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#1
Posted to rec.audio.tubes
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Let's talk about tube amps
I posted a while back about rusty transformers and got lots of response.
It turns out they were rusty because the amp had been ridiculously over heated. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, it still does this but no output tubes were in place as I tested it. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? Any thoughts? |
#2
Posted to rec.audio.tubes
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Let's talk about tube amps
On Fri, 31 Jul 2009 09:20:49 -0600, sortech wrote:
I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. No the were not. heat doesn't make rust, moisture and air do. |
#3
Posted to rec.audio.tubes
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Let's talk about tube amps
PeterD wrote wrote:
I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. No the were not. heat doesn't make rust, moisture and air do. Moisture, oxygen, heat and a voltage or current source do. Overheating may remove surface protection, and repeatedly evaporating condensation from bare steel by heating it can accelerate the rusting process dramatically, especially in the presence of imposed electric currents. Ian |
#4
Posted to rec.audio.tubes
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Let's talk about tube amps
On Jul 31, 4:38*pm, PeterD wrote:
On Fri, 31 Jul 2009 09:20:49 -0600, sortech wrote: I posted a while back about rusty transformers and got lots of response. *It turns out they were rusty because the amp had been ridiculously over heated. No the were not. heat doesn't make rust, moisture and air do. Peter is right, of course. Your amplifier needs a lot more careful tests than the inconsistent forensics you have reported. Take the OPT out of circuit and test with 6.3 VAC on the secondary and measure the ratios P-P and P to center tap. Impedance matching is ratio squared. The power transformer needs similar testing - run 6.3 VAC into the heater winding and measure rectifier P-P and P to centre tap volts. High current in the 6 volt test supply would indicate shorted turns. Then there's all the o/p tube wiring to check... I suggest you let tech do it! Cheers, Roger |
#5
Posted to rec.audio.tubes
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Let's talk about tube amps
"sortech" I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. ** Utter nonsense. The amp has been allowed to get wet - most likely from condensation while in storage. I see that all the time. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, ** No such thing happens. Shorted turns in the primary causes large currents to flow and makes the AC fuse blow. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. ** Sounds about right. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. ** Drivel. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? ** If output tubes get wet during use, the glass often breaks. They break if you hit them hard enough. They break if they bang into each other .... ...... Phil |
#6
Posted to rec.audio.tubes
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Let's talk about tube amps
sortech wrote:
I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. Overheating might have played some part, but damp is the primary culprit. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, In what way does "up and up" differ from "up"? What do you mean by shorted? I can understand that you want to join in with all the fun we have here, so I don't wish to dampen your ardour, but you need to think and write more clearly. Try proper paragraphs. It might be useful, for the purpose of grasping how transformers work, to consider what happens if just some of the primary windings become shorted. Would that lead to an increase in secondary voltage? There is an obvious theoretical reason to think that it might, and a rather more complicated reason, to realise that it most probably won't. The best assumption is that the manufacturer has used as few turns as possible. Your shorted primary hypothesis is not best tested by plugging it into the mains. But it made me think of a nice example of a "reductio ad absurdam". If you continue to short primary turns, then secondary voltage should keep rising because the turns ratio increases. In that case, when you have no turns, then you should have a very high secondary voltage indeed. it still does this but no output tubes were in place as I tested it. Still does what, exactly? HT voltage will normally be higher with valves removed, but by how much depends on the details of the circuit, which few here will be familiar with. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. Likely to be normal. The difference is because the two halves will have the same number of turns, but can't occupy the same space, so one will have a different average coil diameter, and so a different length of wire. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? Any thoughts? Explosions are scarce, I should imagine, although you could have fun thinking up a possible scenario. I wonder how much of the contents would have to vaporise before sufficient positive pressure resulted? Implosions are more likely, because of the vacuum. Ian |
#7
Posted to rec.audio.tubes
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Let's talk about tube amps
"sortech" The amp is a mesa boogie tipple rectifier ... ** The drinking man's favourite model. ...... Phil |
#8
Posted to rec.audio.tubes
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Let's talk about tube amps
"sortech" The amp is a mesa boogie tipple rectifier ** Here is a pic of the Mesa Boogie " Triple Rectifier " : http://img1.iwascoding.de/1/2009/05/...38618CA3BA.jpg No rusty trannys in this one.... ..... Phil |
#9
Posted to rec.audio.tubes
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Let's talk about tube amps
"Ian Iveson" wrote in message ... sortech wrote: I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. Overheating might have played some part, but damp is the primary culprit. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, In what way does "up and up" differ from "up"? What do you mean by shorted? I can understand that you want to join in with all the fun we have here, so I don't wish to dampen your ardour, but you need to think and write more clearly. Try proper paragraphs. It might be useful, for the purpose of grasping how transformers work, to consider what happens if just some of the primary windings become shorted. Would that lead to an increase in secondary voltage? There is an obvious theoretical reason to think that it might, and a rather more complicated reason, to realise that it most probably won't. The best assumption is that the manufacturer has used as few turns as possible. Your shorted primary hypothesis is not best tested by plugging it into the mains. But it made me think of a nice example of a "reductio ad absurdam". If you continue to short primary turns, then secondary voltage should keep rising because the turns ratio increases. In that case, when you have no turns, then you should have a very high secondary voltage indeed. I love it, Ian, the ultimate divide by zero example! Infinite current into the primary; infinite voltage on the secondary! Well done! - Fred it still does this but no output tubes were in place as I tested it. Still does what, exactly? HT voltage will normally be higher with valves removed, but by how much depends on the details of the circuit, which few here will be familiar with. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. Likely to be normal. The difference is because the two halves will have the same number of turns, but can't occupy the same space, so one will have a different average coil diameter, and so a different length of wire. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? Any thoughts? Explosions are scarce, I should imagine, although you could have fun thinking up a possible scenario. I wonder how much of the contents would have to vaporise before sufficient positive pressure resulted? Implosions are more likely, because of the vacuum. Ian |
#10
Posted to rec.audio.tubes
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Let's talk about tube amps
Ian Iveson wrote:
sortech wrote: I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. Overheating might have played some part, but damp is the primary culprit. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, In what way does "up and up" differ from "up"? What do you mean by shorted? I can understand that you want to join in with all the fun we have here, so I don't wish to dampen your ardour, but you need to think and write more clearly. Try proper paragraphs. It might be useful, for the purpose of grasping how transformers work, to consider what happens if just some of the primary windings become shorted. Would that lead to an increase in secondary voltage? There is an obvious theoretical reason to think that it might, and a rather more complicated reason, to realise that it most probably won't. The best assumption is that the manufacturer has used as few turns as possible. Your shorted primary hypothesis is not best tested by plugging it into the mains. But it made me think of a nice example of a "reductio ad absurdam". If you continue to short primary turns, then secondary voltage should keep rising because the turns ratio increases. In that case, when you have no turns, then you should have a very high secondary voltage indeed. it still does this but no output tubes were in place as I tested it. Still does what, exactly? HT voltage will normally be higher with valves removed, but by how much depends on the details of the circuit, which few here will be familiar with. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. Likely to be normal. The difference is because the two halves will have the same number of turns, but can't occupy the same space, so one will have a different average coil diameter, and so a different length of wire. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? Any thoughts? Explosions are scarce, I should imagine, although you could have fun thinking up a possible scenario. I wonder how much of the contents would have to vaporise before sufficient positive pressure resulted? Implosions are more likely, because of the vacuum. Ian I meant that when first powered up the voltage was normal for a low load condition and over a period of a few minutes the voltage increased about 12 percent. The transformer also buzzed more as it warmed and this was the case with a Marshal I repaired a few years ago that needed a power transformer. I checked the line voltage and it was constant at 117 volts. My area has an old power system. So I was thinking only a few windings had shorted before I discontinued the test. The leaking potting material also lead me to think the transformer was likely to be defective. "The drinking man's favourite model." Yes this is the most probable explanation for the glass fragments. Perhaps a collision between power tubes and beer bottle lead to the amps present condition. Is it not likely that a test not using line voltage would not heat the transformer and therefor not show a short? I did fail to provide enough information in my first post but would be pleased to let the blame fall on the US educational system for the sentence structure. Eric |
#11
Posted to rec.audio.tubes
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Let's talk about tube amps
Engineer wrote:
On Jul 31, 4:38 pm, PeterD wrote: On Fri, 31 Jul 2009 09:20:49 -0600, sortech wrote: I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. No the were not. heat doesn't make rust, moisture and air do. Peter is right, of course. Your amplifier needs a lot more careful tests than the inconsistent forensics you have reported. Take the OPT out of circuit and test with 6.3 VAC on the secondary and measure the ratios P-P and P to center tap. Impedance matching is ratio squared. The power transformer needs similar testing - run 6.3 VAC into the heater winding and measure rectifier P-P and P to centre tap volts. High current in the 6 volt test supply would indicate shorted turns. Then there's all the o/p tube wiring to check... I suggest you let tech do it! Cheers, Roger Perhaps, but engineers often come to me. Eric |
#12
Posted to rec.audio.tubes
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Let's talk about tube amps
"sortech" I meant that when first powered up the voltage was normal for a low load condition and over a period of a few minutes the voltage increased about 12 percent. ** Bizzare. Been servicing valve guitar amps for 4 decades and never seen that. Even a few shorted turns blows the AC fuse, real quick. The transformer also buzzed more as it warmed ** Very common for loose laminations to begin to buzz when the tranny warms up. I checked the line voltage and it was constant at 117 volts. My area has an old power system. So I was thinking only a few windings had shorted before I discontinued the test. The leaking potting material also lead me to think the transformer was likely to be defective. ** That last bit indicates a bad tranny. Plus an evil smell and popping /cracking noises as it heats up. "The drinking man's favourite model." Yes this is the most probable explanation for the glass fragments. Perhaps a collision between power tubes and beer bottle lead to the amps present condition. ** The " Triple Rectifier" is famously known as the model played by Saddam Hussein. Even his friends said he sounded like Sheite .... ...... Phil |
#13
Posted to rec.audio.tubes
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Let's talk about tube amps
sortech wrote: I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. NO ! Heat doesn't cause rust in any way or form. Moisture does. Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address |
#14
Posted to rec.audio.tubes
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Let's talk about tube amps
PeterD wrote: On Fri, 31 Jul 2009 09:20:49 -0600, sortech wrote: I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. No the were not. heat doesn't make rust, moisture and air do. I suspect quite a few of these answers. Being left in a warm damp place ( e.g. Florida ) would encourage rust too. Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address |
#15
Posted to rec.audio.tubes
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Let's talk about tube amps
Phil Allison wrote: "sortech" The amp is a mesa boogie tipple rectifier ** Here is a pic of the Mesa Boogie " Triple Rectifier " : http://img1.iwascoding.de/1/2009/05/...38618CA3BA.jpg WTF did they use toob rectifiers for ? To increase the price ? Hype ? Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address |
#16
Posted to rec.audio.tubes
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Let's talk about tube amps
"Eeyore" Phil Allison wrote: "sortech" The amp is a mesa boogie tipple rectifier ** Here is a pic of the Mesa Boogie " Triple Rectifier " : http://img1.iwascoding.de/1/2009/05/...38618CA3BA.jpg WTF did they use toob rectifiers for ? To increase the price ? Hype ? ** Like any audio myth - it has a long and *very sordid* history !!!! Fact: The earliest tube guitar amps all used " tube " rectifiers. Fact: Lectic gittar players are obsessed with the " sound " of early amplifiers - since they falsely associate that with the distinctive playing of many, now legendary, early electric blues and rock guitarists. Fact: Tubes are automatically considered way cool. Fact: It is a given that more tubes are better than less tubes. Fact: The use of tube rectifiers is responsible for maybe just a * tad more noticeable * amount of amplitude compression when the amp is heavily overdriven as compared with otherwise similar SS rectifier models. Fact: If you are in the business of FLOGGING tube guitar amps for an income to live on - then clutching at such tenuous straws is perfectly kosher. Fact: If two is better than one - then three is one better again. PLUS : Never forget THE number one, most fundamental tenet of the AMERICAN way of life: " If some's good, then more is better and TOO MUCH is just right !! " ...... Phil |
#17
Posted to rec.audio.tubes
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Let's talk about tube amps
Eeyore wrote:
No the were not. heat doesn't make rust, moisture and air do. I suspect quite a few of these answers. Being left in a warm damp place ( e.g. Florida ) would encourage rust too. Corrosion is in general a consequence of the operation of a cell. Whatever is required for a cell to operate is needed for corrosion to happen. I would expect an optimum temperature for any particular circumstance. It's likely that at very low temperatures nothing much will happen at all, and if it's too hot something else will happen instead. Steel, in particular, is a very complicated thing. Do rig operators need to replace sacrificial anodes more often in warm seas because of the higher temperature, or less often because of the reduced oxygen content of the water? Boiler flues, for example, can disappear in next to no time, even if they're made of "stainless" steel. There are any number of apochryphal tales of engines destroyed in short order because the cylinder head has been used as an earthing point...particularly old vehicles with bolted-up chasses. Ian |
#18
Posted to rec.audio.tubes
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Let's talk about tube amps
Ian Iveson wrote: Eeyore wrote: No the were not. heat doesn't make rust, moisture and air do. I suspect quite a few of these answers. Being left in a warm damp place ( e.g. Florida ) would encourage rust too. Corrosion is in general a consequence of the operation of a cell. Whatever is required for a cell to operate is needed for corrosion to happen. I would expect an optimum temperature for any particular circumstance. It's likely that at very low temperatures nothing much will happen at all, and if it's too hot something else will happen instead. Steel, in particular, is a very complicated thing. Do rig operators need to replace sacrificial anodes more often in warm seas because of the higher temperature, or less often because of the reduced oxygen content of the water? Boiler flues, for example, can disappear in next to no time, even if they're made of "stainless" steel. There are any number of apochryphal tales of engines destroyed in short order because the cylinder head has been used as an earthing point...particularly old vehicles with bolted-up chasses. One thing for sure. I doubt those transformers were vacuum varnish impregnated. Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address |
#19
Posted to rec.audio.tubes
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Let's talk about tube amps
"Eeyore knows Nothing" One thing for sure. I doubt those transformers were vacuum varnish impregnated. Graham ** Who gives *flying ***** what some manic, ASD ****ed, know nothing pommy idiot like Graham Stevenson "doubts" ?? Based entirely on his MONSTROUS IGNORANCE !!! FYI: The AC supply and valve OP trannys in Mesa Boogie amps ARE nearly all, totally resin impregnated types. Prevents the re-winding of damaged ones. Real PITA. ...... Phil |
#20
Posted to rec.audio.tubes
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Let's talk about tube amps
Fact: The earliest tube guitar amps all used " tube " rectifiers. Fact: Lectic gittar players are obsessed with the " sound " of early amplifiers - since they falsely associate that with the distinctive playing of many, now legendary, early electric blues and rock guitarists. It isn't false, it's a big component. However, so were the strings used in those days, which were like telephone wires as compared to modern ones. Fact: Tubes are automatically considered way cool. Fact: It is a given that more tubes are better than less tubes. If you use enough rectifier tubes there is no sag, defeating the purpose. Fact: The use of tube rectifiers is responsible for maybe just a * tad more noticeable * amount of amplitude compression when the amp is heavily overdriven as compared with otherwise similar SS rectifier models. Tube rectifier sag makes a BIG difference in dynamic response in most of the vintage amps when highly overdriven. |
#21
Posted to rec.audio.tubes
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Let's talk about tube amps
The AC supply and valve OP trannys in Mesa Boogie amps ARE nearly all, totally resin impregnated types. Prevents the re-winding of damaged ones. There are effective resin strippers that will leave you with clean lams and bare copper wire. You can reuse the endbells and lams, I guess. |
#22
Posted to rec.audio.tubes
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Let's talk about tube amps
"Bret LIAR" Tube rectifier sag makes a BIG difference in dynamic response in most of the vintage amps when highly overdriven. ** Laughably stupid ********. ...... Phil |
#23
Posted to rec.audio.tubes
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Let's talk about tube amps
Eric wrote:
The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, In what way does "up and up" differ from "up"? What do you mean by shorted? I can understand that you want to join in with all the fun we have here, so I don't wish to dampen your ardour, but you need to think and write more clearly. Try proper paragraphs. It might be useful, for the purpose of grasping how transformers work, to consider what happens if just some of the primary windings become shorted. Would that lead to an increase in secondary voltage? There is an obvious theoretical reason to think that it might, and a rather more complicated reason, to realise that it most probably won't. The best assumption is that the manufacturer has used as few turns as possible. Your shorted primary hypothesis is not best tested by plugging it into the mains. But it made me think of a nice example of a "reductio ad absurdam". If you continue to short primary turns, then secondary voltage should keep rising because the turns ratio increases. In that case, when you have no turns, then you should have a very high secondary voltage indeed. it still does this but no output tubes were in place as I tested it. Still does what, exactly? HT voltage will normally be higher with valves removed, but by how much depends on the details of the circuit, which few here will be familiar with. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. Likely to be normal. The difference is because the two halves will have the same number of turns, but can't occupy the same space, so one will have a different average coil diameter, and so a different length of wire. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? Any thoughts? Explosions are scarce, I should imagine, although you could have fun thinking up a possible scenario. I wonder how much of the contents would have to vaporise before sufficient positive pressure resulted? Implosions are more likely, because of the vacuum. Ian I meant that when first powered up the voltage was normal for a low load condition and over a period of a few minutes the voltage increased about 12 percent. The transformer also buzzed more as it warmed and this was the case with a Marshal I repaired a few years ago that needed a power transformer. I checked the line voltage and it was constant at 117 volts. My area has an old power system. So I was thinking only a few windings had shorted before I discontinued the test. The leaking potting material also lead me to think the transformer was likely to be defective. "The drinking man's favourite model." Yes this is the most probable explanation for the glass fragments. Perhaps a collision between power tubes and beer bottle lead to the amps present condition. Is it not likely that a test not using line voltage would not heat the transformer and therefor not show a short? I did fail to provide enough information in my first post but would be pleased to let the blame fall on the US educational system for the sentence structure. Shorted primary isn't the same thing in most ppls heads as shorted primary turns. At bottom-left he http://www.ivesonaudio.pwp.blueyonde...lustration.GIF is the usual and *very* useful low-frequency model of a transformer. At high frequencies it becomes necessary to include winding capacitance and leakage inductance, but for your purpose the simple example shown is OK. From left to right, there's the primary winding resistance in series with the primary inductance. In parallel with the primary inductance is the load, made up of the secondary winding resistance in series with the resistance presented by your amp, both of which should be multiplied by the square of the turns ratio, Tprimary/Tsecondary. Notice that the primary winding resistance carries the current attributable to the load, *and* that which flows through the primary inductance. If you short turns on the primary, you reduce the turns ratio *and* the primary inductance. Both changes result in extra primary current. Considering also that the inductance falls by the square of the proportion of turns lost, the increase in current is much greater than the reduction in primary winding resistance, so the power it dissipates rises steeply, so it gets hotter. If it was already hot enough to cause a fault, then hotter still is likely to lead to catastrophic failure. If you must test using the mains, then you should at least work out beforehand what you need to measure during the test, and what you expect the measurements to be if your theory is correct. You should also eliminate as much extraneous circuitry as possible...easily done in your case by disconnecting the transformer from the amp and using a suitable resistor instead. Then you can do your test quickly and effectively and just once, thus minimising the risk of causing further damage. If you measure the AC primary and secondary voltages with no load, and divide the one by the other, you get the turns ratio, hopefully in the no-fault condition. If you measure primary current and secondary voltage under load, then wait for the fault to occur and measure them again, you will have all the data you need. A little algebra will then tell you whether your theory fits the facts. Remember that inductance is proportional to the square of the number of turns. Once you've calculated the change in turns ratio, you can infer the proportional reduction in primary inductance. Then you can work out the expected increase in current due to load and inductance, and compare that to your measurement. If you are right you will be seeing something that Phil has never seen before, so it's probably very rare and an experience to be savoured. Certainly it's not a condition that's likely to last for very long. Theory is likely to be of academic interest only, as it sounds like you need a replacement transformer anyway. Ian |
#24
Posted to rec.audio.tubes
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Let's talk about tube amps
PS...
There's a complication that's worth putting as a question because it's a bit interesting to think about. As primary turns are reduced, will there come a point at which the core saturates? If it does approach saturation in your case, then inductance is reduced still further. I've assumed that, if you do get a higher secondary voltage when the fault occurs, then the core permeability is roughly constant. That may not be a safe assumption. If permeability varies significantly, then inductance will no longer be proportional to the square of the number of turns, the experiment becomes invalid, and impossible anyway because you are using a reasonably rated fuse, of course, which will blow quicker than you can measure. Ian |
#25
Posted to rec.audio.tubes
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Let's talk about tube amps
Phil Allison wrote: "sortech" I posted a while back about rusty transformers and got lots of response. It turns out they were rusty because the amp had been ridiculously over heated. ** Utter nonsense. The amp has been allowed to get wet - most likely from condensation while in storage. I see that all the time. The amp is a mesa boogie tipple rectifier and some fool had added a resistor to the bias supply increasing the cathode current. He must have had some interesting sounds as the power transformer primary shorted and B+ went up and up, ** No such thing happens. Shorted turns in the primary causes large currents to flow and makes the AC fuse blow. lots of nasty stuff under the power trans that is some kind of potting compound. So it needs that replaced but I am not sure if the output trans is good or not. The primary reads 21 and 23 ohms from the center tap. ** Sounds about right. This is a 160 watt amp with 6-6l6GC's. The output trans is good and rusty so I am sure it got overheated as well. ** Drivel. Also there was lots of glass chips from the output tubes under the chassis, could the tubes have exploded? ** If output tubes get wet during use, the glass often breaks. They break if you hit them hard enough. They break if they bang into each other .... ..... Phil I have to agree with your assessment. The OP does have some further learning to achieve before he understands why **** happens in guitar amps; maybe with time and experience, he may learn, but usually it takes an average mind about a year or two working as a tech in a repair shop to to fully understand guitar amps after fixing maybe 50 of them, and seeing all manner of **** that's happened. Patrick Turner. |
#26
Posted to rec.audio.tubes
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Let's talk about tube amps
Phil Allison wrote: "Eeyore knows Nothing" One thing for sure. I doubt those transformers were vacuum varnish impregnated. Graham ** Who gives *flying ***** what some manic, ASD ****ed, know nothing pommy idiot like Graham Stevenson "doubts" ?? Based entirely on his MONSTROUS IGNORANCE !!! FYI: The AC supply and valve OP trannys in Mesa Boogie amps ARE nearly all, totally resin impregnated types. Prevents the re-winding of damaged ones. Real PITA. ..... Phil Yes, but good varnishing does make a given tranny less likely to fail early. Now I have had to repair many amps and have never ever bothered to try to unwind a traumatised tranny then remove E&I lams which have been glued together with varnish and re-wind it after trying desperately trying to save the bobbin . The cost in time is absurd, and its always cheaper to buy a spare and install it. They are widely available. However, sometimes one might want to recover the core material so it can be re-used, and then one has to place the pharqued tranny in a small wood fire until it just glows dull read for a few minutes and this vapourizes and burns off all the plastics and varnish. I've done barrow loads of stuffed PT, OPT, and chokes in my open fireplace in my loungeroom, so I have a stock of various sized cores which I use mainly for new chokes. The core material is left to cool slowly and next day the wire can be cut off with side cutters or angle grinder and bolts removed and the laminations will easily all fall apart. The magnetic properties should not be changed. Re-winding can be done, but with a new bobbin and wire, but usually I always try to re-wind with a taller stack of iron with more turns per volt and less losses to make a better transformer than original. Where you have an E&I core which has been machine welded together, and which has no bolt holes, then it is always a throwaway item. The commonly used GOSS lams are often now machine welded after just butting a pile of E and I without interleaving the E and I. The permability obtained is high enough. Patrick Turner. |
#27
Posted to rec.audio.tubes
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Let's talk about tube amps
Phil Allison wrote: "sortech" I meant that when first powered up the voltage was normal for a low load condition and over a period of a few minutes the voltage increased about 12 percent. ** Bizzare. Been servicing valve guitar amps for 4 decades and never seen that. Even a few shorted turns blows the AC fuse, real quick. It depends where the shorted turns are. If you had a couple of shorted turns in a low voltage heater winding, the tranny would not blow a mains fuse immediately, but after 1/2 an hour it would be scorching hot and maybe hum a bit, and maybe the fuse blows when other shorted turns develop as turns near the initial sorted turn get roasted by the high local heat. The transformer also buzzed more as it warmed ** Very common for loose laminations to begin to buzz when the tranny warms up. And when the plate current begins to be drawn, and the peak charge currents in the rectifiers become substantial. I checked the line voltage and it was constant at 117 volts. My area has an old power system. So I was thinking only a few windings had shorted before I discontinued the test. The leaking potting material also lead me to think the transformer was likely to be defective. ** That last bit indicates a bad tranny. Plus an evil smell and popping /cracking noises as it heats up. If the tranny is estimated to be a 150VA tranny, the input current from the mains with no loads connected on the secondary should be less than 15% of the full load current. But with all tubes out of the sockets and no load, including rectifier tubes. With no load, and Si diodes left connected, B+ should not exceed the capacitor voltage ratings. Novices won't know what dangers lurk by leaving all the tubes out and they don't know what to check and look for whiloe testing things. The transformer temperature should not rise more than 15C above room temp with no load after 1 hour; if it gets really hot its a bad tranny. "The drinking man's favourite model." Yes this is the most probable explanation for the glass fragments. Perhaps a collision between power tubes and beer bottle lead to the amps present condition. ** The " Triple Rectifier" is famously known as the model played by Saddam Hussein. Even his friends said he sounded like Sheite .... Well, I really doubt they would have ever said that, because they would have known the consequences were not a happy story..... If they didn't like his tunes, he would give them his old worn out 6L6, and tell them to eat them for breakfast at gunpoint. Even on a sunni day. Patrick Turner. ..... Phil |
#28
Posted to rec.audio.tubes
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Let's talk about tube amps
Bret L wrote: Fact: The earliest tube guitar amps all used " tube " rectifiers. Fact: Lectic gittar players are obsessed with the " sound " of early amplifiers - since they falsely associate that with the distinctive playing of many, now legendary, early electric blues and rock guitarists. It isn't false, it's a big component. However, so were the strings used in those days, which were like telephone wires as compared to modern ones. Fact: Tubes are automatically considered way cool. Fact: It is a given that more tubes are better than less tubes. If you use enough rectifier tubes there is no sag, defeating the purpose. Fact: The use of tube rectifiers is responsible for maybe just a * tad more noticeable * amount of amplitude compression when the amp is heavily overdriven as compared with otherwise similar SS rectifier models. Tube rectifier sag makes a BIG difference in dynamic response in most of the vintage amps when highly overdriven. Nope, the B+ sags more than 20% under high load, and the dynamics tend to become compressed. And because so many guitar amps have **** all B+ filtering, and work in near class B and even in class C during highest over drive power, then the hum voltage at the OPT CT becomes high making the square waves produced contain a "gravelly" tone, much loved by those who are confused about what constitutes real music. I have noticed that Marshall and Fender have often supplied amps to export markets say in Oz **without** filter chokes and a second B+ cap which is seen on the schematics for the amps concerned when you read the Groove Tube circuit book. The exporters save in 3 ways. Less expense to make the amp, less expense of freight, and less chance of unhappy rock stars in distant nations turning up at the factory wanting to shove the guitar amp up the CEOs arsole because it failed to meet their expectations. Many guitar amps **do** have good B+ filtering just like most hi-fi amps. But they all work in class C to make a bunch of square waves when the input goes 20% above that needed for sine wave clipping. When I weigh up what musicians say about the tone of their guitar amps and about their idea of technicals I can only smile. And if you want the sound George Benson or Mark Knoffler gets as their signature sound, be prepared to think slightly differently. Patrick Turner. |
#29
Posted to rec.audio.tubes
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Let's talk about tube amps
On Aug 30, 4:20*am, Patrick Turner wrote:
Nope, the B+ sags more than 20% under high load, and the dynamics tend to become compressed. Now see...thats what makes this particular amp a retarded design. 3 pairs of 6L6s....when are you going to be able to open it up enough to hear a difference from voltage sag? Unless yer playing a 12,000 seat arena and refuse to use the house PA, its kinda useless. Marketing hooey. A 15-35w amp? Sure then you'd be able to wind it up to get the desired compression. It'll still be damn loud. I have that same model "rectumfrier" on the bench right now. Came in with 2 filament failures....one recto tube and the first preamp tube. He's getting the 2 good 5U4s back in a cardboard box. The guy never uses the tube recto'd supply anyway so there's no need to even have them in the sockets pulling filament current. |
#30
Posted to rec.audio.tubes
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Let's talk about tube amps
Hi,
The tube rectifier can make a pretty big difference in the dynamics of a guitar amp. But, another important factor is the actual design and how the thing is biased. I build a guitar amp using a pair of cathode biased EL34's where, at idle, the thing pulls darn near the same plate current through the EL34's as it does at the point where it starts to clip. I use a 5U4 rectifier and the same power transformer as found in Dynaco's ST70 power amp to power this 32 watt push pull guitar amp. My power supply, at clipping sags about 20 volts. My Fender Bandmaster (1965 version) sags more if you compare the B+ during a light load and then during light clipping. The Bandmaster has solid state rectifiers in it's B+ power supply. Also, depending on which of the three negative feedback settings you have the feedback switch set to on my amp, the dynamics, and especially the tightness of the bass, change a lot. If the phase splitter isn't adjusted correctly for AC balance, the amp can sound rather odd as well and lack punch and power. Your comment about strings is right on! Wow, someone else realizes this. Thick strings were very much the norm back in the day. Also, the pickups used back then were a lot different sounding. There are a lot of variables when designing a guitar amp. The electronics is only one part of the puzzle. Patrick Turner wrote: Bret L wrote: Fact: The earliest tube guitar amps all used " tube " rectifiers. Fact: Lectic gittar players are obsessed with the " sound " of early amplifiers - since they falsely associate that with the distinctive playing of many, now legendary, early electric blues and rock guitarists. It isn't false, it's a big component. However, so were the strings used in those days, which were like telephone wires as compared to modern ones. Fact: Tubes are automatically considered way cool. Fact: It is a given that more tubes are better than less tubes. If you use enough rectifier tubes there is no sag, defeating the purpose. Fact: The use of tube rectifiers is responsible for maybe just a * tad more noticeable * amount of amplitude compression when the amp is heavily overdriven as compared with otherwise similar SS rectifier models. Tube rectifier sag makes a BIG difference in dynamic response in most of the vintage amps when highly overdriven. |
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