middlecreekguy Posted May 31, 2004 Share Posted May 31, 2004 .....the top of my Rogue Eighty-Eight that is. I did my first tube roll. Not for the fun of it but to fix an intermittent high pitch tone I could hear from time to time. I emailed Mark O`Brien at Rogue who diagnosed my problem. He said one of the smaller tubes was probably going out and I would need to figure out which ones to change. My Rogue sports 4 Sovtek KT88 power tubes, 4 Mullard 12au7a`s and 2 Amperex 12ax7a`s. Being that I have no tester I decided to buy all new small tubes. I got 2 Tesla 12ax7`s and 4 Siemens 5814a`s. Instead of changing all at once I really wanted to hunt down the problem tube. So I started by exchanging the Tesla`s for the Amperex. Bingo. That was it. No more high pitch tone. The amp is dead quiet. I think the Amperex may have had a little more high end detail with the Tesla`s adding slightly fuller midrange. Now here`s the thing that`s got me stumped. I feel like I have so many options now with ways of changing the sound of this amp. Who said you would miss your tone controls when there are so many tubes out there to roll. I am finding it a bit over whelming. Now I`ve got 4 new 12au7`s that I can roll AND I have the option of switching this amp into triode mode. What should I try next? Roll those Siemens in, or flip the triode switch? Decisions, decisions. This newbie tube guy is having a blast. I realize there`s not a right or wrong answer here. Just wanted your thoughts. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 Sorry about the gigantic pictures. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 Another shot from the top. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 You mean to tell me you've been running that beast in ultralinear mode to those Cornwalls all this time?! Throw that S.O.B. into Triode Mode and let those Cornwalls sing!! I'm only putting 12 watts into my KG 5.5s which are 98dB like your Corns, and they are really loud without even pushing the amp. Try it and tell us what you think! I bet you'll like it. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 ---------------- On 5/31/2004 1:44:02 PM middlecreekguy wrote: Another shot from the top. ---------------- Is it just me or does it look like that top right KT88 look like it might have a leak or the getter isn't getting anymore? Looks like a lack of "getter flash" on the top compared to the other KT88s in there. Just thought I would ask. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 I have been wondering this myself. I`ll tell you, I can not hear anything wrong at the moment. But I did want to get some feedback on the looks of that tube. Sounds good to these ears. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 As far as triode mode I guess I`ve been saving the best for last. Wanted to also get an ear for ultra-linear mode so I could differentiate between the two. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 That picture is much better. Thank you. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 Yeah, let's wait and see what others have to say about that one tube before replacing it. There might be nothing wrong with it at all. I'm not sure how that amp of yours works, but you might be able to throw other power tubes in it as well, like 6550, KT66, KT90, or something like that. The KT66 will probably drop the power output a little, but I'm sure it couldn't hurt. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 ---------------- On 5/31/2004 1:57:40 PM middlecreekguy wrote: That picture is much better. Thank you. ---------------- LOL. No problem! Quote Link to comment Share on other sites More sharing options...
Colin Posted May 31, 2004 Share Posted May 31, 2004 Many tube-ophiles go around with their tubes uncovered all the time, NOT even the women object! I must agree with the triode mode on big ole horns. I am surprised however at the carbon build-up on the top of three of those KT-88s. How old is the amplifier? How old are the tubes? I know that some tube amplifiers run hot, meaning they apply a lot of voltage to the tube to get more power out of them and this uses up the tube quickly (NOT a problem if the tube are cheap). Ask the manufacturer to estimate the tube life. If the amplifier isnt old, the tubes are relatively new and the amplifier doesnt run the tubes hot, then the tubes are NOT getting enough ventilation. I have no covers on power amplifiers when I run them; my tubes have very little carbon build-up even after running almost daily for three years. When I kept my covers on my rusty Dynaco ST-70 monoblocks however, my output tubes looked more like yours, ominous storm clouds portending a short life. If the top is more than warm to the touch with the amplifier warmed up, then I say leave the cover off until small children come around. Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 This is taken from Svetlana's site..... "The getter in most glass tubes is a small cup or holder, containing a bit of a metal that reacts with oxygen strongly and absorbs it. (In most modern glass tubes, the getter metal is barium, which oxidizes VERY easily when it is pure.) When the tube is pumped out and sealed, the last step in processing is to "fire" the getter, producing a "getter flash" inside the tube envelope. That is the silvery patch you see on the inside of a glass tube. It is a guarantee that the tube has good vacuum. If the seal on the tube fails, the getter flash will turn white (because it turns into barium oxide)." If I understand that, then that means that tube is bad and the other three are good. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 If this is the case, shouldn`t I notice something sound wise? This 60wpc 55lb beast is loud, quick, tight and quiet in all the right places. This amp does get warm which is why it is supplied with a small fan on the left hand side of the amp that pulls cool air across the tubes. Could it be this is why the right side looks like they have gotten hotter? Maybe my ear doesn`t know what to listen for here. If a power tube is out will that just affect the power to one channel or both? Also, if I did need a new KT88 do I just replace the one or do I get a matched set? At this point I think I`ll wait until I hear a reason to change it out. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted May 31, 2004 Author Share Posted May 31, 2004 Well I just put my new tube toy in triode mode. And guess what? The intermittent high pitch tone resurfaced. Could this mean I need to change the 12au7`s after all? I think that is the logical next step here. Colin. The amp is from `97. The power tubes? I don`t know if they are original. I do know that one or more of the smaller tubes are not original. Hell, the power tubes may not be original either. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted May 31, 2004 Share Posted May 31, 2004 "If I understand that, then that means that tube is bad and the other three are good." Chops, They mean that the getter will become a milky opague white if the seal fails suddenly. If that happens the tube is suddenly dead. What's happening to that KT88(?) in Greg's Rogue is the getter is slowly being used up. Like any other tube it could last for years or fail tomorrow. Greg, It might be time to look for a spare set of outputs or a new set and use the one's you have for back-ups. Then you can have some more fun!! Rick Quote Link to comment Share on other sites More sharing options...
chops Posted May 31, 2004 Share Posted May 31, 2004 ---------------- On 5/31/2004 8:31:52 PM 3dzapper wrote: "If I understand that, then that means that tube is bad and the other three are good." Chops, They mean that the getter will become a milky opague white if the seal fails suddenly. If that happens the tube is suddenly dead. What's happening to that KT88(?) in Greg's Rogue is the getter is slowly being used up. Like any other tube it could last for years or fail tomorrow. Greg, It might be time to look for a spare set of outputs or a new set and use the one's you have for back-ups. Then you can have some more fun!! Rick ---------------- Thanks! I'm still learning here and I just wanted to make sure that someone else would come in here and clear things up a bit. I can honestly say though, within the last couple of weeks, I have learned a lot about tubes and how they work. I can only keep learning. Quote Link to comment Share on other sites More sharing options...
middlecreekguy Posted June 2, 2004 Author Share Posted June 2, 2004 Thanks for all your feedback Chops, Rick and Colin. I`m still playing around with this thing. Listened to it tonight for a side of "The Modern Jazz Quartet" in triode mode. No issues that I heard since changing the 12au7a`s out. Should I have changed just one tube at a time instead of all 4? I wanted to get to the heart of the matter. Now. Quote Link to comment Share on other sites More sharing options...
chops Posted June 2, 2004 Share Posted June 2, 2004 It seems best to replace all four at the same time, that way you will have a matched quad set in there and not "mix and match" sets. Oh yeah, and you're welcome! Quote Link to comment Share on other sites More sharing options...
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