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Post by rckline on Aug 23, 2014 18:02:55 GMT -7
Hello friends-
My beloved MAZ 18R has started making wierd non-musical sounds. Looking on the threads, similar finds but nothing matched. it started out of nowhere with an static pop every 5 minutes or so. When I knocked the amp gently on the top, a whole myriad of static pops, noise, buzzes and LOUD reverb tank sounds. It sounds in distress. When I power up again, there's a fairly loud background hiss that wasn't there before, and then the chorus of pain starts up when any input, guitar or banging on the top, begins.
I live for this amp, and it's fairly new (2012)and has never been taken out of the studio, nor has any work been done other than replacing the power tubes months ago.
Any help or advice would be greatly appreciated.
Oh- I saw the Good DrZ's advice about the treble know, but it had no effect here.
Thanks!
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Post by Jaguarguy (Mike) on Aug 23, 2014 19:07:25 GMT -7
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Post by headshrinker (Marc) on Aug 23, 2014 19:13:24 GMT -7
Pull the phase inverter ( the one closest to the power tubes)and give the amp a thump or two. If it's still there it's the output tubes. My guess it's one of your preamp tubes. You can tap on them with the eraser end of a pencil and see if you can find the tube. Or get a known good 12AX7 and start subbing one tube at a time from the far left looking at the back. If the noise is still there put back the one you pulled and move to the next. If it goes away you found the tube. When you get to the 12AT7 you can use the 12AX to test it. If that turns out to be the culprit you can leave the 12AX in if you like the sound, if not go get a 12AT7 and put it in and keep the 12AX for a spare. Also check that the plugs that go from the reverb tank to the amp are in tight.
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Post by BritInvasion on Aug 23, 2014 19:44:30 GMT -7
^^ I agree with Marc. Guarantee you it's a tube(s).
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Post by rckline on Aug 23, 2014 19:47:21 GMT -7
Thanks for the replies- putting in new power amp tubes was a big step for me as far as tube replacement goes, and what you folks have said so far is a perfect place for me to start. I sincerely appreciate it...
Feel free to keep the advice coming!
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Post by benttop (Steve) on Aug 23, 2014 19:53:56 GMT -7
Make sure your chassis bolts are tight. They keep the chassis in contact with a metallic plate in the cabinet. If the bolts come loose, you can get all kinds of popping and scratchy static.
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Post by rckline on Aug 24, 2014 15:50:57 GMT -7
OK-I pulled the phase inverter tube, and the problem disappeared. Now I'll order a new one from KCA and update when it's installed.
Thanks everyone!
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Post by headshrinker (Marc) on Aug 24, 2014 16:26:27 GMT -7
If you pulled the phase inverter and it went away that tells you that the problem was one of the preamp tubes but not which one. It could be the phase inverter but it could be one of the other ones. Before you order the tube put the phase inverter back and do the tap thing I said above. When you tap the bad tube you'll hear the noise. Once you find that order that tube. If you have already ordered the phase inverter it is a 12AX7 and will work in the other positions if it turns out to be one of them. It will also work for the 12AT7. Most folks like go with the 12AT it came with in that position but some folks like me prefer the 12AX.
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