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Thread: The smell test

  1. #1

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    Default The smell test

    Just looking for some opinions and experiences. I know eventually it will have to be sent in for service.

    The last two times I fired up my Dared I-30 tube integrated after about 10-15 minutes of playing I smell something hot, not necessarily pungent burning type smell but something hot smelling and the left channel starts crackling and hissing. It uses (4) 6L6 GC power tubes 2 for each channel in a push/pull configuration. (2) 12AX7's and (2) 12AU7's for the input section.

    Both times this has happened I have shut her down and after a few minutes of cooling down I start sniffing around seeing if I can smell a cooked component as well as doing a thorough visual inspection. No cooked smell or visual damage. Today I even took the back off and performed the smell test. Nothing smelled funky at all.

    I suspect a bad 6L6 power tube. I need to roll another pair in the left side to see if that takes care of it. I should have done that today to rule out the power tubes, but it's already put away.

    I know this is NOT the way to diagnose a problem. But I think there would be a cooked smell inside the amp if something was toast.

    What do you think?

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    Can you look at the resistors/caps by pulling the bottom plate? I'm guessing by your post that it does not smell like toobs due-- you know,, that tooby smell? Good luck--let us know.
    JC approves....he told me so. (F-1 nut)

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    I did pull the bottom plate George, looks like new, smells like new.

    No not the typical hottish metallic smell of fully warmed up power tubes. It's definitely a hot burning smell, just not a putrid smell. Almost similar to melting plastic, I guess. Maybe a cross between a card board box burning with a hint of hot plastic. The tube sockets are ceramic. It's also a self biasing unit, not manual.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    Can you test the tubes? I had a tube that kinda exhibited the same symptoms as you are having-- turns out it was a bad plate to ground issue with the tube IIRC--good luck!
    JC approves....he told me so. (F-1 nut)

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    Maybe a transformer fixing to take a dump? Happend to me,clue was the crackling noise you spoke of...they kind of smell at first and when they go it stinks bad...just a thought.

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    No way to test other than rolling in another pair. Maybe I'll put the original Ruby's in and see what happens.

    I did cook a tube once on my other unit which is manual bias. Didn't realize until after I cooked a nice 50's RCA 6V6 that is was 50ma higher current on that tube than was called for. . It exhibited the sound characteristics of this unit, don't remember if it smelled.

    My other reasoning is if it was a bad component it should react right on start up, not after being run for 15 minutes, which ironically seems to be when the power tubes reach temp.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    I guess the next logical step is to try different power tubes. If the problem still exists then it's time to send her in.

    I was just thinking outside the box with the smell test and looking for some discussion. Keep it coming.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    Quote Originally Posted by Msabot1 View Post
    Maybe a transformer fixing to take a dump? Happend to me,clue was the crackling noise you spoke of...they kind of smell at first and when they go it stinks bad...just a thought.
    Tranny case is stone cold. You could be right. This was brand new when I bought it. If it has 25 hours on it, I'd be surprised.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    I’ve seen transformers that contain wax to prevent hum from windings vibrating. The wax can melt if temps get hot enough inside which means something is causing the PS tranny to get that hot. If a wax filled transformer gets hot enough, it will leave traces like poo piles under it and the odor remains. But you say the trannys are not hot.
    Last edited by SCompRacer; 09-08-2013 at 12:43 PM.
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    While I've never had to use the smell test on audio components, I've used it on telcom circuit cards with pretty good success. It sounds to me like you've used it as far as it'll go and now it's time to change out the suspected culprit.
    My equipment sig felt inadequate and deleted itself.

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    Sniff, visual, temperature sensing with hands (no touching on ac parts, cables, wires, transformers, capacitors, tubes or transistors) is usually the first step I do with all electronics problem.

    But like everyone else have already said, I would just replace the offending toobs and see if it go away. If it doesn't, look for the crack in the tube sockets underneath or clean the sockets with electronics cleaner.

    If you do roll toobs often as you are, tube sockets could probably be lose or dirty or have a micro crack somewhere.

    If the other parts involved, you really need a meter and a schema to start looking for the offender.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone.

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    My guess would be that you have a bad tube in the mix somewhere and it's roasting a resistor beyond medium rare.

    Tom
    In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

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    Quote Originally Posted by treitz3 View Post
    My guess would be that you have a bad tube in the mix somewhere and it's roasting a resistor beyond medium rare.

    Tom
    This was my first thought as well. I think you are smelling the resistor, but a tube is causing it to "cook".
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    ^^+2^^

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    Ok, so I finally had some time to spend swapping in different power tubes on the offending channel. So far so good! Must be a bad tube out of the pair on the left side. Thanks for the help in troubleshooting. I sort of had a feeling it wasn't the gear.

    Now does anyone have a tube tester to test 6L6GC's to see which of the two is the bad one. I hate to figure it out in amp, as I don't want to do damage.

    Thanks

    H9

    P.s. The office rig sound fantastic!
    Last edited by heiney9; 09-14-2013 at 04:30 PM.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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    I thought this thread was going to be about panties. :/

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    Naa...not so lucky....glad it wasn't a trans...

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    Quote Originally Posted by heiney9 View Post
    Ok, so I finally had some time to spend swapping in different power tubes on the offending channel. So far so good! Must be a bad tube out of the pair on the left side. Thanks for the help in troubleshooting. I sort of had a feeling it wasn't the gear.

    Now does anyone have a tube tester to test 6L6GC's to see which of the two is the bad one. I hate to figure it out in amp, as I don't want to do damage.

    Thanks

    H9

    P.s. The office rig sound fantastic!
    Glad you got it figured out Brock. No "overdone" resistors though, huh? That's good news. My brother might have a tube tester that can test 6L6GC's. I don't remember for sure, I can ask him.
    Taken from a recent Audioholics reply regarding "Club Polk" and Polk speakers:

    "I'm yet to hear a Polk speaker that merits more than a sentence and 60 seconds discussion."

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    Quote Originally Posted by nikolas812 View Post
    I thought this thread was going to be about panties. :/
    Ya know.....you and I think a lot. Smell test ?? Last time I used that was in High School. Then I saw it was Brock who posted and figured he just had a smelly sock left behind the gear rack.
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    Quote Originally Posted by tonyb View Post
    Ya know.....you and I think a lot. Smell test ?? Last time I used that was in High School. Then I saw it was Brock who posted and figured he just had a smelly sock left behind the gear rack.
    I'm thinkin' you and Nik maybe has a wore out Sept 93 issue of Hustler....the S & S page....
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    Quote Originally Posted by headrott View Post
    Glad you got it figured out Brock. No "overdone" resistors though, huh? That's good news. My brother might have a tube tester that can test 6L6GC's. I don't remember for sure, I can ask him.
    The resistors look and smell fine. I shut it down both times as soon as I smelled that smell. I ran it yesterday for a couple hours with zero issues. It does have fuses so I;m not sure if it got real bad if the fuses would have eventually popped or not.

    Yeah, check with your brother, I just want to eliminate the bad one.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

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