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Post by Kris (aka smalltownsongs) on May 8, 2013 6:22:01 GMT -7
So at rehearsal the other night I break out the Maz for rehearsal. 15 minutes in, I'm reaching for the Master Volume cause it sounds like I'm disappearing in the mix. Then my headroom is going. I switch to another amp and decide to check on this guy later thinking maybe my Power Tubes just crapped out. So being the curious guy I am rather than just swap tubes and roll on I pulled the chassis to take a peek. Look what I found! that lil guy looks a bit toasty there next to the Filter Caps, doesn't he? You can see even the leads have a little cook on 'em. So, wise friends: What do you surmise? Power tube went out and took this guy with it? Vice Versa? I'd like to fix it up soon, any idea what value that blue guy is supposed to be or where to quick snag one? Maybe it's something more involved and I'd love to hear your thoughts! Some background: I bought this amp in head format from another Z brother, had the plates flipped and threw it into a beautiful pine cab from Harvey. Hadn't played it up until that point other than a quick plug in and test in the basement once I received it and then once I put it in the cab. The first full band crank up was when this happened. I'm very familiar with what the Maz can do, which was why I just shut her down and went to another til I can get her back up!
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Post by benttop (Steve) on May 8, 2013 8:27:20 GMT -7
Actually that's a resistor. Could have been damaged by a bad tube somewhere along the trail. I do not know its correct value but I've seen other gut shots of Maz's around here - you might find one close enough to see the color bands.
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Post by Kris (aka smalltownsongs) on May 8, 2013 8:31:22 GMT -7
Thanks Steve, yup I should know the diffs between caps and resistors by now Just needed some more coffee flowing in the system!
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Post by Deleted on May 8, 2013 9:31:44 GMT -7
Regular output tube changes can save a lot of headaches. I had to learn this the hard way. You will save time and money on amp service, repairs, S&H charges.
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Post by zpilot on May 8, 2013 11:11:15 GMT -7
This accents another point that I became aware of when I started using "Z" amps. I have been servicing tube amps for a long time so I've usually had schematics and parts lists for all of my amps. I don't have any for my "Z" amps so for future reference I have taken closeup digital photos of all of the chassis and noted the component values. That way if the markings are damaged from heat I will know what to replace it with. All of the parts except for the transformers are readily available from Mouser or Allied or several other suppliers. I suppose you could also get them from Dr. Z service. Dr. Z amps are relatively simple circuits and really easy to work on compared to printed circuit boards. If you don't want to send your amp back to Dr. Z for service I suggest you do what I've done. Make sure you note the color codes on the resistors because sometimes they won't show correctly in a photo.
Fortunately I have never had a "Z" amp fail other than power tubes and that is normal and I've put hundreds of hours on them. One of the reasons I have converted to "Z" amps is because they are road worthy. In fact my repair skills are getting a little rusty.
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Post by Albert on May 8, 2013 11:42:38 GMT -7
I would change them both were one fails the other is soon to follow
Give those caps a good look also...
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Post by DRZ on May 8, 2013 18:07:35 GMT -7
That is a 2.2K 3 watt flame proof screen grid resister. A run away EL-84 will cause that. A fresh set of EL-84's and a replacement resistor is all you need .
DR.Z
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Post by Kris (aka smalltownsongs) on May 8, 2013 18:15:22 GMT -7
MUCH love and thanks Doc!
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Post by Eddie on May 8, 2013 21:59:55 GMT -7
I had that exact same resistor get taken out in my MAZ about 3 or 4 months ago. In fact, I'm not sure how long it was like that. I just happened to open up my amp and I saw what you saw in yours. I couldn't tell what value it was because the colored bands were charred. I emailed the shop and Don D. told me it was probably toasted by a bad tube at some point. I actually went up in rating when I replaced mine - I went with a 5 watt 2.2k flameproof. Don said it wouldn't hurt to go up in rating to a 5W, and I just so happened to have a 5W 2.2k in my parts box - unused! Providence. It's been running great ever since.
This experience made me think it's probably a good idea to open up any tube amp and have a little look around every few years.
Best, Eddie
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Post by Kris (aka smalltownsongs) on May 9, 2013 6:25:45 GMT -7
Thanks Eddie, any idea where to pick up flameproof 2.2k's? I can seem to find 2.2k 3w & 5w but nothing flameproof...
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Post by Eddie on May 9, 2013 23:36:20 GMT -7
I used a metal oxide type resistor like the one that was in there originally, only I went with a 5W. The metal oxide type is flame resistant. You could probably also use a cement type (like the big Xicon 150 ohm 10W to the left in your pic) but those are a little big, and it wouldn't match the type your amp has now. Before going that route, I would check with the Z shop gurus. Here are some links to both the 3W 2.2k and the 5W 2.2k Metal Oxide resistors from a few sources: 3WeBay
Mouser
Tube Depot (be sure to select 2.2k from the drop down menu)
5WeBay 5WMouser 5W
MojoTone 5W (cement type)
Again, just double check with the Doc's crew first if you decide to go with a wire-wound cement resistor like the one in that last link. It should be fine. The other links are all for Metal Oxide type resistors which are what your Z Amp uses now for the two resistors next to the big capacitors. I don't want to put words in Don Depew's mouth, but I believe his reasoning for telling me I may want to go up in rating was because something happened in that spot that stressed the resistor to the point of burning it. Going up in rating from 3W to 5W just adds a little peace of mind. Let us know how you get along with the repair. Feel free to send me any questions, and of course, the Doc's shop will talk you through the repair as well. Just be careful and use all the normal precautions. Best, Eddie
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Post by Eddie on May 9, 2013 23:40:09 GMT -7
Oh, one more thing... You probably know this, but just in case and for others that may need the info - 2.2K 4-band color code is Red/Red/Red/tolerance. I wasn't able to tell the code on my toasted one either because the color had turned black.
And... it's always a good idea to check the value with your ohm meter before you wire it into the amp. You never know for sure until you check it. :-)
Eddie
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Post by Kris (aka smalltownsongs) on May 10, 2013 5:41:32 GMT -7
SUPER SUPER AWESOME! Many thanks and much love! Kris
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