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Ampeg Question - Re. Bias lights

Discussion in 'Amps and Cabs [BG]' started by jimmykebab, Sep 27, 2008.

  1. jimmykebab


    Feb 12, 2008

    Thanks to TalkBass members I got my USA Ampeg converted to UK 240v, so THANK YOU!

    I have a new question, my amp is playing up been used for about 20 gigs and the bias lights are both showing red and green, the manual says this is a tube issue which should be checked out by a pro, I know all the discharging info, but how do I identify which tubes are not working??? Any other relevant info would also be greatly appreciated.... Thanks,

  2. jimmykebab


    Feb 12, 2008
    Any ideas :(
  3. Did you reset the bias or have it checked after you changed the voltage taps?? Every time you make a significant change to an amp like this the bias HAS to be adjusted for optimum performance. Look ate the anodes (plates) of the output tubes. If any have glowing red spots the bias is set too low. This is not the heater but on the anodes.

  4. fatgoogle


    Jun 15, 2008
    not to highjack this thread but was it difficult to get the voltage changed did you take it to a tec or do it yourself.
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The bias lights are not THAT reliable...........

    I assume this is at idle, i.e. powered up ready to play, but no signal input. In that case the bias could be wrong, or a tube might be a problem.

    BOTH sets of lights at once suggests bias set wrong more than a tube, unless two failed at same time in more-or-less the same way.

    You can set it per manual and lights, or take it to a tech for a proper job using a meter etc.
  6. jimmykebab


    Feb 12, 2008
    Cheers guys.

    JT, yeah the amp is idle, if I sweep the bias I go from jumping between green and red, just red and green and red at the same time... A few gigs before this was all good, and I'm sure it was fine the day before I noticed the fault, could be that it got bashed and dislodged a tube a bit out of its cradle?

    As for the amp, I bought if from the USA and took it to a part time amp fanatic who is an industrial legend in regards to circuitry, he builds amps too in West Yorkshire, he likes using the best components around and so his amps go for £1500+... Check him on google... TRUVIBE it's called... Anyway, he ****ed up the price and charged me £20 for a half-days work.....

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