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  1. #1
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    Default When a tube amp start loosing sound...

    As someone of you already know I'm owner of small hybrid Marshall amp, serie 8040 or Valvestate VS 40. This 40 Watt, 1x12, twin channel combo features an ECC83 (1 2AX7) valve in the Boost channel's pre-amp section for authentic valve distortion. Contour, Reverb and an Effects Loop make this amp equally effective at home, on stage or in the studio.I'm not sure 100% is there ECC83 or 12AX7... until now it worked fine but today I wished to spend some time playing axe after string replacing and until volume was up to "9 o'clock" all was fine...but when I turned volume up to "11 o'clock" after few power chords sound start to "bleeding" part of second or less :? , I though that maybe guitar-cable is failure but amp continued to produce sound except here and there start to loose sound like someone turned of very fast volume and back... :roll:
    I didn't never check condition of the tube inside amp 'cause former owner said that inside is new tube. I know that tube color changes from warm orange to a blue, or purple cast. Even if it still works fine, it's on it's last legs. Then it shall be changed, but this was easy visible at my former JCM900, 800 from back side... here nothing a man could to see!
    Did you had such "features" at your amp and what is your opinions? Is maybe possible that tube isn't no more so good in her place due to vibration, or ...? :shock:
    Thanks..
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  2. #2
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    Default

    Hey LF,

    I had a similar problem recently, with my Traynor, where I'd lose volume sporadically. Stop playing for a bit and everything was ok. I checked all the tubes and all seemed ok. But, after pulling all the tubes from their sockets and reinstalling, the problem had disappeared. I suspect I had a loose, or corroded pin connection on one of the output tubes.
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  3. #3
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    Quote Originally Posted by gpower
    Hey LF,

    I had a similar problem recently, with my Traynor, where I'd lose volume sporadically. Stop playing for a bit and everything was ok. I checked all the tubes and all seemed ok. But, after pulling all the tubes from their sockets and reinstalling, the problem had disappeared. I suspect I had a loose, or corroded pin connection on one of the output tubes.
    Hey dude, thank you dropped here your experience with this problem... I really appreciate each way of suggestion or intention to help, ... I would like to know approximately what could be problem before I decide to bring it to service. Big problem is that in my city isn't any of specialized amp service and I wouldn't like that someone is lurking inside and that in same time has no idea what is problem and how to fix... :?
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  4. #4
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    Default

    Today morning I opened amp with screwdriver in order to check condition of the tube. here is picture of it:

    and IMHO it's genuine tube that is shipped from factory and not possible to buy like spare element in the store in Germany or Austria? I know at least for 5 tube manufacturer but never heard that Marshall himself produced tubes :roll:
    I took out with rubber gloves tube, visual checked (no dark spot or crack), made image and put back in amp. There everything looks cool and good, no smoke or snuff...
    After that I tried again but now nothing noticed... I'm now a little confused :? shall I make replacement of ECC83; I saw that Electronic Harmonics's products are most popular... :?:
    Fender guitars - the best things for every man. After chicks, of course.

  5. #5
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    Default What is this?

    I found this one "help" on some forum about amps:

    Quote:
    Originally Posted by daggstar View Post
    i have a marshal valvestate amp model 8040 when it has been on for awhile it goes very quiet and then comes on for a second and then off for 30 or so , any ideas ??? could this be a valve problem ???
    When you're talking about 'going off' you've got to be more specific. Is the power light going off and on, or are you just losing sound?

    If you're merely losing volume, and your amp has an effects loop, a dirty return jack is most likely the problem.

    When the thing is quiet (exhibiting the symptom) plug an extra guitar cord into the RETURN jack, Now remove it. Repeat several times quickly. Likely as not this will bring full volume back. If it does, it means cleaning or replacing the jack. This is very common failure in guitar amps with an FX loop... especially if you don't usually use the loop jacks.

    Regards,
    Bill
    but I don't understand at all how "return jack" could be source of my problem? Honestly, I really don't use loop inlets, just standard guitar input... :roll:
    Fender guitars - the best things for every man. After chicks, of course.

  6. #6
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    Default

    Littlefloor -
    sorry to hear of your amp problem.

    1st, a 12ax7 is a type of ecc83. You can use ANY 12ax7 (or 12at7) - no problems!
    Electronic Harmonix is a good brand for a cheep(?) spare tube or for trial and
    error (testing) purposes. I have used their preamp (12ax7) tubes in the past
    and for the price, they were just fine. Marshall never made any tubes,
    they just put their name on it (that I know of).

    You may want to check all nuts that hold tight all the input/output jacks on the amp.
    I have seen a loose send jack on the effects loop cause that problem. Even
    though it was not in use, it is part of the signal chain and can short out if
    loose or 'bad'.

    I can not comment on the quote from the forum you posted. Worth a try
    though, as it seems easy (and Free!!)

    Post back & good luck!
    -tw

  7. #7
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    Default

    If the problem doesn't resurface LF, don't worry about it. That's exactly what happened with mine and why I suspect it was corrosion on one of the pins or in the socket. Pulling and reinstalling the tube just may have fixed it.
    Whether you think you can...or you can't...you're right!

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  8. #8
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    Default

    Dear tw001_tw & gpower,
    I really appreciate your time you reserved to make answers... I know that VS8040 isn't "monster engine" like his stronger brothers from JCM series but kids and me have fun playing through it... Funny side is that we never turned volume above 60-70% 'cause nothing noticeable could feel in next 30-40% remained of volume... and in this amp power in preamp isn't so high like in mentioned amps 50 and more watts, so tube shall last much longer, at last need replacement each 12-15 months, not each 6-8 months like by JCM series that is always "in action"...
    I think that is maybe good try to open amp and play some time in order to see how tube will behave..? :roll: Pulling out and back tube is simple process but I must to start abou' possible obtaining new tube EH, JJ, Sovtek or Tung-Sol 12AX7... :cry: Price isn't problem, just way of payment (credit cards)... damn.
    Fender guitars - the best things for every man. After chicks, of course.

  9. #9
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    Default

    Elvir, I know nothing about effects loop circuitry, so I can't comment on what you quoted above - maybe 145 Guy will find a gap in his wacky schedule to comment. Regarding your tube, you may be able to find some extremely good OLD tubes in your part of the world, since some of the better ones were originally manufactured much closer to you than to the US. Do you have any old-time Television or Radio repair shops around? Those guys often have massive piles of old tubes, and you might be able to find an old Seimens, (original pre-Tesla) JJ, Telefunken, Brimar, Bugle Boy, Phillips or even Mullard tube for a low price. You could use an ECC83, 12AX7, 7025 or CV4004 tube in that slot.

    If your amp is working properly after pulling and replacing the tube, it may have just been a dirty/oxidized pin, as gpower & special sauce has pointed out. But old tubes are cool, so you might want to poke around a bit.
    The Human Torch was denied a bank loan.

  10. #10
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    Default Thank you Tele

    @Tele savalas: thanks you stopped for a moment to share your idea. I'm not sure that thise valve could be possible to find in they old TV or similar gear 'cause many of them are devastated in last war and replaced later with IC & transistor powered gears... if nothing help, then I shall make trip to Sarajevo or Zagreb in Croatia. That's life of us, artists 8)
    Thank you for information about other designation for ECC83... if I meet some of them.
    Maybe 145 Guy will say some new unknown info about this "amp feature" in meantime..? In the case he spot this message..?
    Fender guitars - the best things for every man. After chicks, of course.

 

 

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