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    Higher bias on one socket

    corndog71
    corndog71

    Posts : 730
    Join date : 2013-03-19
    Location : It can get windy here

    Higher bias on one socket Empty Higher bias on one socket

    Post by corndog71 on Thu Mar 26, 2020 1:02 pm

    I recently installed the auto-bias board on my VTA-120 but I’m still seeing a problem that I had before the install.  One of my power tube sockets consistently measures 10 volts higher bias than the other three sockets. I find it very strange that this would occur with the auto bias board installed.  All other voltages are as they should be, I think.  Unless there’s something else I should be measuring.  

    Before plugging in the tubes I tightened them and cleaned them as best as I could but I’m still getting this discrepancy.  Any thoughts on what could be causing it?  Bad socket?  Transformer? All 4 plate voltages are the same.

    It doesn’t seem to affect the sound but I lost a tube in that socket prior to adding the auto-bias.  I also checked resistances on the cathode circuits prior to the AB and found no differences in any of the sockets.
    corndog71
    corndog71

    Posts : 730
    Join date : 2013-03-19
    Location : It can get windy here

    Higher bias on one socket Empty Re: Higher bias on one socket

    Post by corndog71 on Thu Mar 26, 2020 1:41 pm

    I figured it out. I have fuses on the cathodes and for some reason the fuse for the bad socket was double the resistance of what the others measured. I replaced it and all is well. cheers
    corndog71
    corndog71

    Posts : 730
    Join date : 2013-03-19
    Location : It can get windy here

    Higher bias on one socket Empty Re: Higher bias on one socket

    Post by corndog71 on Thu Mar 26, 2020 4:06 pm

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