Please help with MPX3 problem
Mar 20, 2006 at 8:27 PM Thread Starter Post #1 of 10

DavidNighorn

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Hello all,

I have been lurking and learning for over a year now. Nearly 9 months ago, based on rave reviews here, I bought the Singlepower MPX3. Needless to say, it is absolutely wonderful.

But now I have a problem. Just in the last few days, I have started to hear static from the amp (via the phones). It sound is constant but varies - kind of like the sound of rain and wind on a window. The static varies in loudness as the volume is adjusted and is present with both sources. In fact, the static is there with no sources connected. It is also there even when I disconnect the power cable (while the caps still have power). Switching phones does not change anything either.

Clearly, the source of the static is somewhere in the amp. With 700 hours on it, do you think that I could be losing a tube? Is such a noise consistent with tube failure. My tubes look fine visually. One other data point, the volume knob position required to get a particular output sound level has gone down quite a bit from normal. IOW, I don't have to turn it up much to get the same levels as I used to get.

Any help would be appreciated. I love this amp but I cannot stand to listent to it right now with the static.

David
 
Mar 20, 2006 at 8:50 PM Post #2 of 10

Rob N

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Sounds like tube noise.

Have you tried switching the tubes to different positions?

A tube that's noisy will work fine as an output tube but you'll hear the noise if it's used as an input/gain tube.
 
Mar 20, 2006 at 8:57 PM Post #3 of 10

DavidNighorn

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Which of the tube positions is the ouptut one?

I took the suggestion by randomly switching the tubes so that none are in their original position. This seems to have helped. I'll have to let the entire rig warm up properly before I can say this definitively.

Never heard of tube noise until today. Since this set in in just a few days, is it still indicative of an impending tube failure?

David
 
Mar 20, 2006 at 9:09 PM Post #4 of 10

Voltron

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It sure does sound like the tubes. The front-most/left-most tube is the gain tube, while the other two are L/R output tubes. Hopefully you recall which one was in the gain position that gave you the noise, and you should probably replace it. If you have a whole different set of tubes, I would try that and see if it sounds clean again. Then, you can replace the gain tube in turns to find the one that causes the problem. If you are using the stock Electro-Harmonix tubes, my set had two 6SN7s with one number designation and one 6SN7 with different number designation. I am not at home so I cannot tell which was which. Good luck figuring it out.
 
Mar 20, 2006 at 9:46 PM Post #5 of 10

Rob N

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Some tubes become noisy after only a short time of use.It doesn't indicate that the tube will soon fail.In my experience the vast majority of tubes stay quiet.
 
Mar 20, 2006 at 10:10 PM Post #6 of 10

Hirsch

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Quote:

Originally Posted by DavidNighorn
Never heard of tube noise until today. Since this set in in just a few days, is it still indicative of an impending tube failure?


That depends on the noise. Intermittent loud "pops" can be indicative of arcing, and the tube should probably not be used any more. Sooner or later it will short, and bad things could happen. Other noise can simply be a noisy tube. It will need to be replaced, simply because it interferes with enjoyment of the music. Other noise might be microphonics. Tubes used for voltage gain are much more vulnerable to this than tubes used for current output, as a rule. If noise is heard when you tap on the chassis of the amp next to a tube, that's probably the case. Tube dampers might help. Finally, you can get noise with a bad connection between the tube and socket. Worst case would be a bad tube socket, but that's not likely. If a bad connection is going on, cleaning the tube pins with Caig DeOxit or something similar might fix the problem.
 
Mar 21, 2006 at 3:52 AM Post #7 of 10

BrianS

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i hope it's just a tube issue, if not Mikhail will help you out. ive had my mpx3 probably around 2 years now and the amp and the rca cleartop 6cg7s still work well even though the gain one is a little black near the top. i've never heard tube "noise" so i can't comment on that. good luck
 
Mar 21, 2006 at 12:16 PM Post #8 of 10

DavidNighorn

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The problem is almost certainly tube noise. After swapping the tubes around, the noise went down to nearly inaudible. It is still there though if I turn the amp way up. Since such volume levels with music would be deafening, I consider the problem temporarily solved.

Now I need to get a new set of 6sn7 tubes. Besides the EH new stock tubes, any reasonably priced alternatives?

David
 
Mar 21, 2006 at 1:35 PM Post #9 of 10

jamesp

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Quote:

Originally Posted by DavidNighorn
The problem is almost certainly tube noise. After swapping the tubes around, the noise went down to nearly inaudible. It is still there though if I turn the amp way up. Since such volume levels with music would be deafening, I consider the problem temporarily solved.

Now I need to get a new set of 6sn7 tubes. Besides the EH new stock tubes, any reasonably priced alternatives?

David




Check the for sale forum, I just bought some lastnight.
 

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