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Post by dei305 on May 25, 2006 12:54:31 GMT -7
Hey guys, Has any had the chance to compare GT vs JJ EL-84's? Which brand is the tonal choice for a MAZ18 jr or MAZ 38 Sr with verb? thanks! Rick
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Post by Paul (TRANE) on May 25, 2006 12:58:39 GMT -7
The stock GT-EL84S used by Dr. Z is a JJ EL-84. So they should be the same.
Paul
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Post by Paul (TRANE) on May 25, 2006 13:09:54 GMT -7
If you go up to www.guitaramplifierblueprinting.com there is lots of info there including what each type of groove tube is. That is you get the groove tube name and the original mfg's name for it. Pretty cool. One thing that you will gain from GT is that the tubes are dynamically balanced....not just static balanced. This can make a big difference in performance/tone. So not only will you get a JJ set you will get an extremely well matched JJ set.
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Post by dei305 on May 25, 2006 13:19:17 GMT -7
Trane, Thanks so much..+1 karma for ya!
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Post by Paul (TRANE) on May 25, 2006 13:38:37 GMT -7
No problem. Thanks for the karma.
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Post by bustertheboy on May 25, 2006 14:22:41 GMT -7
i've tried both the GT and the JJ in both my ghia and my son's boogie- both are really good, but the GT s seemed a little punchier/ maybe louder, and unless i'm imagining it, had a bit more sparkle
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Post by myles on May 25, 2006 16:13:26 GMT -7
They are the same tube but the GT is tested differently and graded as to where the tube distorts for a given rating number. They are also dynamically matched rather than statically matched.
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Post by dei305 on May 25, 2006 20:03:35 GMT -7
Myles, Thanks! Rick
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Post by ke4unr on May 26, 2006 12:51:56 GMT -7
They are the same tube but the GT is tested differently and graded as to where the tube distorts for a given rating number. They are also dynamically matched rather than statically matched. Hi Myles, Maybe you just answered this and I didn't know enough to understand... My 3 week old Maz Jr came with the GT EL84S #6. I just happened to pull the duet two nights ago and put them on my Hickok 750 tube tester while I was measuring other tubes. They did not match. Not way off, but not close either. I have a Peavey Classic 30 loaded with JJ's. I pulled the quartet of EL84's out, measured them to make sure. Yep, they all matched. So I put a couple in my Maz. Seemed to sound better to my ears. I realize other criteria may need to be applied. I don't have access to a curve tracer, O'scope, VTV or the like. Am I safe to assume that what I measured on my mutual conductance tester is good/close enough to be accurate? I've never used GT tubes before and want to make sure I'm not overlooking some other characteristics, as I'm also not used to the Grading scheme. Thanks, Ray K.
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Post by myles on May 27, 2006 18:38:43 GMT -7
They are the same tube but the GT is tested differently and graded as to where the tube distorts for a given rating number. They are also dynamically matched rather than statically matched. Hi Myles, Maybe you just answered this and I didn't know enough to understand... My 3 week old Maz Jr came with the GT EL84S #6. I just happened to pull the duet two nights ago and put them on my Hickok 750 tube tester while I was measuring other tubes. They did not match. Not way off, but not close either. I have a Peavey Classic 30 loaded with JJ's. I pulled the quartet of EL84's out, measured them to make sure. Yep, they all matched. So I put a couple in my Maz. Seemed to sound better to my ears. I realize other criteria may need to be applied. I don't have access to a curve tracer, O'scope, VTV or the like. Am I safe to assume that what I measured on my mutual conductance tester is good/close enough to be accurate? I've never used GT tubes before and want to make sure I'm not overlooking some other characteristics, as I'm also not used to the Grading scheme. Thanks, Ray K. Ray, Unfortunately, tube tester from the past cannot develop proper voltages for ourput tubes. They are great for preamp tubes though. The readings on output tubes have little value and are not really accurate as the tube is not being pushed as it would be in a guitar amp. But .... there is a tester called the Maxi-Matcher that does develop proper voltages and is a good way to static match tubes. If the static match was within 10-15% you would be fine and you would find on a dynamic match (if the tubes had not been mishandled) they would trace exactly. Mutual transconductance is also not a good way to measure output tubes. You want to measure current output in milliamps. A good spec EL84 at 325 plate volts with a -7.3 volt bias should read 48mA.
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Post by ke4unr on May 29, 2006 14:16:58 GMT -7
Ray, Unfortunately, tube tester from the past cannot develop proper voltages for ourput tubes. They are great for preamp tubes though. The readings on output tubes have little value and are not really accurate as the tube is not being pushed as it would be in a guitar amp. But .... there is a tester called the Maxi-Matcher that does develop proper voltages and is a good way to static match tubes. If the static match was within 10-15% you would be fine and you would find on a dynamic match (if the tubes had not been mishandled) they would trace exactly. Mutual transconductance is also not a good way to measure output tubes. You want to measure current output in milliamps. A good spec EL84 at 325 plate volts with a -7.3 volt bias should read 48mA. Myles, Thanks for the explanation and great info! I've never used one, but I am familiar with the Maxi-Matcher... and it's price. That's the only reason I don't own one. I used to check tubes in my amps for current output without having to pull the chassis. Using a couple of methods. Btw, these were fixed biased amps, where I already knew that value. First, I would clip a small insulated test clip to the plate pin and install the tube. It wouldn't be flush to the socket, but enough that all pins were making good contact. The other end of that clip would go to the positive lead of my digital multimeter. The negative lead would go to chassis ground. With the amp powered and warmed up, I could get the plate measured in volts DC. I was too curious, so I just went and did this. Measuring both JJ and GT branded tubes. I read 340 plate volts on each. So, once this is known I would look up the standard plate dissipation for the particular tube. If not supplied by the manufacturer, then in my trusty RCA manual. With these known values I could do some simple calculations to determine the approximate current output in milliamps. Standard plate dissipation/Plate volts = Current output in milliamps. Then I'd multiply that value by .75. An EL84 has a standard dissipation of 12 watts. So just for fun, using the values I have, it would look something like this: 12 watts/340 pv = .035 = 35 ma .037 ma x .75 = .026 = 26 ma The .75 being 75% which should be just out of crossover distortion. The two values would give me a "safe" range to work with. Tubes toward the higher value should have a "warmer" tone and vice-versa. But, I must be missing something (it has been awhile!), as I'm getting nowhere near 48ma. So, I took a peek at my RCA manual and it shows plate voltage for a 6BQ5 as 250 volts. Plugging that number in, I now get 48ma to 36 ma as an acceptable range. But, to make things easier on myself, I built a long time ago a dual digital readout bias checker using socket adapters similar to what GT and others now offer. What I have right now will only work with Octal tubes though, so I need to build up some mini 9-pin adapters if I intend to use it with my Maz Jr. Until then, I won't be able to get a true milliamp measurement for the tubes. So, to sum up for now, since the plate voltage for the tubes I measured are 340 volts the output current should be right at 35 ma. Below the 48 ma you recommend. What grade GT EL84's would you suggest going to, Myles? Sorry for the wordy reply, I'm just trying to understand this. Btw, I have no complaints. My ears tell me the amp sounds great. I just want to make sure I'm getting all I can out of it. Thanks, Ray K.
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Post by myles on May 30, 2006 8:24:43 GMT -7
Ray, Unfortunately, tube tester from the past cannot develop proper voltages for ourput tubes. They are great for preamp tubes though. The readings on output tubes have little value and are not really accurate as the tube is not being pushed as it would be in a guitar amp. But .... there is a tester called the Maxi-Matcher that does develop proper voltages and is a good way to static match tubes. If the static match was within 10-15% you would be fine and you would find on a dynamic match (if the tubes had not been mishandled) they would trace exactly. Mutual transconductance is also not a good way to measure output tubes. You want to measure current output in milliamps. A good spec EL84 at 325 plate volts with a -7.3 volt bias should read 48mA. Myles, Thanks for the explanation and great info! I've never used one, but I am familiar with the Maxi-Matcher... and it's price. That's the only reason I don't own one. I used to check tubes in my amps for current output without having to pull the chassis. Using a couple of methods. Btw, these were fixed biased amps, where I already knew that value. First, I would clip a small insulated test clip to the plate pin and install the tube. It wouldn't be flush to the socket, but enough that all pins were making good contact. The other end of that clip would go to the positive lead of my digital multimeter. The negative lead would go to chassis ground. With the amp powered and warmed up, I could get the plate measured in volts DC. I was too curious, so I just went and did this. Measuring both JJ and GT branded tubes. I read 340 plate volts on each. So, once this is known I would look up the standard plate dissipation for the particular tube. If not supplied by the manufacturer, then in my trusty RCA manual. With these known values I could do some simple calculations to determine the approximate current output in milliamps. Standard plate dissipation/Plate volts = Current output in milliamps. Then I'd multiply that value by .75. An EL84 has a standard dissipation of 12 watts. So just for fun, using the values I have, it would look something like this: 12 watts/340 pv = .035 = 35 ma .037 ma x .75 = .026 = 26 ma The .75 being 75% which should be just out of crossover distortion. The two values would give me a "safe" range to work with. Tubes toward the higher value should have a "warmer" tone and vice-versa. But, I must be missing something (it has been awhile!), as I'm getting nowhere near 48ma. So, I took a peek at my RCA manual and it shows plate voltage for a 6BQ5 as 250 volts. Plugging that number in, I now get 48ma to 36 ma as an acceptable range. But, to make things easier on myself, I built a long time ago a dual digital readout bias checker using socket adapters similar to what GT and others now offer. What I have right now will only work with Octal tubes though, so I need to build up some mini 9-pin adapters if I intend to use it with my Maz Jr. Until then, I won't be able to get a true milliamp measurement for the tubes. So, to sum up for now, since the plate voltage for the tubes I measured are 340 volts the output current should be right at 35 ma. Below the 48 ma you recommend. What grade GT EL84's would you suggest going to, Myles? Sorry for the wordy reply, I'm just trying to understand this. Btw, I have no complaints. My ears tell me the amp sounds great. I just want to make sure I'm getting all I can out of it. Thanks, Ray K. Ray, On cathode biased amps I actually run idle at 100% rather than your 75% value ... and even up to 120% in some cases. Yup ... hot! Also, the JJ EL84 actually handles 14 watts with ease even though it is rated at 12 watts.
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Post by ke4unr on May 30, 2006 14:55:18 GMT -7
Ray, On cathode biased amps I actually run idle at 100% rather than your 75% value ... and even up to 120% in some cases. Yup ... hot! Also, the JJ EL84 actually handles 14 watts with ease even though it is rated at 12 watts. Hi Myles, Oh, I don't run mine at 75% either! Sorry for the misunderstanding. If my GT-EL84-S #6 duet and my JJ EL84 quartet all measure 340 plate volts in the amp, I calculate that as 35ma plate current, assuming the 12 volts standard dissipation. Good so far? Since that is less than the 48ma that I thought you were recommending, which grade of GT tubes would I need? I read as much as I could but still do not understand the grading system completely. At least I can't find where to equate the current output to the grade number. Sorry if I've overlooked it. I also need to get off my duff and either build or buy some mini 9-pin probes, so I can get accurate measurements with the tubes under load in the amp. Thanks, Ray K.
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Post by myles on May 30, 2006 15:03:21 GMT -7
Ray, On cathode biased amps I actually run idle at 100% rather than your 75% value ... and even up to 120% in some cases. Yup ... hot! Also, the JJ EL84 actually handles 14 watts with ease even though it is rated at 12 watts. Hi Myles, Oh, I don't run mine at 75% either! Sorry for the misunderstanding. If my GT-EL84-S #6 duet and my JJ EL84 quartet all measure 340 plate volts in the amp, I calculate that as 35ma plate current, assuming the 12 volts standard dissipation. Good so far? Since that is less than the 48ma that I thought you were recommending, which grade of GT tubes would I need? I read as much as I could but still do not understand the grading system completely. At least I can't find where to equate the current output to the grade number. Sorry if I've overlooked it. I also need to get off my duff and either build or buy some mini 9-pin probes, so I can get accurate measurements with the tubes under load in the amp. Thanks, Ray K. Ray, Your math is right on the money. basically the 48mA is on a lab standard tube at 250 plate volts with a -7.3 volt bias. As far as rating vs current, it really does not equate. But .... a mid range tube like a 5-6 will generally be on spec or very close, that is .... a #5 at 250 plate volts with that -7.3 volt bias will put out about 48 milliamps. Keeping the voltages the same and going to say a #8 we would see 56mA or more. This is how I bias fixed bias amps actually such as Mesa Boogie or Hiwatts ... go up or down in rating to get the bias I want.
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Post by ke4unr on May 31, 2006 6:09:54 GMT -7
Your math is right on the money. Great! I don't get that too often... Myles, Ok, thanks for the explanation/education. I understand know and much appreciate your help, and patience. +1 for you, my friend. Thanks, Ray K.
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Post by myles on May 31, 2006 9:24:02 GMT -7
Your math is right on the money. Great! I don't get that too often... Myles, Ok, thanks for the explanation/education. I understand know and much appreciate your help, and patience. +1 for you, my friend. Thanks, Ray K. Ray, You are quite welcome
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Post by dei305 on Jun 3, 2006 9:08:18 GMT -7
Myles, Just a quick heads up on my original question : GT vs JJ EL-84's. I had the good doctor perform some surgery on my MAZ Invasion. He suggested re-tubing the amp as well. I have to tell the Gt's sound wonderful. I am hearing a bit more richness compared to the JJ's. So, just wanted to say thanks and also include +1 karma for you! Rick
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Post by myles on Jun 4, 2006 12:19:56 GMT -7
Myles, Just a quick heads up on my original question : GT vs JJ EL-84's. I had the good doctor perform some surgery on my MAZ Invasion. He suggested re-tubing the amp as well. I have to tell the Gt's sound wonderful. I am hearing a bit more richness compared to the JJ's. So, just wanted to say thanks and also include +1 karma for you! Rick Rick, Thanks for the compliment It is probably just a factor of the GT stuff being dynamically matched across the entire range of the tube rather than just statically matched at idle.
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