Diagnosis Request: JCM 800/2210

Discussion in 'The Workbench' started by NewReligion, Jul 28, 2010.

  1. NewReligion

    NewReligion Well-Known Member VIP Member

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    This is a 1989 JCM 800 2210. It is starting to Squeal, Fart, Pop and Crackle when set up as it always has been over the last 20 years. My trouble shooting consisted of changing out Power tubes and biased to 70% disipation in addition to 5 new Pre-amp tubes. Different Guitars/Cabs/Cables. On-Board Reverb on off. The problem persists, "Until I turn down the Gain Knob below 7.5 or less. In addition the tone goes to hell at this low level and sounds even worse at higher settings. When turning the Gain up above 7.5 it has a modulation/phase type effect to the gain structure in addition to sounding as if it is about to blow and must be shut down/backed off immediately.

    I have owned many of the 2210/2205 models and have always ran them on the boost side with the Volume and Gain maxed at 10 then adjust the over all volume with the master volume or Input/Output controls of a processer in the loop.

    I assumed that with all of the talent here at the forum one or all of the Technical Genius's would be able to point a finger in the right direction if not just out right say, yeah it is x,y and or z. Thank you in advance.

    David Hopkins. :jam:
     
  2. jcmjmp

    jcmjmp Well-Known Member

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    Clean and re-tension tube sockets. See if that solves the pop/crackle noises.

    Once you fix that, we can move on to the next problem.
     
  3. NewReligion

    NewReligion Well-Known Member VIP Member

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    Thanks JCMJMP.
     
    Last edited: Jul 28, 2010
  4. Marshall Mann

    Marshall Mann Well-Known Member

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    Hey Dave,

    To re-tension, use a clean jewelers screwdriver or small steel nail (etc) to make the contact points as tight as possible against the pins on the tube. Use caution not to damage the socket.

    This sounds like a tube / socket problem to me.
     
  5. NewReligion

    NewReligion Well-Known Member VIP Member

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    Really? Loose tube sockets. Just close the socket contacts? I will work on it when I can. Also it seems be becoming "very" saturated with distortion when the gain is pushed beyond 7.5

    Thanks for the tips.

    DCH
     
  6. jcmjmp

    jcmjmp Well-Known Member

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    Yes, you just close the contacts closer together so that they fit nice and snug on the tube pins.
     
  7. Marshall Mann

    Marshall Mann Well-Known Member

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    Yes. As JCM put it, it's where you start.

    The contact points in the socket that actually touch the pins are very small. The tubes should be snug in the socket. I have had bad contacts cause problems like this more than once.
     
  8. NewReligion

    NewReligion Well-Known Member VIP Member

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    Will do. Thank you Gentlemen.

    DCH
     
  9. Lane Sparber

    Lane Sparber Well-Known Member VIP Member

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    I'd simply like to add this to the already great advice here:

    BE SURE YOUR FILTER CAPS ARE DRAINED BEFORE RE-TENSIONING THE TUBE SOCKETS!

    If those caps are not drained and you use a metal implement to re-tension the sockets, all you need to do (while working on certain pins) is to brush the chassis and you complete an HT circuit - with your body. Beware especially of pin 3 on any power tube. Just putting it out there for "safety first's" sake!

    Cheers!

    -Lane
     
  10. TwinACStacks

    TwinACStacks New Member

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    :) You mean Pin 3 counting counterclockwise from the key slot for the center guidepin? Like THIS ONE right here?


    AAAAAAAAAAAAAAAAAAAAAAAAAA.....
     
  11. Lane Sparber

    Lane Sparber Well-Known Member VIP Member

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    Oh silly me...I forgot to mention that in Twin's case, the amp should ALWAYS be fully powered up for ANY adjustments or modifications...especially changing filter caps. This ONLY applies to Twin. ONLY for him. :rofl::rofl::rofl::rofl::rofl::rofl:

    -Lane

    DISCLAIMER FOR NOVICES: ALL amps should be powered down and the filter caps drained for ANY work performed on an amp...unless the amp NEEDS to be on for the work performed. These amps contain LETHAL voltages that can KILL you, so don't take my above suggestion seriously...EVER. Unless you're Twin.
     
  12. NewReligion

    NewReligion Well-Known Member VIP Member

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    LOL. :) Thanks, another reason to want to be just like Twin.
     
  13. TwinACStacks

    TwinACStacks New Member

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    :D Jeez David, You just saved me from Shaving my head, setting my amps on fire, and standing in front of them, because I wanted to be a Guitar God just Like You.

    (I Truly enjoy your music, Regardless of the Cover Art....)

    :lol::lol: TWIN
     
  14. NewReligion

    NewReligion Well-Known Member VIP Member

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    :) Don't shave your head unless you can pull it off. A bald werecow may have trouble getting laid. Also it attracts the "Really Bad" girls who dig Alpha males. You know, the naughty ones who will do anything just to be with you.

    Back to the matter at hand. Tightened the tensioners, no change. Bias is unstable and will run from Output Socket 1 - 40% to Output Socket 4 - 90% DANGER! DANGER! DANGER!

    No matter how low I set the Bias the last Output tube will Drift Far Too High. I tried many different tubes in all different positions and documented the results in relation to the labeled tubes. Same results, all negative. Guess I can Send it in for repair or move it to an individual I know that wants it so bad even though it is in bad shape. I suspect OT maybe?

    Any and all thoughts are welcome. Thanks.

    David :band:
     
  15. RickyLee

    RickyLee Well-Known Member VIP Member

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    So if I am understanding this correctly, 3 of your 4 output valve positions function properly: V6, V7 & V8. Position V9 has an escalating/runaway current no matter what tube is put in this socket?

    V8's idle current stays where you set it, but it's mate V9's idle current keeps climbing higher?

    Have you tried running it with only two power tubes installed - 50 watt mode with amp set to half the speaker load of course - with a tube in V9?
     
  16. NewReligion

    NewReligion Well-Known Member VIP Member

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    Yes I switched to 8 ohms and ran many dual tube sets in V6/V9 and then
    V7/V8. I still get the "Over Saturated" squealing feedback when I turn the Gain and Preamp Volumes up past 8, no matter where the Master volume is set.

    The Plate Voltage also has jumped from 458V in Oct 2009 to 476V as of today. The GT EL34's run V6=26mA / V7=20mA / V8=38mA / V9=50+mA.

    As a younger man I recall a JCM 900 2500 doing the exact same thing just before most of the board fried. Same saturated high squeal. I can turn down the gain and preamp volume to eliminate the squeal but it effects the tone by adding or subtracting treble.

    In addition, if the effects loop is used, the volume is no where near what it should be. However the onboard reverb still works. :hmm:
     
  17. Lane Sparber

    Lane Sparber Well-Known Member VIP Member

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    There are several things that could cause these issues, and because of that I'd say these repairs are best left to a tech, David. If you're not comfortable with doing this work yourself (or around high voltages), it's time to get it serviced by a pro, because the amp would need to be fully powered up for a lot of this diagnostic work. Just my $0.02 here, but I feel it would be madness to try to perform a repair of this order over the internet.

    Good luck!

    -Lane
     
  18. NewReligion

    NewReligion Well-Known Member VIP Member

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    I Agree Lane. Thank you all very much for the outstanding support. I have done all I can do.

    David :cheers:
     
  19. jcmjmp

    jcmjmp Well-Known Member

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    I would check the input grid resistors.
    Also, check that the bias voltage on pin5 is stable with no tubes in.
     
  20. jalexquijano

    jalexquijano Member

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    i also have a JCM 800 2205 which is producing a high pitch squeal if i dial the gain pot from 7.5 to 10? What could be the cause?
     

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