA8L/R, and RA9L/R  are both the same. 

The Headphone jack is not a stupid suggestion, in fact that is what I thought the problem was the entire time, but alas, not so simple.

 

What about the left tube  not biasing with that trimmer,  whereabouts on the board should I looking for something that would cause that?

Thanks for your help so far,

 

-B

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post #4 of 9
2/27/11 at 5:10pm
Have you swapped the tubes?
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post #5 of 9
2/27/11 at 5:13pm

Check QB2L 

Here's an image of the board:http://www.diyforums.org/MiniMAX/board/MiniMAXoverlay.jpg

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post #6 of 9
2/27/11 at 5:51pm
Thread Starter 

*face smack*. I've been staring at this for 5 hours, how did I miss that. Should have walked away for a bit, and it would have jumped out at me. 

Thanks for the extra pair of eyes!

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post #7 of 9
2/27/11 at 6:01pm
Nice catch rds!
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post #8 of 9
2/27/11 at 6:24pm

Yep - rds nailed it!! biggrin.gif

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post #9 of 9
2/27/11 at 6:37pm

nailed it.jpg

 

Seeing these pics makes me want to build another one - such an enjoyable amp to build ...and listen to of course

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