My 1st tube horror

brianle
brianle Posts: 572
edited April 2013 in 2 Channel Audio
Bought a 2nd hand Cayin a100-t integrated amp. The seller listed it as 9/10 but it's actually a 7/10 on agon's rating. In addition, he shipped with the tubes and cage installed which caused some additional scratches during shipping. Then I replaced the stock output tubes some NOS winged c 6550, the moment I turned on the amp, there was flare from one of the tubes which seemed to blow out one channel. :redface:
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  • george daniel
    george daniel Posts: 12,096
    edited April 2013
    and,, was it the tube or bias resistor or?
    JC approves....he told me so. (F-1 nut)
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  • cstmar01
    cstmar01 Posts: 4,424
    edited April 2013
    does the amp have any fuse protection? hopefully nothing too bad happened as sometimes tubes can go.

    And I'm sorry but its stupid to ship with the tubes installed. I got my VTL's the same way and wasn't too happy as it can cause issues. I didn't have any but I've seen some other things like this happen. One just recently was on a VTL pre amp that was shipped with the tubes and the buyer got it with them rolling around and the scale wasn't followed either.
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  • brianle
    brianle Posts: 572
    edited April 2013
    no fuse protection so I'll have to bring it to a shop for evaluation/repair
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  • madmax
    madmax Posts: 12,434
    edited April 2013
    That thing has got to have a fuse, are you sure it doesn't? In my Jolida the first time a fuse blew I saw the light from the fuse blowing and thought it was from a tube. Did the original tubes work? Did you re-bias the amp when you changed the tubes?
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
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  • brianle
    brianle Posts: 572
    edited April 2013
    If it has fuse protection, then it must be inside the amp. I haven't tried to open it yet as cayin noted no user serviceable inside. The original tubes worked. The right channel went dead the moment I turned on the amp so I didn't even have a chance to bias.
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  • thsmith
    thsmith Posts: 6,082
    edited April 2013
    Chances are you had a bad tube that took out the bias resistor.

    A multimeter will very the resistor and a tube tester will verify tubes function
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  • madmax
    madmax Posts: 12,434
    edited April 2013
    When I change tubes I normally set the bias to its lowest voltage, then replace the tubes, then dial it up to what it should be. I'm not sure how long you can leave the bias really high on a tube before you have problems but with this method it never happens. Certainly you should have some amount of time before the tube goes bad. I tend to agree with the above that maybe you got a bad tube. Everyone as far as I know always fuses the power because they don't want a bad tube to take out a bunch of componets.
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
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  • brianle
    brianle Posts: 572
    edited April 2013
    Thanks, madmax. Yeah, I forgot turn the bias to the lowest point before I put in the new tubes. The flare appeared the moment I turned on the amp. I will open up the amp tonight to see if there is any fuse inside.
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  • organ
    organ Posts: 4,969
    edited April 2013
    madmax wrote: »
    When I change tubes I normally set the bias to its lowest voltage, then replace the tubes, then dial it up to what it should be. I'm not sure how long you can leave the bias really high on a tube before you have problems but with this method it never happens. Certainly you should have some amount of time before the tube goes bad. I tend to agree with the above that maybe you got a bad tube. Everyone as far as I know always fuses the power because they don't want a bad tube to take out a bunch of componets.

    That's what I do as well. And I do the final set around 3am when the output voltage in my house is at it's highest between 122 and 124. Wall voltage affects the bias.
    When I got my first tube amp, I set the bias about 20 secs after power up. In less than a minute, the plate was glowing cherry red and I immediately turned it off. Any longer and it probably would have taken out the output transformers.

    Brian,
    Sorry to hear that. Hopefully it just took out a resistor which shouldn't take long and won't cost much to repair.
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  • brianle
    brianle Posts: 572
    edited April 2013
    Thanks, organ!
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  • Goldenboy72206
    Goldenboy72206 Posts: 126
    edited April 2013
    that sucks
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  • heiney9
    heiney9 Posts: 25,204
    edited April 2013
    madmax wrote: »
    When I change tubes I normally set the bias to its lowest voltage, then replace the tubes, then dial it up to what it should be. I'm not sure how long you can leave the bias really high on a tube before you have problems but with this method it never happens. Certainly you should have some amount of time before the tube goes bad. I tend to agree with the above that maybe you got a bad tube. Everyone as far as I know always fuses the power because they don't want a bad tube to take out a bunch of componets.

    This is good practice! In my rookie days I swapped power tubes w/o checking the bias. One of the 4 tubes started hissing and popping after about 30 minutes. After this happened I decided to check bias and it was high on that tube. Since then I do the above.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • brianle
    brianle Posts: 572
    edited April 2013
    Yup, I made 2 rookie mistakes:

    Bought untested tubes
    Didn't set the bias to its lowest voltage when plugging in the new power tubes
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  • madmax
    madmax Posts: 12,434
    edited April 2013
    I forgot to mention one thing in my method of biasing. I start at the minimum bias -then I let warm up for about 10 minutes then bring up to 50%. After about half an hour I bring up to about 75%. At the end of an hour I bring up to full minus a few miliamps. Later on I check to see if they are still at that value and if not I tweak them. Also, the next few times I power up cold I watch to make sure they are still set correctly. If I see the bias staying higher for more than a few minutes before being completely warmed up I tweak them back.-
    Vinyl, the final frontier...

    Avantgarde horns, 300b tubes, thats the kinda crap I want... :D
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  • brianle
    brianle Posts: 572
    edited April 2013
    20130416_163659.jpg


    back in business after replacing the fuses and voltage regulator :)
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  • zingo
    zingo Posts: 11,258
    edited April 2013
    Congrats! I hope it didn't cost you too much; any financial help from the seller since they shipped it in not ideal conditions?
    Jake
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  • brianle
    brianle Posts: 572
    edited April 2013
    $144. My tube repair guy said the amp was modded with incorrect fuses which didn't work when the bad tube was installed. As a result, the blown tube also took out a couple of resistors and the voltage regulator. No help from the seller.

    cayin.jpg
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  • zingo
    zingo Posts: 11,258
    edited April 2013
    Bum seller, but not too bad on the repair cost, and you have a working amp now most importantly!
    Jake
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  • brianle
    brianle Posts: 572
    edited April 2013
    Yup. He had a couple good sale feedbacks so I thought I would take a chance with him ...
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  • ViperZ
    ViperZ Posts: 2,046
    edited April 2013
    Hate it when someone sticks bigger fuses into electronics without thinking of what might happen when failure occurs.
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  • cnh
    cnh Posts: 13,284
    edited April 2013
    Good to hear you have that back up and running. She's a "Beauty" for sure!

    What kind of power does that put out per channel?

    cnh
    Currently orbiting Bowie's Blackstar.!

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  • polkfarmboy
    polkfarmboy Posts: 5,703
    edited April 2013
    Nice happy ending to your horror story, now you can just kick back,relax and enjoy
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  • brianle
    brianle Posts: 572
    edited April 2013
    cnh wrote: »
    Good to hear you have that back up and running. She's a "Beauty" for sure!

    What kind of power does that put out per channel?

    cnh

    supposed to be 100w/channel in ultra-linear and half in triode mode
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  • brianle
    brianle Posts: 572
    edited April 2013
    polkfarmboy wrote: »
    Nice happy ending to your horror story, now you can just kick back,relax and enjoy

    thanks! :cheesygrin:
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