Members 1tallbassguy Posted July 15, 2008 Members Share Posted July 15, 2008 I replaced the tube with an Electro Harmonix. The one that was in there was a Unison Research 12AU7. I guess those are the ones made in Italy. Oh this is on the amp I picked up yesterday a MusicMan HD-500, which btw was made by Markbass. OOh it is schweet! I'll get some pics up in a bit...I know the rules. It gets a really warm sound. Very tubelike tones from this amp. It uses IGBT's which has some characteristics of a mosfet and some of a typical transister...so I've read:blah: Anyway is there any reason why I should not keep the 12AX7 in and put the 12AU7 back in? Link to comment Share on other sites More sharing options...
Members misterhinkydink Posted July 15, 2008 Members Share Posted July 15, 2008 If you like it, keep it. Link to comment Share on other sites More sharing options...
Members Decker Posted July 16, 2008 Members Share Posted July 16, 2008 Well, the 12au7 has a gain (meaning the amplification factor) of about 20 and the theoretical gain of a 12ax7 is 100, so you may be overloading the stage after the tube. The cathode resistors that are biasing the triode sections of the original 12au7 are probably not optimal for the 12ax7, so it may be running at a bias that is too much for it. 12au7s can be run at a much higher current than 12ax7s. Consequently, the 12ax7 might burn out much sooner. Lucky for you, all the members of the 12__7 family (12au7, gain of 20; 12at7, gain of 40; 12ay7, gain of 60?; 5751, gain of 70; 12ax7, gain of 100) have the same pin out, otherwise you might have damaged your amp. Before substituting tubes, you have to make sure that the pins of each are attached to identical structures within the tube. If you like the difference in the sound that the 12ax7 gives, try the 12at7, which has higher gain than the 12au7 and is typically run at a much higher current than the 12ax7. Link to comment Share on other sites More sharing options...
Members Renfield Posted July 16, 2008 Members Share Posted July 16, 2008 Well, the 12au7 has a gain (meaning the amplification factor) of about 20 and the theoretical gain of a 12ax7 is 100, so you may be overloading the stage after the tube. The cathode resistors that are biasing the triode sections of the original 12au7 are probably not optimal for the 12ax7, so it may be running at a bias that is too much for it. 12au7s can be run at a much higher current than 12ax7s. Consequently, the 12ax7 might burn out much sooner. Lucky for you, all the members of the 12__7 family (12au7, gain of 20; 12at7, gain of 40; 12ay7, gain of 60?; 5751, gain of 70; 12ax7, gain of 100) have the same pin out, otherwise you might have damaged your amp. Before substituting tubes, you have to make sure that the pins of each are attached to identical structures within the tube. If you like the difference in the sound that the 12ax7 gives, try the 12at7, which has higher gain than the 12au7 and is typically run at a much higher current than the 12ax7. What he said. Link to comment Share on other sites More sharing options...
Members 1tallbassguy Posted July 16, 2008 Author Members Share Posted July 16, 2008 Well, the 12au7 has a gain (meaning the amplification factor) of about 20 and the theoretical gain of a 12ax7 is 100, so you may be overloading the stage after the tube. The cathode resistors that are biasing the triode sections of the original 12au7 are probably not optimal for the 12ax7, so it may be running at a bias that is too much for it. 12au7s can be run at a much higher current than 12ax7s. Consequently, the 12ax7 might burn out much sooner. Lucky for you, all the members of the 12__7 family (12au7, gain of 20; 12at7, gain of 40; 12ay7, gain of 60?; 5751, gain of 70; 12ax7, gain of 100) have the same pin out, otherwise you might have damaged your amp. Before substituting tubes, you have to make sure that the pins of each are attached to identical structures within the tube. If you like the difference in the sound that the 12ax7 gives, try the 12at7, which has higher gain than the 12au7 and is typically run at a much higher current than the 12ax7. Thanks man that helps. I knew there was a science to it. Link to comment Share on other sites More sharing options...
Members bassman1956 Posted July 16, 2008 Members Share Posted July 16, 2008 Here's a tube gain chart... Link to comment Share on other sites More sharing options...
Members Decker Posted July 16, 2008 Members Share Posted July 16, 2008 Oops, my bad. I got the 12at7 and 12ay7 reversed. Just goes to show, check it before plugging it in. Link to comment Share on other sites More sharing options...
Members 1tallbassguy Posted July 16, 2008 Author Members Share Posted July 16, 2008 Oops, my bad. I got the 12at7 and 12ay7 reversed. Just goes to show, check it before plugging it in. Thats alright. I went ahead and replaced the 12AU7, and ordered a couple more to have as backups. I'll just stick with the 12AU7 since that is what it is designed for. Link to comment Share on other sites More sharing options...
Members 1tallbassguy Posted July 16, 2008 Author Members Share Posted July 16, 2008 Oops, my bad. I got the 12at7 and 12ay7 reversed. Just goes to show, check it before plugging it in. Oh and according to that chart, the 12AV7 is compatible with the 12AU7.:poke: Link to comment Share on other sites More sharing options...
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