EL34 100/100 Power Tube Issue

Discussion in 'The Workbench' started by Panacea151, Nov 13, 2019.

  1. Panacea151

    Panacea151 New Member

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    First time posting. I have an EL34 100/100 with an odd issue, I guess. I tried searching the forum, but could not find anything that matched my issue.

    Tonight while playing, I noticed a distinct difference in tone coming from my speaker cabinets. Upon closer inspection, two of the tubes in the Channel A section were not glowing, but the other two were.

    There was no cracking nor popping or any other indication there was an issue. The tubes were replaced (TAD EL34s) and rebiased about a year ago.

    Any insight would be certainly appreciated.

    Thanks!

    Michael
     
  2. South Park

    South Park Well-Known Member

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    Check heater voltage and wireing
     
  3. Panacea151

    Panacea151 New Member

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    Thank you. I decided to pull the amp out of my rack and swap the front two tubes that were not glowing with the back two, just to see what happened.

    Now, all 4 tubes glow again, but there is a definite almost 60 cycle hum sound. If I tap one of the power tubes that was previously not glowing, it stops for a second. I guess I didn't notice it because I was playing.

    So now the question is, if I have a bad tube in this quartet, is it possible that when he stopped glowing, he took his push/pull buddy with him?

    Noting is red-plating or acting strange at all. But now that I am not playing, you can definitely hear a hum that goes away for a second if you tap the tube.
     
  4. South Park

    South Park Well-Known Member

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    Try cleaning the tube sockets you might have a bad contact
     
  5. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    As the heater wiring is in parallel then other than one or other of the tubes has an internal poor connection then a dry joint or two must be the problem, though it is unusual for two tubes to give the same problem at the same time but never say never.

    Other than if you are capable of doing the repairs your self, dont forget that you will need to appropriate kit do do this job properly, then take it to a good qualified Tech to do it for you.

    Tube amps in the wrong hands can be fatal.
     
    SkyMonkey and Jon C like this.
  6. Panacea151

    Panacea151 New Member

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    Thank you for the responses. The thing had the stock tubes in there since 1997 with no issues. I just had the thing retubed last year as a matter of maintenance.

    I'll take the bottom off today and see if any of the tell-tales of dry sockets are present and clean the tube sockets.

    Really strange that all of this appeared out of nowhere, but at 22 years old, it's probably time to get a good look at everything.

    Is it better to use a solder sucker in a dry joint, or just re-flow what's there?

    Thanks again for everyone's assistance, it is certainly appreciated.
     
  7. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    The best way to re-solder any joint at all is to first take off the old solder, so yeas use a solder sucker.
    The pins of the tube bases should be wire wrapped so the cable will stay put.

    Something like this will never give you any warning, so nothing unusual there.

    Be very careful when you look on the underside of the chassis as the main smoothing caps will still hold there charge long after the amp has been turned off.

    Not many of us after 22 years can say we need no attention, i for one can say i did and glad i did lol.
     
  8. Panacea151

    Panacea151 New Member

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    Thanks, Ken. I'll discharge the caps before I get started.

    Depending on what I find and how easy it is to get to, I may send it into my tech for the solder repair and a cap job, anyway. The caps are probably the next thing that will give me issues.

    I appreciate your help.
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    "not glowing" Give more details?
    Are you saying that one side of the amp has no filament? Or what?
     
  10. Panacea151

    Panacea151 New Member

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    The channel A tube quartet had two tubes (the front two, when looking at the amp head-on) that were not glowing and cold. The back two exhibited normal operation and there was still operation from channel A.

    Hope this helps, if not, please feel free to redirect me.

    Thanks for the reply,

    Michael
     
  11. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    You need to open the amp and check for a possible broken circuit track, broken solder connection etc...
    But you should not play the amp until the problem is fixed.
     
  12. Panacea151

    Panacea151 New Member

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    Thanks for your response. I'll be inspecting it shortly. I have a backup SS power amp to get me through while this one is down.
     
  13. Panacea151

    Panacea151 New Member

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    After scouring the board for gray joints, cracked joints, any signs of carbon, noticable signs of board damage, I am not finding anything.

    This must be a tube socket issue.

    Relying on the experts here, is there a preferred cleaning method, or is it just better to put new sockets in it?
     
  14. Jon C

    Jon C Well-Known Member

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    DeOxit G100 ……Gold Formula, No Solvent ……
    AMS buys it by the Case !!
     
  15. Panacea151

    Panacea151 New Member

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    Thanks! Ordering it right after this post.
     
  16. Seanxk

    Seanxk Active Member

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    Valves out, cap's discharged, mains off etc.
    I have a dedicated piece of wire fixed to a wooden handle, the wire is the same diameter as a valve pin so checking each pin hole will let you know if one is not grabbing.

    Some valve bases wobble quite a bit, this can sometimes break the wire earth connection via the valve base screw.
     
  17. Panacea151

    Panacea151 New Member

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    We use the same thing in the automotive industry to check terminal tension, that is an excellent idea, thanks!
     
  18. Panacea151

    Panacea151 New Member

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    Found a few questionable terminals, got them tightened up. Cleaned the terminals.

    Fired it up, and hum still there. Suspicious tube that shuts up momentarily when tapped, was placed in another location. Hum continued, but tapping the tube shuts it up. It does not seem to matter where that tube is at, it hums and will quiet momentarily after being tapped.

    I guess I have a bum tube. I'll probably put Svetlanas back in it and hope for the best. My experience with TADs in this amp hasn't been stellar.
     
  19. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    A tube socket issue would not make both tubes fail at the same time.
     
  20. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Re-solder all the connections.
    A bad solder connection may not have any visible signs.
     

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