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PostPosted: July 6th, 2017, 4:11 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 270
So 2 of the 6SN7 tubes make a glass ringing sound in the speakers when I tap on them lightly with a screwdriver (kind of like a bonk, bonk, bonk sound as I tap).

The other two make no noise.

I have never done this before, so I don't know if they did that when they were new.

I clearly didn't hear any pops or cracks.


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PostPosted: July 6th, 2017, 5:00 pm 
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Joined: October 21st, 2013, 6:53 pm
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Just to clarify something:

Those four 6SN7 tubes are supposed to make no noise when the amplifier is on, and you tap on them?

If they do, then they are microphonic, and that is some sort of developmental defect?


Thanks,

Chris


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PostPosted: July 6th, 2017, 5:07 pm 
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Joined: April 22nd, 2013, 12:58 pm
Posts: 178
Your description in the prior post (....boing, ringing,....) is normal and expected.
ALL tubes are microphonic, to some extent.
Microphonic noise produced in the two input tubes will be more noticeable, because there is more gain downstream to amplify it.

chris1973 wrote:
Just to clarify something:

Those four 6SN7 tubes are supposed to make no noise when the amplifier is on, and you tap on them?

If they do, then they are microphonic, and that is some sort of developmental defect?


Thanks,

Chris


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PostPosted: July 6th, 2017, 6:12 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 606
I would replace all four 6SN7s. If the crackling continues, I would visually inspect all solder joints for loose joint.

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PostPosted: July 7th, 2017, 5:05 pm 
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Joined: March 2nd, 2013, 2:43 pm
Posts: 155
Location: Potomac, MD
Most tube amps are capacitor coupled between the driver and output tubes. If this is the case for your amp you might try removing the driver tubes to see if the popping continues. If it does, the output stage is likely involved and the driver stage is probably not. Also, identify which channel is popping. If both are popping, perhaps a filter capacitor in the power supply is shorting. If the popping is a regular occurrence, I would be happy to invite you over to my house to see if we can determine what is causing the fault.

David


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PostPosted: July 7th, 2017, 5:26 pm 
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Joined: February 28th, 2013, 3:31 pm
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My strong suggestion is to take David up on his offer. You would be hard pressed to find someone who has more knowledge of tube circuits than David.

Tom


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PostPosted: July 7th, 2017, 7:23 pm 
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Joined: October 21st, 2013, 6:53 pm
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dberning wrote:
Most tube amps are capacitor coupled between the driver and output tubes. If this is the case for your amp you might try removing the driver tubes to see if the popping continues. If it does, the output stage is likely involved and the driver stage is probably not. Also, identify which channel is popping. If both are popping, perhaps a filter capacitor in the power supply is shorting. If the popping is a regular occurrence, I would be happy to invite you over to my house to see if we can determine what is causing the fault.

David

Thanks Dave, It's really sporadic. I t hasn't happened in several days. Let me feel it out for a little while, and I will keep you informed.

Chris


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PostPosted: July 8th, 2017, 10:10 am 
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Chris,

I understand your desire to debug the amp yourself. But, when an expert like David offers to help, you should take it. Think of it as an opportunity to learn about the amp from a guru.

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Shashi


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PostPosted: July 8th, 2017, 11:38 am 
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Location: Parkville, Maryland
I second the motion. David Berning is an accomplished tube amp designer with the patent to prove it and has manufactured products on the market.

He is a genuinely nice guy and if he offers to help -- he means just that -- to help you.

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Walt


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