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 Post subject: Could a tube be making a strange noise?
PostPosted: Mar Fri 02, 2018 1:35 am 
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Joined: Feb Tue 10, 2015 2:52 am
Posts: 118
I have a General Electric K-107, and I absolutely love it. Wonderful sound, very clear and clean. I've noticed lately that a weird noise has been coming from one of the tubes. It almost sounds like a light bulb when you shake it, that little metallic rattling sound? I can't pin down which tube (afraid go poke around too much when the radio is on) what might be making this sound? The radio has had all capacitors replaced, and everything aligned and tuned up. What could be making this weird noise?


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Fri 02, 2018 7:28 am 
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Joined: Apr Tue 19, 2011 6:24 am
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Location: 07470
"Singing tubes" are not unheard of, but are uncommon. I had one many years ago, a 6L6G that buzzed on audio peaks. Transformers can also emit audible sounds under some conditions.

To help find the source of your mysterious acoustic emission(s), you might improvise a simple stethoscope or "ear-trumpet" from a length of soft, flexible plastic tubing. Something at least a foot long is best. The inner diameter should be at least 1/8 inch, with 1/2 in. tubing being almost too big to poke into tight places. Tygon tubing is suitable, as is rubber hose (e.g., fuel line) of suitable small diameter.

Put one end to your favorite ear, and move he other end around each suspect tube. Do that in a sequence you can remember or write down. With luck you'll hear the noise more clearly when you get to its source. You may need to move the tubing all around each tube, especially if it has multiple sections.

It goes without saying that you must work in a very quiet place, and also take care to not melt or burn the tubing. That should do it for you.

Happy hunting!

OTH

edited once /OTH


Last edited by OTH on Mar Fri 02, 2018 7:29 pm, edited 1 time in total.

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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Fri 02, 2018 11:55 am 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 2989
Location: Lincoln City, OR
Greetings to OTH and the Forum:

Harbor Freight sells a mechanic's stethoscope. I don't know how well it would work for this application, but it works quite well for locating noisy bearings.

Regards,

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Jim T.
KB6GM


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Fri 02, 2018 6:09 pm 
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Location: Boiling Springs, PA
I have an RCA Globetrotter 7-BX-8J that makes a tingly pinging sound when you turn it on but goes away. Ive heard audio acoustics coming from tubes with no speaker connected. Yeah its possible. I remember back in the day when TVs had CRTs I could tell when a TV was on in another room because I could hear the flyback. When my parents would go to the store looking at TVs it was really annoying hearing all the high pitched frequencies. I bet dogs everywhere are glad CRTs are gone.

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Jeff-W3JKO

"Things are more like they are now than they ever were before" -D. Eisenhower


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Fri 02, 2018 11:58 pm 
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Joined: Feb Tue 10, 2015 2:52 am
Posts: 118
Turns out, it is one of the power tubes, an 80. It also has a brief flash of purple/blue neon-like light when first powered on. It disappears within a second. Should I replace it right away? Or can I wait until it goes out? The radio itself sounds great and almost has no hum at all when the volume is turned down. A very "quiet" radio otherwise.


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Sat 03, 2018 1:12 am 
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Is the first electrolytic cap after the 80 tube much higher in value? Too high of a cap value causes an overload and may make the tube flash. Be sure there isn't purple glow in the tube after it settles down.

One clue may be "quiet" radio, almost no hum.

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Norm


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Sat 03, 2018 1:40 am 
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Joined: Feb Tue 10, 2015 2:52 am
Posts: 118
I tried another 80 tube I had lying around, and it does not have a purple flash. The radio still has the distinctive old radio hum, just a low volume of it. My very amateur self would think it is a healthy radio now.


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 Post subject: Re: Could a tube be making a strange noise?
PostPosted: Mar Sat 03, 2018 2:45 am 
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Location: Tucson, Arizona U.S.A.
The sound the 80 is making is of no concern; the purple flash is.

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Jim Mueller


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