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Post by nolesj on Jan 8, 2018 11:50:09 GMT -7
Hey guys! First post here, though I've been lurking for a while. I recently acquired a 2008 or 2009 MAZ 18 JR (no reverb) head in a trade about two months ago. Until today, the amp has been flawless. Today, after a short warmup (as I usually do), I flipped on the standby switch and was greeted by a loud popping/scratching type noise through the speakers (like you would get trying to plug in your guitar cable with a live amp). I turned the amp off immediately (no smoke or weird smells), and started it back up. Now, there is a loud hum that doesn't change with either volume control, or tone/cut controls. It's there all the time, all controls on 0 or wide open, guitar plugged in or not. It still makes sound if I play through it, though the volume does seem to be a bit reduced from normal.
I have some spare preamp tubes, and I swapped preamp tubes one by one with no change (reinstalling the original preamp tube into its original place after the swap). I have one spare EL84, so I swapped it into each power tube socket (just to try), and no change. I do NOT have a spare rectifier tube, but do you think the rectifier could cause this? I've tried plugging the amp into a different outlet, but again, no dice.
Any ideas? All would be appreciated.
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Post by purpletele on Jan 8, 2018 12:20:00 GMT -7
Hey guys! First post here, though I've been lurking for a while. I recently acquired a 2008 or 2009 MAZ 18 JR (no reverb) head in a trade about two months ago. Until today, the amp has been flawless. Today, after a short warmup (as I usually do), I flipped on the standby switch and was greeted by a loud popping/scratching type noise through the speakers (like you would get trying to plug in your guitar cable with a live amp). I turned the amp off immediately (no smoke or weird smells), and started it back up. Now, there is a loud hum that doesn't change with either volume control, or tone/cut controls. It's there all the time, all controls on 0 or wide open, guitar plugged in or not. It still makes sound if I play through it, though the volume does seem to be a bit reduced from normal.
I have some spare preamp tubes, and I swapped preamp tubes one by one with no change (reinstalling the original preamp tube into its original place after the swap). I have one spare EL84, so I swapped it into each power tube socket (just to try), and no change. I do NOT have a spare rectifier tube, but do you think the rectifier could cause this? I've tried plugging the amp into a different outlet, but again, no dice.
Any ideas? All would be appreciated. nolesj, It can definitely be the rectifier and in fact most likely. At this point I would recommend changing the power tubes as well to a new matching set. You may also want to check the fuse size and have two handy for the future. Occasionally there may be an event where the power tubes go and they burn a grid resistor. You wouldn't get anything if that was the case.
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Post by nolesj on Jan 8, 2018 13:12:21 GMT -7
Thanks purpletele! I'll give the old rectifier a try!
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Post by purpletele on Jan 8, 2018 15:08:19 GMT -7
Thanks purpletele! I'll give the old rectifier a try! While you are working on it you should clean the input and fix loop jacks. I chased a-ghosting tube issue, like little floaters of static, ithat turned out to be the FX loop jacks. Let us know how it goes, most everyone heremakes mental notes BV
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Post by Chilly Gibbons (Todd T.) on Jan 8, 2018 16:37:40 GMT -7
Were you able to get a look at the power tube and rectifier during the noisy period? I’ll bet one of the el84s was arcing and took the other one with it. Like Purple said, I’d replace the power tubes and rectifier. You should be good to go. Cheers!
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Post by nolesj on Jan 9, 2018 17:58:36 GMT -7
ttepper- you were right on target! I took the amp out of the chassis and turned it on. One of the EL84's looked like the fourth of July! I have ordered a replacement set of tubes (all of them) along with a spare set. Thanks for all the help!!
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Post by Chilly Gibbons (Todd T.) on Jan 9, 2018 18:33:48 GMT -7
Great! That should get you going again. Happy New Year!
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Post by headshrinker (Marc) on Jan 9, 2018 20:47:24 GMT -7
If you liked the way the amp sounded before the power tube went south, Don't change the preamp tubes until they go south too. Maybe the phase inverter, the one closest to the power tubes, not the rest. Likely your tone will change if you do. Especially if you do them all at once. If you do change them out, do one at a time and then listen, so you know what tube changed the tone. Rectifier is your call, it's good to have a spare.
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