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Post by wallysr on Sept 19, 2015 12:21:44 GMT -7
Hello. New to Dr. Z amps. New to Z Talk. I've tried to utilize the search function, but haven't found my problem addressed yet (sorry if my search-fu is weak...).
I bought the amp (Maz 8 Head) new a few months ago. I've only put a few hours on it. It played fine today for about half a hour or so, then began crackling and hissing. I took a quick video with my iPhone; hopefully the quality is good enough to capture the crackling and hissing.
Per the video, the issue was more noticeable in the hotter configurations (Pentode, Hi input). It was also present regardless of whether I was playing or muting the guitar with my palms. Also, adjusting the knobs didn't have any effect on the issue.
(more below the video)
At this point I was thinking it's probably a bad tube. I went to the "Troubleshooting" section of Dr Z's website and followed the instructions verbatim. Removed all tubes. Powered amp up. Powered amp down. Fuse good. Reinstalled rectifier tube. Powered amp up. No arcing or sparking. Powered amp down. Fuse good. Installed power tube. Powered amp up. No arcing or sparking or plating observed. Powered amp down. Fuse good. Installed the preamp tubes. Powered amp up. No sound.
...and that's where I'm stuck.
After reinstalling all the tubes everything appears to be normal, except I have no sound. None of the pins appear to be missing from any of the tubes. None of the tubes show obvious signs of catastrophic failure.
I began swapping out 12AX7 (edited to correct tube model number) tubes since I have some spares. That didn't do the trick. Swapping in the last 12AX7 (edited to correct tube model number) I heard a disconcerting POP after about 10 seconds. The fuse was still good, but I stopped there. I don't have spares for the other tubes and don't really want to push mu luck.
It looks like I'll have to take the amp back to my dealer to have them take a look at it (or send it back to Z since its still under warranty).
I'm just curious if there's anything obvious that I'm missing.
Thanks.
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Post by headshrinker (Marc) on Sept 19, 2015 13:13:22 GMT -7
I would again try swapping a good 12ax7 for the preamp tubes one at a time. If no change put the old one back. When you get to the 12AT7 you can use the 12AX7. It won't hurt anything. If you have no sound It's likely the phase inverter which is the one closest to the power tubes. Any chance the amp was on when you put that one in? If so that could be the pop. Probably didn't hurt anything if it was on. The sound on the recording sounds like a tube problem. Tubes can go bad but look fine when you look at them. Lighting up is not a sign of whether a tube is working or not. They often light up when they are bad. Last couple of obvious things, guitar is turned up? guitar cable is good? speaker cable is good? and plugged in? to the correct jack? speaker good? Those aren't to assume you are stupid, but things I have done while thinking I had an amp problem.
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Post by wallysr on Sept 19, 2015 18:47:54 GMT -7
Thanks for the reply. No offense taken regarding the common sense stuff. In order to rule it out I ran another head through the same speaker cab, cable, guitar and guitar cable. No issues.
I swapped out the 12AU7 with a 12AX7 (edited to correct tube model number) per your advice. Things got weird. It cracked and popped like hell for about 15 seconds (more sound than I got out of the amp since it started acting up this morning), then squealed like kerry king was letting the air out of a balloon for another 15 seconds, then resumed cracking and popping obnoxiously. At that point I got frightened and turned everything back off.
I suppose its possible I swapped out a bad 12AU7 and replaced it with a bad 12AX7 (edited to correct tube model number). I also suppose its possible I have a bad power or rectifier tube (I wouldn't think the rectifier tube would be part of the signal path) since I wasn't able to test them (my spare el84's fit a larger socket so I can't swap them in [edit: it turns out I was thinking of EL34's]). Everything I've observed says "tubes," but I'm a little concerned with the lack of progress. I guess I'll order new power and rectifier tubes and if that doesn't do the trick I'll send the amp back in.
I'll let you know how it goes.
Thanks again.
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Post by simpleton on Sept 19, 2015 19:47:41 GMT -7
Maybe take into the dealer you got it from to do some tube swapping before you buy new ones. Super frustrating when these things delay the joy of a sweet amp.
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Post by benttop (Steve) on Sept 19, 2015 22:14:41 GMT -7
Does it make these sounds without the guitar plugged in? Does it make them with all the volumes turned down? Does the tone control affect the sound of the popping and static?
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Post by digs57 on Sept 20, 2015 7:24:50 GMT -7
would look at your v1 with some known fresh tubes...most every issue (non z amps included) I have had that is the culprit
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Post by zpilot on Sept 20, 2015 9:37:49 GMT -7
#1 "Adjusting the knobs didn't seem to have any effect on the issue" #2 "Installed the preamp tubes. Powered amp up. No sound".
These two things probably narrow it down to the power amp. The phase inverter tube (a 12AX7) is actually part of the power amp even though it is commonly referred to as a pre-amp tube. Make sure you have a good one in there. Current manufactured 12AX7s don't last very long in that spot and I replace them every other time I change the power tubes. That shouldn't be an issue with a new amp though. I would suspect the PI. It's the 12AX7 closest to the power tubes.
A good way to test the power amp is to run a line level signal into your effects loop return.
What are you meaning by "12AX87"?
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Post by wallysr on Sept 20, 2015 13:20:33 GMT -7
12AX87 was a brain fart. The chart inside my amp says 12AX7. I've been reading a bit over at AX84.com and conflated the two. Sorry. It was beer thirty.
The pool of spare 12AX7's I'm pulling from are JJ ECC 83Ss from a Marshall JCM 2000. I had no reason to suspect any of them had gone bad, but I retubed the entire amp when I replaced the mother board (I had a low serial number amp with a bad motherboard. It was a known issue with those...sorry to digress).
Anyway, I've swapped a few of them in with no improvement. Well...the amp is completely unresponsive so I guess that's an improvement over the popping and cracking.
I've got a Vox Lil Night Train I can use to "prove" out the 12AX7's and 12AU7. I should have thought of that earlier. If i can prove out all the 12AX7's and the 12AU7 I'll replace the other two. If that STILL doesn't work I'll have my dealer take a look at it and/or pursue a warranty repair. I just want to make sure I've done my due diligence first.
I won't have much time during the week, but whatever happens I'll make sure to update the thread eventually in case anybody is curious. I really appreciate the help.
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Post by simpleton on Sept 20, 2015 14:05:17 GMT -7
Definitely curious... Keep us posted
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Post by wallysr on Sept 24, 2015 17:31:26 GMT -7
Quick update: I ran the 12AX7's and 12AU7 through my lil night train. No issues. The EL84's and 5AR4 I ordered (JJ's from eurotubes) were estimated to have been here today, but they didn't quite make it yet.
It was suggested above that I run a line level signal into my return to test the power circuit. I'll confess my ignorance and admit I had to look up the difference between line and instrument level. Not much apparently, but maybe enough to matter... Unfortunately I don't think I have any equipment that will generate a line level unless: while reading I stumbled upon amp slaving. I'd never heard of that before but it sounds awesome! I'm a little nervous to try it on the Maz 8 until I resolve this issue, but I don't think it would hurt to "send" a JCM2000 effects loop signal into the "return" of the Maz 8 (and vice versa once I get everything sorted out). Different speaker cabinets so I can leave both amps "loaded."
I don't want to tear this amp open quite yet and potentially void the warranty (just in case it turns out not to be a tube issue), but I don't suppose there are any fuses I could check other than the main?
Thanks again, and I'll keep the thread updated as I make progress.
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Post by zpilot on Sept 24, 2015 20:50:43 GMT -7
Sounds like you understand what I was talking about with your effects loop. Just be sure to start with your signal levels at 0 and bring them up slowly to avoid any big surprises.
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Post by wallysr on Sept 28, 2015 19:29:29 GMT -7
Well my tubes showed up this evening...finally... I'd like to pretend I have the self control to test-drive these tubes without waking my wife and toddler but frankly we all know that's not going to happen. Hopefully I can update tomorrow. If not: some time this week.
...never got the guts to slave it. Not until everything is in working order (keep the variables to a minimum when troubleshooting).
Later!
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Post by wallysr on Sept 29, 2015 20:01:37 GMT -7
I swapped in a new EL84. No change. New rectifier tube. No change. Never even made a sound. Poor lil fella. Metered my fuse just for fun. .4 ohms. Re-verified guitar, cables, cabinet, etc are working by playing through another head.
At this point it seems pretty reasonable to suspect there's a bigger issue. I'm not going to look any further, as I don't want to risk voiding my warranty.
Things happen. No big deal. I'll initiate the warranty process and see where it goes from there. I'll update as I'm able, but I'm not really expecting the amp repair to come back with a RCFA.
Thanks again for the help.
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Post by "Z" Steve on Sept 29, 2015 20:57:31 GMT -7
Not sure where you live Wally, but I've read that the Doc's turn around time is pretty fast.
Good luck on a great amp.
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Post by simpleton on Sept 29, 2015 21:37:23 GMT -7
bummer...I had to do a repair with my Therapy and they fixed it in one day. Still no fun.
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