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6550 tube issue - Super Bassman 300

Discussion in 'Amps and Cabs [BG]' started by rodl2005, Apr 14, 2014.

  1. During the 1st song of the last set the other night I got a distorted sound with a Hi pitched whistle noise. 😞 The Super Bassman Was still gutsy & loud. Asap I looked round back at the bias lights & one was orange. Indicating an issue but not a total fail - which I think the lights then go red -orange light means amp has it sussed & is addressing the problem -again, I think.
    By the next song it was sounding great again. 😎 The bias lights were all green again after that next song .
    After the set the lights were all green again too.
    Whaddya think?
    The amp doing what it's supposed to do. .. a bad tube so the amp adjusted itself? ?
    That tube is Probly on its way out etc etc. ..?
    Re buying a new 6550 or pair of. . So do I buy the same type of tube as what's in there or do I go for another, more highly regarded 6550 or pair ??
  2. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If it doesn't occur again, I wouldn't worry about it. It could have been an aberration within the bias circuit. It could be that your tube has an intermittent issue that is temperature related. There are a lot of welds within the tube and one could be loose, when the tube heats and the metal expands, the issue goes away.

    One test that you could do is start with the amp cold and see if the problem occurs. If not, give that tube a few light taps with a pencil or a piece of wood and see if anything happens. If the tube has an intermittent contact, the tapping might reveal it.

    There are plenty of options when it comes to tubes. In general, you pay for what you get. The better tubes can cost more. Get whatever you can afford.
  3. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    If it happens again, momentarily switch the amp to standby and back. If it's a glitch, that should reset it.

    How long have you had the amp, and specifically the set of 6550s?

    You don't have to be so ready to spend money. ;)
  4. Good points. Thanx guys. 👍👍
    I've had the amp a year and it's done about 25 gigs. The tubes are all stock-in it since I got it. (Except the V1 & V2 pre amp tubes- they're NOS GE5751's) It's 300w so has only really been pushed once.
    It did happen once about 6 months ago (I'd forgotten about that. I turned it to standby and noise kept going so I switched amp off, left a min, then switched back on & all was well) but has been perfect since.
    I ain't wanting to spend $$ but have been thinking about having a matched pair of 6550's on hand just in case.