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Divide and Conquer

4/14/2003 6:52 PM
Deltablues	Divide and Conquer You have two different channels with two independent tone stacks. Does this "brittleness" sound the same on both sides when the eq settings are set to the same levels? If it does, then it's not in your tone stack or eq. Pull your reverb tubes... Still the same? Then it's not in your reverb send/return circuitry. Pull your tremolo tube... Still the same? Then it's not in your Tremolo ciruitry. Got new speakers in there...? (Good chance this is your culprit). Then plug the amp into another cab with worn in speakers. If the brittleness goes away, then you know your speakers need some break in time. Running a GZ34 as the rectifier? This'll pump up the treble. Try rebiasing with a 5U4GB and see if this is the culprit. Run a known good 12AX7 down the line one position at a time. See if you have a crappy tube in there that's corrupting the signal path. If all that fails, get your AB763 layout and start checking all the component values start to finish. There's always the possibility that an incorrect value component has found it's way in there either from the crappy QA of the original CBS era construction or done later on by a tech that wasn't paying close attention during a routine repair. All things being equal, there's nothing magic about the AB763 design that would make one amp noticeably more trebly than another.

4/14/2003 6:52 PM

Deltablues

Divide and Conquer

You have two different channels with two independent tone stacks. Does this "brittleness" sound the same on both sides when the eq settings are set to the same levels? If it does, then it's not in your tone stack or eq.

Pull your reverb tubes... Still the same? Then it's not in your reverb send/return circuitry.

Pull your tremolo tube... Still the same? Then it's not in your Tremolo ciruitry.

Got new speakers in there...? (Good chance this is your culprit). Then plug the amp into another cab with worn in speakers. If the brittleness goes away, then you know your speakers need some break in time.

Running a GZ34 as the rectifier? This'll pump up the treble. Try rebiasing with a 5U4GB and see if this is the culprit.

Run a known good 12AX7 down the line one position at a time. See if you have a crappy tube in there that's corrupting the signal path.

If all that fails, get your AB763 layout and start checking all the component values start to finish. There's always the possibility that an incorrect value component has found it's way in there either from the crappy QA of the original CBS era construction or done later on by a tech that wasn't paying close attention during a routine repair.

All things being equal, there's nothing magic about the AB763 design that would make one amp noticeably more trebly than another.

Replies:

Jack Koochin OK guys, awesome input. I forgot t... -- 4/15/2003 6:15 PM