Laney GH50L additional bias control?l

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by supergenius365, Feb 7, 2006.


  1. supergenius365

    supergenius365 Silver Supporting Member

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    I was told that despite having a switch on the back panel to switch between different tube types without re-biasing, that there is an additional trim pot (?) inside the unit to fine tune the bias. Any experience anybody?

    Thanks
     
  2. supergenius365

    supergenius365 Silver Supporting Member

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    Bump for an old thread.

    I really need help on this one!

    Thanks,
    J
     
  3. supergenius365

    supergenius365 Silver Supporting Member

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    Thanks for the reply!

    I bought it used and have nothing except a users manual I got from the Net.

    I just found a post on Google from a player who got a reply from Laney saying that they recommend having the amp rebiased when changing tubes, but there is no mention of that in the manual.

    I'll try to find a schematic.

    Thanks,
    J
     
  4. supergenius365

    supergenius365 Silver Supporting Member

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    OK,

    I found some references to having the head rebiased by a pro, so obviously there is more to it than just the tube selector switch.

    Here is the original problem:

    Replaced 2 Sovtek 5881's w/ 2 SED Winged C 6L6's.
    After 10 minutes of minimal playing, I smelled something burning.
    One tube was bright orange and the other was bright blue.

    Is this a tube problem (bad tubes) or an amp bias problem?


    Thanks
     
  5. supergenius365

    supergenius365 Silver Supporting Member

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    How about really bright blue? Bluer than average?

    Would the red plating tube cause the superblue tube?

    Thanks for your answers. I don't really know squat about this stuff!
     
  6. Dave C

    Dave C Gold Supporting Member

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    I couldn't find a schematic of the 50 ,but the GH100L is available and shows a bias trim pot. I would expect the 50 to be similarly equipped.
    Dave C
    http://www.schematicheaven.com/
     
  7. rockon1

    rockon1 Member

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    If you put the old tubes back in and one doesnt red plate I'd say you got a bad tube.
     
  8. Thames

    Thames Member

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    I got em ! Drop me an email.

    Yes, it has BIAS pot inside. I installed a pair of 1-ohm resistors to facilitate BIAS adj.
     
  9. supergenius365

    supergenius365 Silver Supporting Member

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    This is why I love TGP!

    So many helpful members.

    Thanks!
     

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