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Post subject: BLACKFACE TWIN AB-763
Posted: Sun May 24, 2009 4:03 pm
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The Vibrato channel on my 1967 Twin sounds terrible. The Normal channel sounds ok but I don't use it, it sounds dry without reverb. I removed the amp from the speaker cabinet and started checking voltages with a FLUKE meter. I found the 12AX7 pre-amp tube had negative voltage on pins #2 and #8. I changed the 20 MFD 500 DCV capacitors all the orange dip .1 MFD and the .047 MFD capacitors with no change in voltage. Does anyone have any suggestions as to what to look at next?


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Posted: Mon May 25, 2009 4:04 pm
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Try swapping out the tubes and rectifier...maybe try the rectifier first, if no better, the tubes one at a time.

Good luck!

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Post subject:
Posted: Thu May 28, 2009 7:11 am
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Yeah a negitive voltage sounds like a bad tube.


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