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EZG50 Hum
Feb 21, 2015 14:16:57 GMT -7
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Post by otherone on Feb 21, 2015 14:16:57 GMT -7
Posted this in amp troubleshooting section as well. When post volume is 9oclock or lower and pre volume at any level...no hum. When post volume greater than 9oclock there is noticeable hum. Doesn't happen when raise pre volume, only post volume. Just got brand new NOS tubes. I believe everything has been fine with them. Think I just noticed this hum. Any thoughts?
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Post by headshrinker (Marc) on Feb 21, 2015 14:36:19 GMT -7
Did you bias the amp when you changed the tubes? If not it may need to be rebiased. Also were the tubes matched? If not that could be the hum. Lastly, even with NOS tubes you can get a bad set. If it didn't do it before you changed the tubes and you didn't rebias put the old ones back in and see if it goes away. Then you know it's either the bias or the tubes. If you did rebias then you would have to rebias again for the old tubes and if it goes away you know it was the new tubes. If it stays the same, with both sets it's something else. I'm assuming you only changed the power tubes. If you changed the preamps too it could be one of them. Pull the phase inverter. If it goes away it is likely in the preamp section, if not it is likely the power tubes. Here's the link to what DrZ says to do first. drzamps.com/trouble_shooting.html
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EZG50 Hum
Feb 21, 2015 14:59:52 GMT -7
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Post by otherone on Feb 21, 2015 14:59:52 GMT -7
Yes new NOS power tubes, GE, matched and biased professionally at 28mamps. All new NOS preamp tubes. Tungsol ax7 v1, RCA at7 v2, ge 1950s ax7 v3, ge at7 v4, ge Mullard 5ar4. Got over 2 months ago. Gigged, played, all has been well until today. I'll try changing out v4 phase inventor and see what happens
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EZG50 Hum
Feb 21, 2015 15:08:01 GMT -7
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Post by otherone on Feb 21, 2015 15:08:01 GMT -7
So I pulled out v4 and sound went away what does that mean? I need a new at7 in v4? Or one of other preamp tubes is bad? Thanks
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Post by headshrinker (Marc) on Feb 21, 2015 15:08:32 GMT -7
Don't change it. Just pull it and leave it out to test it. That will determine if it's a power tube or preamp tube. If it's a power tube, try the old ones back in. Even if they are not biased perfect it will give you an idea if they might correct it. If it's preamp side, get a known good 12AX7 and sub it for V1. If no change put the old one back and move to V2. etc. If it goes away you found the bad preamp tube. You can use the 12AX to check the 12AT too. It's been said here more times than I can count, 98% of tube amp problems are tubes. Also be sure to try the amp in another location on a different circuit, with a different guitar, different cable, no pedal board etc. to eliminate non amp reasons.
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Post by headshrinker (Marc) on Feb 21, 2015 15:12:01 GMT -7
Just saw your post. That means it is likely a preamp tube. Can't tell which without trying them. After eliminating all of the nonamp things I mentioned above. Start the sub process. Keep us posted if you find something that solves it. It will help folks in the future.
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EZG50 Hum
Feb 21, 2015 15:24:18 GMT -7
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Post by otherone on Feb 21, 2015 15:24:18 GMT -7
Eliminated all non amp things. So I should put v4 back in and then swap out v1,v2,v3 one by one to see if hum goes away? Thanks
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Post by headshrinker (Marc) on Feb 21, 2015 15:44:14 GMT -7
Yep you've got it. If you get that far be sure and do V4 too.
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EZG50 Hum
Feb 21, 2015 15:44:26 GMT -7
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Post by otherone on Feb 21, 2015 15:44:26 GMT -7
Looks like bad v1. Problem solved. Thanks so much. Of course it was the most expensive preamp tube!
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Post by headshrinker (Marc) on Feb 21, 2015 15:51:11 GMT -7
Of course. always is. Glad you got it sorted out. Like I said, if it's a tube amp the problem is likely tubes. Before you toss the tube, You may find that it works in another position in the amp or in another amp. Might want to try it in V3 in that amp just for the fun of it. Swap V3 to V1 when you do. That GE might sound great in V1. Just be sure and mark it as possibly bad. You can use a sharpy on the tube itself if you don't have a box.
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EZG50 Hum
Feb 21, 2015 17:11:21 GMT -7
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Post by otherone on Feb 21, 2015 17:11:21 GMT -7
Interesting story. So I tried v1 tungsol in 3 other amps...and no hum or buzz. Sounded great. Turns out that for some reason the dr z does not take well a 17mm tube in v1. All the other NOS 14mm tubes have no buzz. So, I put the tungsol in my '66 pro reverb and no issues with the 17mm tube there and it sounds great. Ended up putting a NOS RCA 7025 in v1 of Dr Z and it is a great replacement for the tungsol. Sounds great with the other tubes. So, this turned out to be a very tube specific problem...interesting! Thanks for all the help
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Post by corbeano on Dec 30, 2015 16:33:49 GMT -7
Just to make sure,,, I have a pretty good hum when turning up the post (around 9). I can check all the preamp tubes with a good 12x7?
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Post by headshrinker (Marc) on Dec 30, 2015 17:07:41 GMT -7
Yep. It won't cause any problems. Just make sure it's a known good one.
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Post by corbeano on Dec 30, 2015 19:24:37 GMT -7
I tried all Pre amp sockets with a newer tube I. I still get a pretty good hum at 9 and gets louder from there.. I can turn the pre up a lot with out hardly any noise..
I checked the bias on the power tubes. MY fancy Craftsman thang said one power tube was 30ma and the other 31ma... I would assume thats close enough.. I did all this with the reverb off of course. Maybe this is normal... I think its odd i get nothing till 9.
I also pulled out the phase inverter and turned the amp on. quiet as can be. I mean dead silent. I don't know.
I wouldn't hear at a gig,,, but when tweaking the amp in music room, it is a tad annoying... Anyone got something about this?
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Post by corbeano on Dec 30, 2015 19:30:07 GMT -7
Added note. I tapped on all the preamp tubes. V2 made a little noise with the reverb on.
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juicecastle
New Member
That's my dad! and he was awesome!!!
Posts: 43
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EZG50 Hum
Dec 8, 2016 19:11:08 GMT -7
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Post by juicecastle on Dec 8, 2016 19:11:08 GMT -7
Just saw your post. That means it is likely a preamp tube. Can't tell which without trying them. After eliminating all of the nonamp things I mentioned above. Start the sub process. Keep us posted if you find something that solves it. It will help folks in the future. hi all I just got am EZG and I'm hearing the same thing, so I want to try this process of test which tube could be the culprit. But I'm not to savvy so forgive for asking a newbish question when testing each tube how is that done exactly? Do you pull one out then plug in turn the amp and play or just turn the amp on and turn the knobs up? Sorry to get late on this post but was hoping to find an answer to that hum.
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