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#1
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ebay sellers response to 5751 ? true ?
Description:
Pair of NIB GE JG-5751 triple mica black plate military tubes.Test 1250/1325 and 1450/1450 where new/nominal is 1250 gm and minimum is 812 on calib. Hickok 533A tester. Question: 5751 being mil spec do you have an idea why they would test so differently? Answer: Yeah I do: Mil-spec doesn't imply matched sections, in fact it doesn't really imply anything. The 5751 is less noisy and microphonic than a AX7. You should really understand that you couldn't hear a difference betwen tubes that were say 950gm and 1500gm. Just the result of tube dealers trying to one up each other etc.. mostly a bunch of crap. Theoretically you want tubes relatively close in gm so they get used at the same rate and last as long as possible, but it's not reality. They NEVER wear evenly, so again it's just BS. Perhaps you can enlighten some others in your situation of these realities. BTW: those tubes test about as good as they get 1250 is high, sometimes new 5751's only test 1100, so those should last as long as anything if you follow, (or have the probability of doing so. Reply: Your detailed response debunking some of the myths surrounding tubes is very much appreciated. I will keep an eye on your auction and place a bid if I can afford to. Thanks |
#2
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I have no problem with what this seller says.
I would, at this point, be far more interested in the getter flashing size and appearance than the Gm for these particular examples for establishing "new-ness". also, the guy that perhaps knows more than anyone on tubes for guitars (probably even more than myself or uncle Ned!), R.G. Keen, gives technical reasons why, in fact, you want tube sections to NOT match! read his TUBE FAQ at http://www.geofex.com/tubeampfaq/TUBEFAQ.htm cheers! cowboy "Ozzy 2005" wrote in message ... Description: Pair of NIB GE JG-5751 triple mica black plate military tubes.Test 1250/1325 and 1450/1450 where new/nominal is 1250 gm and minimum is 812 on calib. Hickok 533A tester. Question: 5751 being mil spec do you have an idea why they would test so differently? Answer: Yeah I do: Mil-spec doesn't imply matched sections, in fact it doesn't really imply anything. The 5751 is less noisy and microphonic than a AX7. You should really understand that you couldn't hear a difference betwen tubes that were say 950gm and 1500gm. Just the result of tube dealers trying to one up each other etc.. mostly a bunch of crap. Theoretically you want tubes relatively close in gm so they get used at the same rate and last as long as possible, but it's not reality. They NEVER wear evenly, so again it's just BS. Perhaps you can enlighten some others in your situation of these realities. BTW: those tubes test about as good as they get 1250 is high, sometimes new 5751's only test 1100, so those should last as long as anything if you follow, (or have the probability of doing so. Reply: Your detailed response debunking some of the myths surrounding tubes is very much appreciated. I will keep an eye on your auction and place a bid if I can afford to. Thanks |
#3
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"Ozzy 2005" wrote in message
... Description: Pair of NIB GE JG-5751 triple mica black plate military tubes.Test 1250/1325 and 1450/1450 where new/nominal is 1250 gm and minimum is 812 on calib. Hickok 533A tester. Question: 5751 being mil spec do you have an idea why they would test so differently? They seem to test Damn close for transconductance to me. Answer: Yeah I do: Mil-spec doesn't imply matched sections, in fact it doesn't really imply anything. The 5751 is less noisy and microphonic than a AX7. Exept that a 5751 is not a 12AX7, the 5751 has less gain by some 30% You should really understand that you couldn't hear a difference betwen tubes that were say 950gm and 1500gm. This is a True statement Just the result of tube dealers trying to one up each other etc.. mostly a bunch of crap. Theoretically you want tubes relatively close in gm so they get used at the same rate and last as long as possible, but it's not reality. They NEVER wear evenly, so again it's just BS. Tubes do not wear out in a linear fashion. A well used tube will test near nominal for most of its life. When the emmisssive coating is depleted from the cathode the tube in question will then rapidly drop in transconductance. Perhaps you can enlighten some others in your situation of these realities. BTW: those tubes test about as good as they get 1250 is high, sometimes new 5751's only test 1100, so those should last as long as anything if you follow, (or have the probability of doing so. I have NOS 12AX7 tubes that tested significantly below nominal right out of the box. The same tubes are still in use, 5000 to 7000 hrs later, testing right where they tested out of the box Transconductance is a very poor indicator of a vacuum tubes "newness". Most tube testers transconductance (or emission) test cannot be used to judge the "match" of pairs or sections of tubes (yes, there are expetions but I am willing to bet you or the seller don't own such a tester) They don't test a tube even remotely close to normal operating conditions. Only making a mesurement of current while the tube is in actual "in circuit" use, passing an actual real world signal, will match up pairs reliablely. The REALLY IMPORTANT tests a tube tester performs are the shorts and inter-element leakage tests. A tube with a short can put an end to your equipment in an instant. Reply: Your detailed response debunking some of the myths surrounding tubes is very much appreciated. I will keep an eye on your auction and place a bid if I can afford to. Thanks A tube tester is a quick-N-dirty way of checking a tube for basic functions. Most are not accurate current matching devices or accurate gauges of how NOS a particular tube is. Service testers like most Hikkoks, Sencores, B&Ks and so forth are tools to weed out bad, shorted or worn out tubes in a service call situation. If you want to match tubes, buy and learn to use a curve tracer or build your own. -- Alan Gallacher Born to Tinker! |
#4
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cowboy wrote:
I have no problem with what this seller says. I would, at this point, be far more interested in the getter flashing size and appearance than the Gm for these particular examples for establishing "new-ness". also, the guy that perhaps knows more than anyone on tubes for guitars (probably even more than myself or uncle Ned!), R.G. Keen, gives technical reasons why, in fact, you want tube sections to NOT match! read his TUBE FAQ at http://www.geofex.com/tubeampfaq/TUBEFAQ.htm cheers! cowboy "Ozzy 2005" wrote in message ... Description: Pair of NIB GE JG-5751 triple mica black plate military tubes.Test 1250/1325 and 1450/1450 where new/nominal is 1250 gm and minimum is 812 on calib. Hickok 533A tester. Question: 5751 being mil spec do you have an idea why they would test so differently? Answer: Yeah I do: Mil-spec doesn't imply matched sections, in fact it doesn't really imply anything. The 5751 is less noisy and microphonic than a AX7. You should really understand that you couldn't hear a difference betwen tubes that were say 950gm and 1500gm. Just the result of tube dealers trying to one up each other etc.. mostly a bunch of crap. Theoretically you want tubes relatively close in gm so they get used at the same rate and last as long as possible, but it's not reality. They NEVER wear evenly, so again it's just BS. Perhaps you can enlighten some others in your situation of these realities. BTW: those tubes test about as good as they get 1250 is high, sometimes new 5751's only test 1100, so those should last as long as anything if you follow, (or have the probability of doing so. Reply: Your detailed response debunking some of the myths surrounding tubes is very much appreciated. I will keep an eye on your auction and place a bid if I can afford to. Thanks I just finished reading all of it - much thanks. |
#5
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Anumber1 wrote:
"Ozzy 2005" wrote in message ... Description: Pair of NIB GE JG-5751 triple mica black plate military tubes.Test 1250/1325 and 1450/1450 where new/nominal is 1250 gm and minimum is 812 on calib. Hickok 533A tester. Question: 5751 being mil spec do you have an idea why they would test so differently? They seem to test Damn close for transconductance to me. Answer: Yeah I do: Mil-spec doesn't imply matched sections, in fact it doesn't really imply anything. The 5751 is less noisy and microphonic than a AX7. Exept that a 5751 is not a 12AX7, the 5751 has less gain by some 30% You should really understand that you couldn't hear a difference betwen tubes that were say 950gm and 1500gm. This is a True statement Just the result of tube dealers trying to one up each other etc.. mostly a bunch of crap. Theoretically you want tubes relatively close in gm so they get used at the same rate and last as long as possible, but it's not reality. They NEVER wear evenly, so again it's just BS. Tubes do not wear out in a linear fashion. A well used tube will test near nominal for most of its life. When the emmisssive coating is depleted from the cathode the tube in question will then rapidly drop in transconductance. Perhaps you can enlighten some others in your situation of these realities. BTW: those tubes test about as good as they get 1250 is high, sometimes new 5751's only test 1100, so those should last as long as anything if you follow, (or have the probability of doing so. I have NOS 12AX7 tubes that tested significantly below nominal right out of the box. The same tubes are still in use, 5000 to 7000 hrs later, testing right where they tested out of the box Transconductance is a very poor indicator of a vacuum tubes "newness". Most tube testers transconductance (or emission) test cannot be used to judge the "match" of pairs or sections of tubes (yes, there are expetions but I am willing to bet you or the seller don't own such a tester) They don't test a tube even remotely close to normal operating conditions. Only making a mesurement of current while the tube is in actual "in circuit" use, passing an actual real world signal, will match up pairs reliablely. The REALLY IMPORTANT tests a tube tester performs are the shorts and inter-element leakage tests. A tube with a short can put an end to your equipment in an instant. Reply: Your detailed response debunking some of the myths surrounding tubes is very much appreciated. I will keep an eye on your auction and place a bid if I can afford to. Thanks A tube tester is a quick-N-dirty way of checking a tube for basic functions. Most are not accurate current matching devices or accurate gauges of how NOS a particular tube is. Service testers like most Hikkoks, Sencores, B&Ks and so forth are tools to weed out bad, shorted or worn out tubes in a service call situation. If you want to match tubes, buy and learn to use a curve tracer or build your own. gotcha thanks |
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