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YBA200 trouble; tube amp guys, please help!

Discussion in 'Amps and Cabs [BG]' started by SherpaKahn, Feb 28, 2008.

  1. SherpaKahn


    Dec 1, 2005
    Bronx, NYC
    A while back one of the 6550s in my Traynor YBA200 went out with a spectacular flash and I ran it with two tubes pulled with a 4-ohm speaker on the 8-ohm setting for a while. I just retubed it with JJ KT88s a week ago and although I like the way it sounds, after 5 on the gain and 5 on the master, it just loses it; nasty, hairy distortion cuts in and out intermittently, but always cuts in on the attack of the note. There's a 5751 in the preamp, so it's not the usual problematic YBA200 distortion; it's definitely related to the power section.

    I've heard that the cathode bias on the YBA200 tends to not quite match up too well with some KT88s, so maybe this is crossover distortion, but I opened up the chassis to look around and pin 8 of the socket for V6 is scorched, as well as the both ends of resistor 64 (R64). The traces in that area are fine, and once I can get a multimeter I'll test R64 to make sure its value is still correct, but in the meantime, could anybody check out the schematic and offer any advice as to what could be causing this, if I may have a bad screen resistor? Any help would be appreciated.

    Here is the service manual: http://www.traynoramps.com/downloads/servman/smyba200.pdf

    R64 is at intersection L9 on page 1 of 2 of the schematic (1W, 10 ohms)

    And here's an example of what it sounds like:


    It's really too bad, because I was getting some great headroom out of this and I may need some real volume out of this amp pretty soon. Also, I am very aware of the dangers of opening up a tube amp, and am being duly cautious.
  2. SherpaKahn


    Dec 1, 2005
    Bronx, NYC
    Tomorrow I buy a multimeter. Do the bump!
  3. Dunno- all I do know is I've had GREAT experience w/ JJ tubes in the past-THO with KT77's not 88's. So ....... BUMP again.
  4. Take the amp to a tech. You are risking your life here. Do you not consider your life to be worth the couple of hundred bucks the repair may cost? Sounds to me like your bias circuitry is on the fritz. You do not have the skills to repair this amp.

  5. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    Tube failure can cause damage to bias/balancing circuitry. Get it to a tech. There's got to be plenty in NYC.
  6. RevGroove

    RevGroove Commercial User

    Jul 21, 2002
    Burlington ON Canada
    Manager, Account Services: Long & McQuade Ltd. (Burlington); MTD Kingston Basses International Emerging Artist; Bartolini Electronics Emerging Artist
    Paul and Ben are right, get the amp into a tech. Better to be safe than sorry!

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