Members twotimingpete Posted November 3, 2008 Members Share Posted November 3, 2008 a few weeks ago I picked up a like-new carvin nomad. this is an all tube amp. https://www.carvinguitars.com/products/single.php?product=NOMAD anyway, it's been working fine. today, though, problems! I was warming up the amp as per usual on "standby" mode, and when I reached back to turn it fully on, I accidentl yturned the main power off, so without thinking, I just turned it back on. I heard a small (not loud by any means) crackle noise. I didn't think much of it. after a couple minutes of playing, I noticed the amp started putting out some kind of shuffling crackle noise... popping.. shuffling.. hard to explain. I initially thought my guitar's output jack was flaking out, but I proceeded to unplug the instrument cable from the amp's input and the shuffling noise continued. so clearly it's the amp. I also noted a very small hint of a burning smell. I took a look at the back of the amp and looked at the four larger tubes. the two on the left were glowing bright orange and the two on the right were dimly lit. I don't know if this is normal or not, I never paid attention until now. anyway, I turned it off promptly. I'm hoping to god this is just a problem with a tube or tubes. can you guys offer any advice? I'm not very knowledgable about how amps work by any stretch of the imagination. Matt Link to comment Share on other sites More sharing options...
Members riffy Posted November 3, 2008 Members Share Posted November 3, 2008 Two glowing bright orange are running away and taking the current from the other two tubes. Sounds like your gonna be taking out a screen resistor or two along the way as well. Get new tubes now. Put them in now. Don't let the tubes cost you more than it should by replacing them now. Link to comment Share on other sites More sharing options...
Members twotimingpete Posted November 3, 2008 Author Members Share Posted November 3, 2008 would bad tubes cause the problems I described? also what is a screen resistor and how do I know if it needs replaced? I hope this doesn't get expensive.. Matt Link to comment Share on other sites More sharing options...
Members womantone Posted November 3, 2008 Members Share Posted November 3, 2008 What you described: One matched pair of power tubes is failing. The solution: Get a new set of matched power tubes Whats a screen resistor? A resistor placed on the grid or screen of the power tube. The grid or screen is internal, the resistor is typically placed on the tube socket. Does it need replaced? No! And do not try to replace it yourself ever unless you learn more about tube amps. Even with the power off the capacitors inside have enough voltage and current to give you a nasty or possibly even kill you. Link to comment Share on other sites More sharing options...
Members twotimingpete Posted November 3, 2008 Author Members Share Posted November 3, 2008 thanks. do you know if replacing the power tubes (these are EL84s) always requires the amp's bias setting to be adjusted, or is there a way to just get what I have now and it would be ok? these say groove tubes on them. Link to comment Share on other sites More sharing options...
Members Radiohead, lol Posted November 3, 2008 Members Share Posted November 3, 2008 You can get some groove tubes EL84s with the same rating (see if there's a number on the tubes of some sort). It's always better to check the bias, however. Also, hijacking for a second (sorry) - one of my amps has what might be a similar problem, but it isn't the tubes. The pair on the right runs hotter than the pair on the left. What could be causing this? Link to comment Share on other sites More sharing options...
Members twotimingpete Posted November 3, 2008 Author Members Share Posted November 3, 2008 I pulled a power tube out and here's exactly what's on it. The Groove Tubes logo etc GTEL84R (6BQ5) and then there's a circle where someone has hand-written the number 7. that's this, yes? http://accessories.musiciansfriend.com/product/Groove-Tubes-Gold-Series-GTEL84R-Matched-Power-Tubes?sku=219168 so I'd need to take this then select the "4-7 gt rating" (I'm assuming that's the handwritten number) talk to me as though you're explaining it to your grandmother. Link to comment Share on other sites More sharing options...
Members Radiohead, lol Posted November 3, 2008 Members Share Posted November 3, 2008 Those would be the Russian made (sovtek) EL84, GT rating 7. And yes, that's what you need to do, however, I wouldn't recommend buying them from there (MF isn't a tube dealer like the tube store, dougs tubes, etc). What I would do is get the non-rebranded russian EL84s, from here for example http://thetubestore.com/ehxel84.html OR these, if the EHX are a bit too pricey http://thetubestore.com/sovtekel84.html and ask them for a quad that is equal to groove tubes rating 7 (I'm fairly sure they can do that). There's probably less of a chance of getting a bad tube, and you'll probably get a quad that falls in the right bias range as long as you request that from them. (if you pick 4-7 from MF, you will get anywhere from ratings 4 to 7, so you can't be sure really) Link to comment Share on other sites More sharing options...
Members twotimingpete Posted November 3, 2008 Author Members Share Posted November 3, 2008 alright, I ordered the first one (the EHX) and I asked for a matched quad equal to a groove tubes rating of 7. hope they can do that. in any case, I really hope bad tubes are my only problem. someone on another forum suggested the transformer could be broken, or it could be a cracked "bias feed resister" or leaky coupling cap, whatever any of that means. at the end of the day, if tubes don't fix it, then I have to take it somewhere, and since tubes are the cheapest option, I'll try that first. I'm also thinking these tubes are better than the stock ones, so it can't hurt to have them on hand even if I need to take the amp in for repair. Link to comment Share on other sites More sharing options...
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