DC Ross Posted January 12, 2006 Share Posted January 12, 2006 Hey guys, I posted this question over on the bass forum , but since it applies here as well... Is there a simple way to test power tubes (without taking it to a tech) to determine if they need to be replaced? Thanks! -DC Ross It's not simple to be simple. -H. Matisse Ross Precision Guitars Link to comment Share on other sites More sharing options...
Corner Pocket Posted January 12, 2006 Share Posted January 12, 2006 What kind of amp? In my Fender Twin, if it sounds good, the tubes are good. If it sounds bad, it's time to figure out if there is a tube problem. Step one: Is it the power tubes? Remove the phase inverter tube, and tap on the power tubes, If you get horrible noises, there is a power tube problem. Time to replace tubes and reset bias. Step two: Is it a pre amp tube problem? Pull all pre-tubes except the phase inverter tube. Using the V1 position, test all pre-amp tubes one at a time. Let them heat up. It usually takes 10 minutes per tube to find out if the tube is a problem. Run the amp full up, (you don't need a guitar plugged in) and flick away at the tube. Try to make it squeall or buzz or complain No horrible noises means tube is good, time to move on and try the others. That's how I isolate a bad tube in a Fender Twin Reverb with a phase inverter tube. This won't work for all amps. Paul Peace, Paul ---------------------- Link to comment Share on other sites More sharing options...
miroslav Posted January 12, 2006 Share Posted January 12, 2006 Well OK...if all you are testing for is microphonics...then the tap-on-the-tubes trick will give you some hints. But...that tells you NOTHING about the actual mutual transconductance/GM values...which are one of the main specs for checking if a tube is good/bad. Then there is Emissions...then Shorts... ...and finally, some tubes need to be checked for balance, which is most important for the inverters, since you want both sides to be about even. For all of that...you need proper tube testers. You can get decent EM/GM tester on eBay for about $150-$300. I have a Precise 111 which is quite versatile and accurate. I'm sure Myles can give you even more details on how to properly test tubes. miroslav - miroslavmusic.com "Just because it happened to you, it doesn't mean it's important." Link to comment Share on other sites More sharing options...
miroslav Posted January 12, 2006 Share Posted January 12, 2006 miroslav - miroslavmusic.com "Just because it happened to you, it doesn't mean it's important." Link to comment Share on other sites More sharing options...
Ricochet Posted January 12, 2006 Share Posted January 12, 2006 Tube testers have always been problematic. There are several types that test different things, mainly emission testers and the mutual conductance testers of several different types. The big problem is that none of them can really predict whether a tube will function properly in the equipment. Tube testers as we recall them from the days of tube TVs and radios (mainly emission testers) were primarily popularized to sell more tubes to people whose tubes were still working fine but showed "weak" on the emission gauge. I agree with the above statement that "if it sounds good, the tubes are good." The best test for whether a tube is causing a problem remains substitution of a known-good tube. "A cheerful heart is good medicine." Link to comment Share on other sites More sharing options...
miroslav Posted January 12, 2006 Share Posted January 12, 2006 OK...but...how do you know if you have a "known good tube"...??? By using a good tube tester! I've seen BRAND NEW tubes of current manufacture that crap out...or that had HUGE differences in GM values from tube to tube. So while it may sound good...it may also not last too long or be "good enough". Also...if you like to purchase NOS or used vintage tubes...then you really have NO WAY of knowing if it is a "known good tube"...until you at least run it through a tube tester. You wanna risk just plugging in a tube the may have a short (which may crap out something else in your circuit)... ...then go for it! Once I stated expanding my tube gear collection...I then decided I wanted to have a bunch of different tubes on hand for all that gear... ...and then I also realized that a good tube tester was not a bad thing to have around! There is plenty of garbage out there...but if you look around...you can still score a solid working tester for a couple hundred bucks... ...and it will last you probably the rest of your lifetime. But...if you only swap tubes in one amp...once in a blue moon... ...then just take it to the shop, and let them test/swap the tubes for you. Once you take some readings with a tester... What would your rather put in your amp...a tube that had high GM/EM readings and NO shorts... ...or a tube that had low readings and possible shorts...? Huh...? I thought so! But how are you going to know which is which tube... .unless you have a tester! miroslav - miroslavmusic.com "Just because it happened to you, it doesn't mean it's important." Link to comment Share on other sites More sharing options...
Guitar Geezer Posted January 12, 2006 Share Posted January 12, 2006 Remember when they had tube testers in every 7-11? That's right, you guys ain't that old Lynn G Link to comment Share on other sites More sharing options...
Ricochet Posted January 12, 2006 Share Posted January 12, 2006 Well, really the way you identify a "known good tube" is by seeing if it works. I've got a couple of tube testers myself, and I do use them, but am aware of their limitations. A tube tester's not an essential piece of equipment for servicing amps. As for brand new tubes of current manufacture "crapping out" or arriving defective, I saw plenty of faulty new ones in the early 1960s, of all the good old American makes being praised to the heavens as NOS now. They were no better. And the first couple of hundred hours of operation is when most tubes that fail do so. If they make it past that, they'll likely gradually fade away from emission loss after a long and happy life, which is why it doesn't make much sense to periodically replace working tubes as "preventive maintenance." You're increasing your risk of a tube going out that way. "A cheerful heart is good medicine." Link to comment Share on other sites More sharing options...
Ricochet Posted January 12, 2006 Share Posted January 12, 2006 Hey Geezer, we had tube testers all over the place, but 7-11s hadn't arrived on the scene yet. "A cheerful heart is good medicine." Link to comment Share on other sites More sharing options...
Dusty Chalk Posted January 13, 2006 Share Posted January 13, 2006 Originally posted by Guitar Geezer: Remember when they had tube testers in every 7-11? That's right, you guys ain't that old Radio Shack, yes; 7-11, no. I remain, :-Peter, aka :-Dusty :-(halk Link to comment Share on other sites More sharing options...
DC Ross Posted January 13, 2006 Author Share Posted January 13, 2006 Thanks for the replys; there's bunches of good information here! The amp is a Mesa/Boogie Bass 400(the original, not the new "+" model) with 6 6L6 power tubes. I bought the amp used about a year and a half ago, and it was manufactured in 1985. I have no idea how old the tubes are. I'm guessing they're old, but not original. The current is written on each of the tubes which helps, since it's a fixed bias amp. Unfortunately, I have no idea what preamp tube is what, since I can't find any documentation on line. The instruction manual for the new Bass 400+ (similar but different - 12 power tubes) doesn't have any useful information. I was thinking of just picking up a set of TADs or SEDs from The Tube Store and replacing them. Since the bias is fixed, I just need to get tubes with the correct rating, right? Thanks again! It's not simple to be simple. -H. Matisse Ross Precision Guitars Link to comment Share on other sites More sharing options...
miroslav Posted January 13, 2006 Share Posted January 13, 2006 Originally posted by Ricochet: Well, really the way you identify a "known good tube" is by seeing if it works.I know what you are saying..."plug it in, and if it sounds OK, then the tube must be good". Yeah, fine. But answer my question. If you have a couple of "known good tubes" that equally sound OK when you place them into operation... ...but then you take those same two tubes and check their mutual transconductance/GM values, and one of the tubes is reading close to it's minimal operating value... ...and the other is reading well above it... ...be honest... ...which tube would you place back in your amp? And what if you needed a balanced tube, like for the phase inverter...how do you know that both sides of the triode are about equal by just placing it into operation? With a good tester, (like I have)...reading each side gives a pretty solid indication if it is or isn't balanced.though a curve trace is even more accurate for that. I just find your implication that tube testers are waste of time...a bit extreme. And saying that everyone should just plug tubes in, tap on them...and if they "work"... ...that's the best way to tell if they are good....??? I use a Precise 111...here's some info on it, showing that it's not your average tester. http://www.tone-lizard.com/Precise111.htm But there are many testers that don't give you anything more than either a "Good" or "Bad" scale to go by...and using any of those testers...well, then you might as well just stick the tube into operation and "test" it that way! miroslav - miroslavmusic.com "Just because it happened to you, it doesn't mean it's important." Link to comment Share on other sites More sharing options...
Ricochet Posted January 13, 2006 Share Posted January 13, 2006 Miroslav, either one would work. I don't give a damn what the tester says about their respective Gm values. I don't give a rat whether they're "balanced." If the amp sounds good, it is good. "A cheerful heart is good medicine." Link to comment Share on other sites More sharing options...
miroslav Posted January 14, 2006 Share Posted January 14, 2006 That's fine...do it your way. But I don't just have guitar amps with tubes. I also have mic pres, compressors, and a whole bunch of mics...and I prefer to know the quality and specs of any tube I'm going to stick into that equipment. Then....after I run 'em through the tube tester... ...I too check if they sound good, as the last step. You know...they put car engines through all kinds of tests...with all kinds of equipment. Your way would be to just step on the gas....and if the car moves...then the engine must be good! miroslav - miroslavmusic.com "Just because it happened to you, it doesn't mean it's important." Link to comment Share on other sites More sharing options...
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