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I have a graaf 13.5b preamp feedback.

I have a graaf 13.5b preamp. I recently changed tubes. (sovtek 6922 to miniwat e88cc). When i use the input selector of my preamp i get a increasing hum from my speakers. I had no problem before the change of tubes. The techinician who checked the preamp found nothing wrong.
Please advise.

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Hi Geo,

Did you solve the problem, By the way I'm thinking buy a graaf 13.5B II, Can you tell me your experience? what you think about this preamp? it is quiet did the tubes make any noise (HUM, HISS) I have a very sensitive speakers (105db). Please hekp me to decide.

Posted on Mar 14, 2010

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One of the new tubes was faulty.

Posted on Jun 01, 2009


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Next, the tube filiments are powered by AC voltage, and there is a control on the chassis for balancing it in order to reduce the hum. It could be toast or mis-adjusted. There could be a tube or other component problem causing your hum. The DC power supply could have faulty filter capacitors.

Another source of problems in these amps are the carbon resistors that introduce static noise in the audio. These should be changed to much better carbon film resistors.

If you are not comfortable working on electronic equipment with voltages in excess of 300VDC you should bring it to a pro audio repair shop.

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