powering up without tubes?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Badbirdie, Feb 29, 2008.

  1. Badbirdie

    Badbirdie Member

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    As I was biasing my tube amp I accidentaly turned the standbyswitch from standby to on without the powertubes installed. Is this bad for the amp? I turned it back of right away. When I later tried to put the tubes in their sockets, there was a blue flash, and the fuse blew. Did I harm the amp, or can I just drain the filter caps and then install the tubes with fresh fuses?
     
  2. rockon1

    rockon1 Member

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    As far as I know theres no harm in powering up the amp without tubes in. In fact its often used to determine if you have a bad tube when an amp blows a fuse. (pull the tubes and power it up if the new fuse holds its probably a bad tube) Cant imagine why the fuse blew when you tried to put the tubes back in unless one went in the wrong way because of a poor keyway. (Ive had tubes with such crappy keyways I could get them to go in the wrong way!) Perhaps someone will come along with an explanation that Im not aware of. Bob
     
  3. 5E3

    5E3 Member

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    I don't think there is any harm.

    For an amp kit I built the instructions were to power up without tubes and take some voltage readings, prior to installing the tubes for the final test.
     
  4. stebnera

    stebnera Member

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    There's no harm turning the power on to an amp w/o the power tubes installed. If you saw a blue spark and blew a fuse, something else is wrong. It had nothing to do with turning the power on w/o power tubes installed.

    My guess is either you put the power tube in incorrectly, as was already suggested, or one of your tubes was bad. Also, if you were turning the bias pot when you turned the amp on w/o the power tubes in, you could have also set the bias current higher than the tubes can handle. Then when you installed the tubes, one of them red-plated and blew a fuse. I'm not sure what bias-setting procedure you were using.
     
  5. gtrplr71

    gtrplr71 Supporting Member

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    interesting thread not to hijack but does an amp need to be in standby or on mode when biasing?
     
  6. rockon1

    rockon1 Member

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    Has to be on. Bob
     
  7. mark norwine

    mark norwine Member

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  8. V846

    V846 Member

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    just be sure the filter caps are are rated high enough to withstand the increased voltage without the tubes installed..underrated caps aren't gonna like stress . what amp is it?
     

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