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Author Topic: Noisy tube amp  (Read 9468 times)

Offline confused

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Noisy tube amp
« on: January 05, 2010, 09:23:46 PM »
I spent the day with a buddy working on my Akai amps.  1 amp has an intermittent noise, just a little background clicking.  This is unaffected by the volume control.  After the amp has run for several hours the noise stops.

We checked all tubes, coupling & power supply caps, amd bias resistors.  Moved components around to check for cold solders and cleaned switches and tube sockets.  The noise persists!

Anyone out there have any suggestions about whewre to look next?

THX for any suggestions?
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Offline OCCD

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Re: Noisy tube amp
« Reply #1 on: January 05, 2010, 11:34:06 PM »
Did you run the tubes from the good amp into the suspect amp? That is a good place to start the elimination process. That is unless you have already done that.
« Last Edit: January 05, 2010, 11:39:21 PM by OCCD »
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Offline F1nut

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Re: Noisy tube amp
« Reply #2 on: January 06, 2010, 01:06:41 AM »
Even though you checked them, I would suspect a cap or possibly a tube going south, but more so, a cap.
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Offline confused

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Re: Noisy tube amp
« Reply #3 on: January 06, 2010, 06:00:28 PM »
Thanks F1nut & OCCD for the suggestions.  Tubes were traded right to left, noise did not move.  Also we physically removed the Caps And Resistors and temporarily replaced them to no avail.  Using a scope we were able to find the noise on 1 side of a resistor in the bias voltage divider, but not the other!  Replacing that resistor did not fix it. 
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Offline F1nut

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Re: Noisy tube amp
« Reply #4 on: January 07, 2010, 12:47:40 AM »
Quote from: confused on January 06, 2010, 06:00:28 PM
Thanks F1nut & OCCD for the suggestions.  Tubes were traded right to left, noise did not move.  Also we physically removed the Caps And Resistors and temporarily replaced them to no avail.  Using a scope we were able to find the noise on 1 side of a resistor in the bias voltage divider, but not the other!  Replacing that resistor did not fix it. 

Hmmm....in that case, good luck!
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Offline confused

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Re: Noisy tube amp
« Reply #5 on: January 07, 2010, 11:39:16 AM »
Thanks F1nut, the noise is really buried behind the signal in all but very quiet passages.  May have to listen to more dynamically restricted music.  Trying a new tact today.  As the noise stops after an hour or two of use, going to warm up amp until noise stops then spray individual components to cool them until noise comes back (hopefully).  Will get back with the results.
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Offline F1nut

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Re: Noisy tube amp
« Reply #6 on: January 07, 2010, 06:04:17 PM »
That's a good plan of attack.
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Offline confused

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Re: Noisy tube amp
« Reply #7 on: January 08, 2010, 04:05:27 PM »
SUCCESS!!! ;D  Turned out toi be a wiring problem.  Bypass cap not connected to ground.  By the way, while my buddy had it he checked frequency response and found it nearly flat to 30Khz he says.
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