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psarkissian

Service Engineer Moderator
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Posts posted by psarkissian

  1. innonovine: "JJ's have a tendency to damage certain parts of the processor board--- Which parts, exactly, and why? Citations needed"---

     

    Unless you're an authorized service tech and signed an NDA (non-disclosure form),... I can't get into that

    any deeper than I already have. Sorry.

     

    Don't use JJ's, use the specified EH's,... the JJ's will go outside the linear region of the characteristic curve too easily,

    and that will create problems further downstream, and stress the circuits.

     

    And I would have to have give an online course on tube amps for the uninitiated.

     

    Right, there is no voodoo,...  just knowing what the technology is and where the limits are. 

    Don't go beyond the limits,... physics is unforgiving in that way.

  2. Charlie on the spot. Correct.

     

    ColonelForbin,.. the Shuriken guitars would have to do it the way Charlie says it.

    I know, I've done it. 

     

    As for 59 vs 69, the board is the same, It's the program that's different.  

     

    No "Zap",... the controls stay the same.

     

  3. radatats is right,...

    "... while they MAY be compatible, they may also be different. apparently original 6CA7's were identical to EL-3s but today's 6CA7 version is a beam tetrode whereas the EL-34 is a pentode"----

     

    The power tubes that come stock with these are "pentodes", that's how the circuitry is designed.

    Don't mod these amps, use the specified tubes, you will have less problems.

    • Upvote 1
  4. Melted glass is usually a result of 'red plating'. It can get so hot,

    that the glass will melt and pucker until it cracks and loses vacuum.

    Seen that more times than I would like to. 

     

    Depending on how much gigging you do, tubes ought to be changed

    out every 12-18 months. If you're a recreational player and don't gig

    or record much, you can get away with 2 to 2-1/2 years.

     

    But, yes,... I've seen tubes in amps in general (at other places I've worked)

    last two weeks in one amp and 5-years in another. Partly the amp,

    partly the tube.

     

     

    "What precautions can we take to ensure that our amps don't wind up on your bench?"--- Don't try to modify

    it, use specified tubes, change out tubes on a regular basis. It's your friend, your tools, take care of your tools.

    And used Line 6 authorized service centers, as they will have access to proper service info,... at least while your

    warranty is good.

     

    And by all means,.... please DON"T go inside these amps yourself, the shock hazard is too great. Don't want read

    about how someone got zapped messing with a tube amp. This is dangerous,... I'm a tube geek, I was trained to

    do this, been dealing with tube amps and solid state amps since the 1970's. And been zapped enough to know better.

     

    • Upvote 1
  5. Yes. Red plating isn't the only way to damage the unit.

     

    To explain that further gets  into aspects of the circuit

    that I can't get into. It all goes to the characteristic curves

    of the tubes.

     

    JJ's have a tendency to damage certain parts of the processor board, 

    Mesa's tend to "red plate", and Groove tubes tend to do a host of other

    things.

     

    Part of it is that it's a Bogner hot rod, part of it is that there are multiple

    gain topologies that are on this amp that can be engaged, and so messing

    with it is not a good thing to do.

    • Upvote 1
  6. -Red Plating, for one. Too much current going through the plate element.

     

    -Biasing other brand tubes to the same spec as the EH's would not be a

    good idea.

     

    -Circuit is designed to operate in the linear region of the "characteristic

    curves" of the tube. Other brand's linear regions don't always match curve-to-curve.

    If you go non-linear too soon, distortions and other related problems occur,...

    stuff starts to get damaged or blown. Bias and gain stages play into this.

     

    -And with a hybrid amp like this, one of the things that typically goes, are a

    couple components on the processor board.

     

    -There are multiple gain structures on the amp board, using tubes with afore

    mentioned aspects also play a part in what can get damaged.

     

     

    Other aspects I won't go into because it's a tube engineering thing that most

    people won't get (except tube geeks like me),... and because there are also

    aspects I can't get into because it's proprietary.

     

    Pushing a hot rod to the edge is not a good idea here. It's already a hot rod,

    and a hybrid one at that.

    • Upvote 1
  7. "It was like a crackle pop sound"--- electronic,... a few different possibilities.

    An authorized service center could narrow it down, nip it in the bud, and check 

    the set-up,... all at once.

     

    JTV's are all set-up and checked out before they leave the distribution center.

    Cross country travel, climate change from region-to-region can have an affect

    on the set-up. The set-up may need to be dialed-in a smidgeon.

  8. Sounds like a set-up issue, maybe a result of fret buzz getting

    processed with the rest of the audio.

     

    High-E slip on a 69 was with an earlier run, the fret dress specs were

    adjusted and no problem since. That newer fret dress spec was applied

    to the 69S later on, so High-E slip hasn't been an issue on the 69S.

    Set-up may be an issue here as well, may need to be dialed-in a smidgeon.

  9. Don't mess with it yourself, have an authorized Line 6 service center do it.

    They will have access to service info and the know-how to use it. This is not

    our grandfather's Marshal stack, it's a hybrid. If you don't know where the

    trim pots go, then don't go there. Leave to the experienced tech who's worked

    on these. I see too many failed attempts come across my bench.

     

    And using info from a Spider Valve link won't apply to the DT series. Different

    beast, different gain structure,... not to be taken lightly. Nor is its supply voltage.

    There are high voltage supply lines that should not be tampered with. Leave it

    to the service center with the knowledge and the service info access.

     

    Besides, if you get zapped, it hurts.

    • Upvote 1
  10. "You almost make it sound as though the EH EL34 pair I ordered from MF

    would not meet the same requirements that the OEM tubes meet"---

     

    I guess the operative word is "almost".

    EH matched pairs should have a spec marked on it (Plate Current and Transconductance).

    If it's EH and they're matched they would fine. From MF or whoever has them is fine.

  11. DT series likes EH's, never seen any China tubes in them from the factory.

     

    Spider Valve uses 12AX7B (China) for preamps and Sovtek 5881WXT,...

    should use the WXT versions especially a must if the tube retainers are

    the "bear trap" type.

     

    Alchemist amps are another story altogether and specified tubes are even

    more crucial and specific.

     

    These are hybrid amps with some complex gain loops, so using specified

    tubes is a must.

     

    • Upvote 1
  12. Flavors never mattered to me. some people are into that.

     

    What we get from EH (matched pairs) has been extra tested saying that

    they passed our requirements. They also have the crucial Plate Current

    and Transconductance marked on them. What flavor they are, I don't

    recall, they are what they are, fitted spec'ed for this group of amps. They

    all meet the spec.

     

    Mike Matthews of EH is an old school circuit geek (like me), so we always have

    much to talk about when I see him at trade shows. As well as my trade show

    chats with Aspen Pittman of Groove Tubes.

     

    Tony, boo boo? Not really.

    Sovtek, EH,...  same factory, and the factory is owned by EH.

    EH marked tubes go through extra scrutiny.

    • Upvote 1
  13. Because of the way Bogner designs the tube portions of these amps,

    and that this is a hybrid and not the usual bill-of-fare tube amp, you should

    re-tube using the specified EH from Electro-Harmonix tubes.

     

    You can't use the EH bias spec on other tubes. The spec is dialed in for

    the EH's.

     

    All too often these come across our bench for no other reason than having

    non-specified tube inside (JJ's, Mesa, Groove Tube), using the DT amp

    specified bias. That does not work.

     

    They (JJ's, Mesa, Groove Tube) would have to be bias slightly different,

    because the characteristic curves from one to the other are not exact. That

    little of difference, makes all the difference. I've seen too many blown amps

    come across my bench just because of that. It's a hybrid and a hot rod,...

    best don't mess with it.

     

    Stick with the specified EH's. 

    • Upvote 1
  14. Have you checked the Line 6 Knowledge Base?

    I gave a couple documents to be put up there last year,

    regarding JTV's, forgot what it was.

     

    The set-up isn't always as routine as you might think, given

    the interactions in Model mode. The processor will try to deal

    with fret buzz or warbling, as if it were part of the signal.

     

    And there's probably something in our set-up doc that's

    not meant for public consumption, that might factor into it.

    Though I don't know what that would be off-hand.

     

     

  15. Clay, et al- ... and remember, piezos are sensitive to impact shocks
    that can damage them, so be careful when dealing with them.

    Pluncking? Probably fret buzz or the nut slots need to be cleaned and de-burred.

    fr0sty- set-up on a JTV can be tricky because of the Model processing.
    this isn't your everyday kitty-cat, it's a tiger and has to be cuddled under
    the chin a little differently. It's not our father's archtop hollow body with
    passive electronics. The fact that pick-up height can affect Modeling
    (ie- warbling) is a perfect example of that. I get a few back from those
    who attempt and fail at an adequate set-up.

    stevekc- thank you for the kind words. Quality time indeed, I didn't want
    to part with it. Nice 59.

  16. Ghost Notes (aka- hollowing or whistling) is typically a result of set-up,

    either neck relief or intonation, or both. Most often it's intonation.

     

    Warbling is typically a result of the set-up, usually relates to pick-up

    height (most often, set too close to the strings). The magnet pulls on the

    string causing a warbling effect.

     

    http://line6.com/find/service_center/    for looking for a service center.

  17. Make sure it's the VDI cable and not everyday CAT5.

    VDI has the XLR casing. You need that so that the connector

    doesn't wiggle and cause intermittent contacts.

     

    Seen a number of connectors in the past with both old Variax

    and JTV, where someone used the cheaper standard CAT5

    Ethernet without the XLR casing. It resulted in bent pins, intermittent

    contacts and Volt transients that damaged the electronics.

     

    Always use the VDI version of the cable, and not the everyday CAT5

    Ethernet stuff,... please.

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