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Tube amp produces loud hum in one channel please help - Page 2

post #16 of 27
12/22/10 at 11:01am
Thread Starter 

I found that one green terminal block sitting on top of the NFB output was very loose. While I touched it just now, it came off.It is the block in the amp board that is closest to the volume pot/NFB pot (in other words, the amp board in the lower middle column, having the amp front facing you). However, since the NFB has been inactivated in this Bijou amp, does it matter? I can try to glue it back and maintain the contacts.

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post #17 of 27
12/22/10 at 11:02am

The screws you touched, particularly near the bundle of wires on the right, are the signal wires.  Something probably got knocked loose.  Check the wiring on the potentiometer as well.  The wire may have broken off on the tabs.  There are a couple of wires that look to be hanging on for dear life or have broken, on the potentiometer.  A black wire and a white-ish wire.

 

I also don't like that the signal wires run so close to the power and heater lines.  The heaters are AC, but that would only induce hum along with audio.

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post #18 of 27
12/22/10 at 11:10am
Thread Starter 

Bingo! holland you almost found out this the same time as my seller. He just pointed out at the volume pot so I checked.

It is probably due to a loose signal wire (green) connected to the volume pot. What can I use to attach it back? I can not solder and do not have a solder gun....

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post #19 of 27
12/22/10 at 11:14am
Thread Starter 

The green signal wire connected to the volume pot is completely off. Don't remember pulling on it, but it has to be myself.

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post #20 of 27
12/22/10 at 12:49pm
Thread Starter 

Thank you Jake and holland. I think this should fix the hum. I will report back once I have a result.

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post #21 of 27
12/22/10 at 7:30pm
Thread Starter 

I soldered the loose signal wire back to the volume pot.

 

However,I could not solder back the terminal block. Its base has three contact points, and I was not fast enough to fill all three contact points with solder to re-attach the terminal block.

 

Please advise me what to do. Or maybe this is beyond me as a beginner?

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post #22 of 27
12/22/10 at 9:23pm
Quote:
Originally Posted by zzffnn View Post

I soldered the loose signal wire back to the volume pot.

 

However,I could not solder back the terminal block. Its base has three contact points, and I was not fast enough to fill all three contact points with solder to re-attach the terminal block.

 

Please advise me what to do. Or maybe this is beyond me as a beginner?


I hold the block in place and then solder the middle pin.  I put solder on the iron tip, a blob.  hold the block in place, and hit the middle, and it will tack it down.  Then position it the way you want, as I like things to line up properly.  After that, let it cool a bit, then solder down the other pins, with a blob.  If all looks good, fill it, one pin at a time.

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post #23 of 27
12/23/10 at 8:00am
Thread Starter 

Thanks holland. I will try.

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post #24 of 27
12/23/10 at 8:03am
Are you trying to solder it from the top of the board? By that I mean, fill the holes and jam the part into them?

If so, that will not be successful. You will need to access the back of the board and use the technique that Holland recommends.
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post #25 of 27
12/23/10 at 8:40am

Something to consider is changing this thread's title to incl like "need a bit of wiring help in Houston" to fish for a head-fi DIYer in your area.

Good that you're trying to fix this yourself, but better I'd think if some nice person close by could take a peek.  Just a thought.

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post #26 of 27
12/25/10 at 2:31pm
Thread Starter 

Thanks everyone for helping here. We fixed the problem. As holland and my seller pointed out, the hum and lost of signal was due to a terminal block in one of the amp board and a signal wire connected to the volume pot. We soldered back both and got sweet music from both channels with no hum. My seller, Shinyfalcon (my local builder), and I worked closely together and solved the problem. 

 

May you all have a joyful new year!

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post #27 of 27
12/25/10 at 5:23pm
That is great news zzffnn!

Perfect way to close out the year and start the new one.

May you have a joyful (and tuneful) new year as well.
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