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Post by tronus on May 4, 2017 11:54:45 GMT -7
Hey all,
I got a Jaz 20/40 new in around 2008/09 I think?
I haven't given it much love but have recently been using it a lot more.
I am getting a loud hum. For a while there it was cutting out and dropping in volume when I hit it hard with signal from a overdrive pedal. I'd have to put it into standby and bring it back out to make it loud again.
During this time, I noticed when I stopped using the effects loop, the hum went away.
I took a single 12ax7 and went down the line. At v3, the cutout thing stopped happening. However, the hum is still there, now without even using the effects loop.
Is this another a preamp tube gone bad or maybe a powertube?
I don't have a tube tester available, personally or in the town shop but I have an extra 12ax7 I can try swapping in and out.
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Post by Jaguarguy (Mike) on May 4, 2017 12:44:46 GMT -7
Here's a link to Doc's trouble shooting page. I use this whenever I'm having issues. If I can't figure it out from this, then it's a quick note to Don at repairs@drzamps.com - he can usually help figure it out. drzamps.com/info/faq-troubleshoot/ Have you cleaned your effects loop inputs? A little Deoxit 5 and work a plug into and out of it a couple times. It might help.
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Post by Norrin Radd on May 4, 2017 14:16:15 GMT -7
Have you cleaned your effects loop inputs? A little Deoxit 5 and work a plug into and out of it a couple times. It might help. This worked for me on a similar issue I was having with my Ray. The worst thing that can happen is you clean out all your jacks!
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Post by tronus on Jun 4, 2017 15:00:34 GMT -7
Hey all, thanks very much for the replies!
Can the Send/Return jacks cause this intermittent cut out without anything plugged into them?
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Post by premiumplus (Dave) on Jun 4, 2017 15:46:52 GMT -7
It sure can. Try plugging/unplugging your cord into the jacks, that usually helps. You may need to put a little contact cleaner on the jack contacts, and that's usually best done with the chassis out of the amp. But try exercising the contacts by doing suggestion #1 first.
EDIT: First take a short cable and plug it between the send and return jack, and that'll bypass the contacts in question. If the problem disappears, you know it's the switching jack that's not making contact when the cord is unplugged.
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Post by tronus on Jun 5, 2017 15:10:38 GMT -7
OK, so I jumpered the send and return jacks with a working patch cable. I proceeded to turn up the master to a loud setting and hit the front end with a couple stacked dirt pedals. I got the thing to cut out once and drop to a low volume and stay there until I cycled the power. I exercised the jacks a bit during this cut out and it still remained at low volume (I still need order deoxit) until power cycling.
Does this mean it's in the power tubes? I tried swapping out each preamp tube with a working 12ax7 but I don't have any 6v6's laying around to test.
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Post by tronus on Jul 3, 2017 7:41:49 GMT -7
It's finally behaving! It still tries to sputter every now and then when it gets loud and starts rattling the effects loops jacks but mainly, it's being good.
I worked the jacks a bunch by plugging and unplugging cables. Glad it's back in action.
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Post by zpilot on Jul 3, 2017 9:38:44 GMT -7
I still think you have a bad output tube. If they have never been changed then they are about due. Changing output tubes BEFORE they fail is a good policy.
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Post by tronus on Jul 3, 2017 10:04:18 GMT -7
Yea, that's a good call. I should pop on a fresh set. I wish I had a tube tester so I could find the weak one and swap it out I still think you have a bad output tube. If they have never been changed then they are about due. Changing output tubes BEFORE they fail is a good policy.
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Post by doctorice on Jul 4, 2017 5:04:23 GMT -7
Yea, that's a good call. I should pop on a fresh set. I wish I had a tube tester so I could find the weak one and swap it out I still think you have a bad output tube. If they have never been changed then they are about due. Changing output tubes BEFORE they fail is a good policy. It's important to use a "matched" set of (4) 6V6s in the JAZ. Matching requires a good tube tester and knowledge. Other than the effect on your wallet, you're probably better off buying a new matched quad of tubes than searching for the culprit. Keep the old tubes -- the whole set -- as emergency spares.
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Post by tronus on Jul 9, 2017 9:44:19 GMT -7
Thanks for the reply! I've called around town because I want to attend a jam today and am worried about the amp going down in the middle of it. I can't get a matched quad locally but I can get two matched pairs of Groove Tubes... one pair rated at a 4 and one at a 5. Would this be OK? Thanks for your help! Yea, that's a good call. I should pop on a fresh set. I wish I had a tube tester so I could find the weak one and swap it out It's important to use a "matched" set of (4) 6V6s in the JAZ. Matching requires a good tube tester and knowledge. Other than the effect on your wallet, you're probably better off buying a new matched quad of tubes than searching for the culprit. Keep the old tubes -- the whole set -- as emergency spares.
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Post by tronus on Jul 9, 2017 12:32:30 GMT -7
UPDATE: My poor amp is far worse off than tubes. I took it to a tech today to test the tubes and I was playing through it while he first checked for microphonic tubes.
Earlier today it was sputtering again and the reverb was cutting in and out. I had some extra 12ax7's around so I swapped out v1 and the sputtering stopped... The sputtering stopped but the reverb was being goofy still.
At the tech's shop the reverb was behaving again but the vibe wasn't working anymore. All of the sudden two of the power tubes (far right set) started glowing.
He thinks it's a bigger issue than just tubes. He's going to test them all but I am also want to try to put him in touch with Dr. Z. Maybe he will be like "oh, that's this and that..." or have some sort of inside builder knowledge.
Is this a thing? Is Dr. Z accessible? I've found the repair phone number but it's Sunday so I will try tomorrow.
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Post by doctorice on Jul 9, 2017 13:53:33 GMT -7
UPDATE: My poor amp is far worse off than tubes. I took it to a tech today to test the tubes and I was playing through it while he first checked for microphonic tubes. Earlier today it was sputtering again and the reverb was cutting in and out. I had some extra 12ax7's around so I swapped out v1 and the sputtering stopped... The sputtering stopped but the reverb was being goofy still. At the tech's shop the reverb was behaving again but the vibe wasn't working anymore. All of the sudden two of the power tubes (far right set) started glowing. He thinks it's a bigger issue than just tubes. He's going to test them all but I am also want to try to put him in touch with Dr. Z. Maybe he will be like "oh, that's this and that..." or have some sort of inside builder knowledge. Is this a thing? Is Dr. Z accessible? I've found the repair phone number but it's Sunday so I will try tomorrow. Send a note to repairs@drzamps.com. They generally respond pretty promptly during the work week. In the past they helped a local tech service one of my Zs. You always have the option to send the amp back to the factory. The repair crew will put it right. Dr Z Repairs
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