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 Carvin X100B Unbalanced Bias View next topic
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guitartrav
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PostPosted: Sun Jan 22, 2017 9:16 pm   Reply with quoteBack to top

Just recently purchased a 1984 Carvin X100B Head. All the tubes checked out good except for one pre-amp tube. Replaced the pre-amp tube. I replaced all the electrolytic caps and out of spec resistors. The problem I am having is that when I check the bias of the tubes V4 and V5 are only drawing 17mA each at the grid. V6 and V7 are drawing 24.5 mA each at the grid. All the tubes are 475 volts at the plate and 471 volts at the screen. I am measuring -54.5 volts at pin 3 of each tube. I have checked all the resistors at each tube and they are all within spec. I have tried putting different tubes in with the same result. I am at a loss here. Anyone got any ideas what is going on? Thanks.
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