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#1
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Is there an easy way to know when a tube has "warmed up"?
I am hoping that someone in this group can help me out on this one. I have
been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#2
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John Andreen wrote:
What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Rig a circuit that measures the current from the cathodes of the tubes. Almost by definition, a tube is warmed up when it is drawing at least 90% of the current it will normally draw. If measuring cathode current is awkward, measure the current going to the plates and screens. Measuring the current is the best thing to do, as this tells you exactly what you need to know. Measuring the temperature of the glass bulb of a tube doesn't really tell you when a tube is ready to go to work. And if the power should go off for a short while, the glass won't cool off for a long while. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. How about using output transformers? You can use a transformer normally rated for say 2000 ohms impedance to 4 ohms impedance for 2 ohm loads. However the input impedance will change from 2K to 1K, but the power handling will be 3dB less. More bass though. So use bigger transformers. With audio transformers, when operating at impedances below those specified, power capability is lower and the frequency spectrum is shifted downward, conversely, at higher impedances power capability and frequency spectrum will be shifted upward. Then you can go all tube without the BJTs. And the transformers give excellent DC isolation to the speakers. Be sure to enclose the tubes so moving objects don't damage them or get damaged by the tubes. And firmly bolt the amp down (but check before drilling holes in the trunk that you don't puncture into the gas tank!). |
#3
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just set timer for 15 sec.
dc sensing protection circ on output will do the rest of job. -- .................................................. ........................ Choky Prodanovic Aleksandar YU "don't use force, "don't use force, use a larger hammer" use a larger tube - Choky and IST" - ZM .................................................. ........................... ... "John Andreen" wrote in message news:_Mmkb.70789$vj2.17282@fed1read06... I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#4
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Simple answer: the God of Triodes is paying you back for putting silicon
in the signal path. :-} Tim -- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms "John Andreen" wrote in message news:_Mmkb.70789$vj2.17282@fed1read06... I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#5
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Thank you for the very informative response. I think that I will indeed
measure the current flowing into the Vacuum tubes. Not real hard to do really. I had considered that back in 1998, but gave it up due to complexity. Your input made me take another look. Already found a cool hall effect sensor ( considered using MAXIM's IC before) that will really do a nice job. Kudo's, Kudo's, Kudo's. I am indeed greatful for this input as I was certain that bottle temperature would be a terrible lag lead location. Thought that by measuring the pin temperature would be somewhat better. Your idea is much better. Thanks. I do know that most Valve amplifiers use the Audio transformers. Did a short study a long time ago using my companys 2 KRELL KA300's ( I think), and a high end tube amplifier that we had for evaluation at Apogee in our sound lab. I do not recall the amplifier brand. I don't even know if it was branded come to think of it. Came from Europe though, probably Germany. Anyways I ran the Valve amplifier with a Pass Labs preamplifier and a KRELL CD player. Played this through a pair of Totem acoustics speakers. OMG, the music was wonderful! The listening material was comprised of Mahalia Jackson, Claire Marlo ( Let It Go), Yello (Baby) and Thursday Diva (Follow Me). Next I ran a set of Apogee Diva's on the Valve amplifier setup. Could only play at relatively low volume and it didn't sound good. Tried again with a much less demanding pair of Apogee Ribbon/Hybrid's. I think they were Perseus's. Once again the music sounded stunning! I then did the same listening test with the KRELL's as the amplifier stage. Outstanding musicallity with the Diva's and the other two speaker pairs. I came to the conclusion that the Diva's really need a low impedance source to drive them properly. They also liked POWER. The Diva's when properly operated were simply the best speakers that I have ever heard. Maybe I'm biased. My mind isn't completely made up about audio transformers. But the **really** good ones are ballistically expensive and take up an awful lot of room. Too bad nobody has been able to make a better, more efficient transformer. I guess you could throw make it the size of a cigarette pack too. That is why I keep looking back at hybrid designs. Hell, I even know some of the Engineers that are still working on ways to make a silicon based amp sound just like a tube. 10+ years and still not even close. John "Robert Casey" wrote in message ... John Andreen wrote: What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Rig a circuit that measures the current from the cathodes of the tubes. Almost by definition, a tube is warmed up when it is drawing at least 90% of the current it will normally draw. If measuring cathode current is awkward, measure the current going to the plates and screens. Measuring the current is the best thing to do, as this tells you exactly what you need to know. Measuring the temperature of the glass bulb of a tube doesn't really tell you when a tube is ready to go to work. And if the power should go off for a short while, the glass won't cool off for a long while. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. How about using output transformers? You can use a transformer normally rated for say 2000 ohms impedance to 4 ohms impedance for 2 ohm loads. However the input impedance will change from 2K to 1K, but the power handling will be 3dB less. More bass though. So use bigger transformers. With audio transformers, when operating at impedances below those specified, power capability is lower and the frequency spectrum is shifted downward, conversely, at higher impedances power capability and frequency spectrum will be shifted upward. Then you can go all tube without the BJTs. And the transformers give excellent DC isolation to the speakers. Be sure to enclose the tubes so moving objects don't damage them or get damaged by the tubes. And firmly bolt the amp down (but check before drilling holes in the trunk that you don't puncture into the gas tank!). |
#6
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Thank you very much for your input. I do have a DC sense circuit for the
outputs ( shamelessly stolen from somewhere). I also have a small servo that can correct for up to about +/- .5 DC. John "Choky" wrote in message ... just set timer for 15 sec. dc sensing protection circ on output will do the rest of job. -- .................................................. ....................... Choky Prodanovic Aleksandar YU "don't use force, "don't use force, use a larger hammer" use a larger tube - Choky and IST" - ZM .................................................. ........................... .. "John Andreen" wrote in message news:_Mmkb.70789$vj2.17282@fed1read06... I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#7
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I know, I know, but I come from the car audio amplifier world where silicon
is king. Its kind of really all I know. I will say, that I have been studying Valve amplifiers for a few years. Still not able to actually make good comparative reference between BJT's and Vacuum tubes. I matriculated collegiately during the mid 70's and silicon was all that was taught. I am learning though. I even purchased TubeCAD to help me out. It didn't help any when I brought up the subject to my peers in card audio. They slammed Vacuum tube amplifiers, saying horrible things, the nicest being that they called Vacuum tubes "Watt sucking glow FET's". Being willing to compromise, I am shunned by both sides. Most of my silicon based car audio amplifier designs are as simple as possible. If it doesn't need to be in the signal path, then I don't put it there. No crossovers, no bass boost, no treble boost. Hell, not even gain pots. That stuff belongs elsewhere, like in a preamplifier. My design never fly with my boss's as they say they won't sell. They are mostly right, as it is all a matter of perception. More is always better, right? I will say this though, you guys are most certainly the nicer of the two camps. Thanks for the prudent observation! John "Tim Williams" wrote in message ... Simple answer: the God of Triodes is paying you back for putting silicon in the signal path. :-} Tim -- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms "John Andreen" wrote in message news:_Mmkb.70789$vj2.17282@fed1read06... I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#8
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Somewhere in dark past ( ) I build DC300B (I think from AA) hybrid amp
with one my friend; line up is something like triode strapped EF86 on input,then 2 x ECC82 in White Follower ,then 2 pairs of Mosfets on output. trust me-even if White Follower wasn't direct coupled with mosfets,thumpboingoink cycle was evident. installing 15 sec delay for powering xformer for output stage cured everything. if you have mutual xformer for tube and SS supply,you can implement sort of mute circ in tube output part. I mention DC sense circ only as speaker protection precaution,which is must have for every amp DC coupled to speakers. "John Andreen" wrote in message news:3SDkb.71248$vj2.17708@fed1read06... Thank you very much for your input. I do have a DC sense circuit for the outputs ( shamelessly stolen from somewhere). I also have a small servo that can correct for up to about +/- .5 DC. John "Choky" wrote in message ... just set timer for 15 sec. dc sensing protection circ on output will do the rest of job. -- .................................................. ........................ Choky Prodanovic Aleksandar YU "don't use force, "don't use force, use a larger hammer" use a larger tube - Choky and IST" - ZM .................................................. ........................... .. "John Andreen" wrote in message news:_Mmkb.70789$vj2.17282@fed1read06... I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. Thoughts, commentary and ideas anyone? Regards, John Andreen |
#9
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John Andreen wrote: I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. 75 watts of class A means that you would have to have approximately 160 watts of idle dissipation in the transistor outputs. Even for the most rugged devices 80 watts of heat from each is a heck of a lot to expect continuously. How many devices have you got? If it were my amp, I'd have at least 6 devices, perhaps 3 npn, and 3 pnp, in a complementary pair set up. This way the dissipation can be held to less than 30 watts per device, with far greater reliablity. is it common emitter, or common collector? Remember, for SS, for each extra 10C temp rise, there is a 10% fall in reliability. a 100C temp rise = 100% fall in reliability, ie, it WILL fail. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. We really need to see a schematic! The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. You say there are 6L6 tubes used to drive the bjts, and these are directly coupled. Most full SS amps have ALL direct coupling, with an enormous amount of total feedback, perhaps 30 dB in the output stage, in the form of common collector array, ie, emitter follower complementary pair, and then they have perhaps 50 dB of global FB to a differential pair of bjt at the input. This automatically reduces the DC offset at the output to less than a few mV, regardless of the operating temp of ANY devices used which are included in the amp loop. RC coupled preamp stages should not affect the DC offset, unles they are included in the fedback loop, which then couldn't be all direct coupled. ALL direct coupled SS amps have the greatest FB at DC, so thats where the greatest control of output voltage occurs. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. I think your problem has little to do with tube temperature. But we cannot be certain, because you have not posted a schematic which we can properly analyse. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. Timed relays are used on much SS gear, but also the relay turn on circuit is controlled by fault detection circuits, and it isn't until the DC offset is low at the output that the relay will trip on, to connect speakers, when its safe to do so. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. This sounds like a nightmare to R&D! Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. It depends how you are running the tube. We need a schematic! BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. For car audio, and for those who like brain mashing levels of sound, fitting a pair of amps like those shown at http://www.turneraudio.com.au/htmlwe...00monobloc.htm would be difficult to implement, but two of the amps shown will provide 600 watts of power. The problem is, where do you place 100 kGs of hot hardware, and you would need a 1 kW inverter. Maybe someone with a huge mobile trailer home might use them.... There is no problem driving low loads, and the above amps are able to be matched to 2 ohms, without losses. Most tube amps with OPTs don't have sufficient multiple secondary sectionjs to allow them to be coupled to less than 4 ohms. But I assure you that with sufficient secondary sections, and by using ALL of them AND with equal current density in all of them, then a match to 1 ohm is quite possible. Thoughts, commentary and ideas anyone? BTW, I have built a pair of class A mosfet output stages coupled to the speakers with an OPT, and driven by 3 x small signal transitors. See http://www.turneraudio.com.au/webpic...no400w288h.jpg See http://www.turneraudio.com.au/htmlwe...5050mosfet.htm The driver transitors are RC coupled to the output stage, which has 4 x 2SK134, arranged like a quad of tubes, and RC coupled to the transformer. Fixed bias is used for the class A mosfets, since they have a negative temp coefficient, which means they conduct less current as they get hotter, so fixed bias is safe. There is no need for output relays, since there is NO direct couping, and the output fets cannot let DC pass the the speakers from the rails in a fault condition. The amp's full power response is 10 Hz to 65 kHz, sufficient for all of what I listen to. I am planning to upgrade these class A mosfet amps by use of 2SK369 j-fet devices in the input/driver stage, and hopefully that will silence the critics who are prejudiced about transistors. Some are prejudiced against mosfets, and even j-fets, and I hope they recover from their ailment soon. Long Live Output Transformers!!! ( Those who say it can't be done, just cannot do it; so, may they learn.) Finally, I use EL84 strapped as triodes for driver tubes, since one is equal to 5 halves of a 6SN7. Now in a class A tube power amp, the EL84 in an output stage is run at 12 watts dissipation, with say B+ = 300v, and Ia = 40 mA. But in driver situation, I typically run the EL84 at Ea = 240v, and Ia = 15 mA, and the temperature is a lot less. Both either application, the working temp is correct. Minor differences in ambient temp will affect the tube temp, but not enough to dramatically upset the working of the circuit where it works. BJTs on the other hand are HORRIBLY temperature sensitive, and troubles with class A amps "running away thermally" is not uncommon, becaue the hotter they get, the more current they conduct, ie, they have a horrible positive thermal coeficient. I have never had any reason to ever use a BJT in an outout stage yet on any amp. Also, BJTs need to have a high current applied to their bases to drive them, which may be why you have to use a 6L6 to do that. Darlingtom pair connection will reduce this drive current. But I just use mosfets, because their gate drive is high impedance, like a tube. The down side is that mosfets have high input capacitance, but using appropriate low impedance drive circuitry to achieve a high time constant for the RC involved solves that problem. Patrick Turner. Regards, John Andreen |
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Most tube amps with OPTs don't have sufficient multiple secondary sectionjs to allow them to be coupled to less than 4 ohms. But I assure you that with sufficient secondary sections, and by using ALL of them AND with equal current density in all of them, then a match to 1 ohm is quite possible. If I understand the high power car audio area correctly, they use many speakers wired in parallel. To get a very low impedance so you can get a lot of power from 12V DC. If you rewire the speakers to present a higher load impedance, you should be able to drive them with a convential tube amp circuit with convential output transformers. A series/parallel arrangement of the speakers. (I can understand that this may not be an option in the market, though. Not "swap it out/in and play") As far as the amp's power supply, run all the heaters off of the 12VDC (the value 6.3V for heaters came from tube manufacturers wanting to make tubes for car radios). The 6.3V output tube heaers can be wired in series for use on 12V. But you need to have a DC-DC converter from 12V to the B+ you need at the current you need. A switchmode supply operating around 100KHz (frequency to avoid noise in the audio, also no beat frequencies from audio and 100KHz invading the audio spectrum). |
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Patrick,
Thanks again for all the wonderful insight. I would love to provide a schematic, but I do not know the legalities involved. It is in fact intellectual property of a rather large audio company. They have deep pockets and mean lawyers. Trust me on this, I know whom they have litigated and sent into the depths of oblivion. I was only given a copy of the schematic out of friendship and on the condition that I won't reveal it. It could also compromise my friend and his position. As a side note, this companies Non-Disclosure agreement is 28 pages of legalistic mumbo jumbo and folderol. I can however, publish a schematic of my modified design when I am completed or near completion. I must be able to show that this is my own design, complete with a minimum of 7 unique differences. This is really why I am asking some of the questions that I ask. Slowly but surely identifying the *major* design flaws and then creating my own circuits to hopefully correct them. I may know much about silicon audio, but I am for sure a pleeb at vacuum tubes. When I get home, I will check the schematic and count the output devices. Just from memory, I am certain that there are at least 6 sets of complementary pairs. Car audio is really a harsh environment to design for( this is not the case for my design, as I want to drive my Apogee's at home). Most output devices are operated at a maximum heatsink temperature of about 90 degrees C. So taking into account device derating, it is rather common to use an excess of output devices. And, in a car, it could be in Gnome, Alaska one day and in Death Valley the next. Currently, I am still working on the PS sections. This includes the tube heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the rails for the output BJT's, and the +/- 15 volt rails for the support circuitry. Haven't made it to the audio sections yet. Hell, I am still having a tough time understanding that there is only 1 kind of tube and not P and N tubes like transistors. This might seem like another odd question, but has anyone ever made an audio amplifier using anything like the really big transmitting tubes. I used to work on multi-kW RF generators in the '70s. They used to scare me to death when I worked on them due to having to use a grounding bar to discharge the large glass capacitors. Kept thinking that I would one day forget to do this and vaporize myself. I little more info is probably needed to clarify some of my posts. The original design was ment to be used in a car audio environment. It was never produced. The gentleman that designed the amplifier now works for a well known home audio company. The company that holds the intellectual property on the original design is a large card audio company. Although my considerate friend no longer works for the car audio company, were he to be sued for IP theft, it would not look good to his current employer. I want to use this amplifier design as a base for a home style amplifier to power my Apogee Ribbon speakers. Check this site for Apogee info: http://www.apogeespeakers.totalserve.co.uk Although it is a hybrid, I do like the sound of the original amplifier. This is pretty much a labor of love, or I probably would have given up and simply made a Leach amplifier with more outputs. Check this site for Leach amplifier info: http://users.ece.gatech.edu/~mleach/lowtim It too is a nice sounding amplifier. Please don't hate me for this, but if you look into the Apogee Speakers, you will see just how difficult they are to drive even with really big KRELL amplifiers. This is why I am willing to compromise and do a design that uses both worlds. I have done many spectral analysis tests on both valve and SS amplifiers. I can see the differences. I can even hear the difference. Valve amplifier sound makes me feel more relaxed and comfortable. With many SS amplifiers, I feel as if I should be clenching my fists in anger. Perhaps a hybrid amplifier will make me feel more comfortable while clenching my fists. John Andreen BTW: I live in AZ, and many of my "tubehead" friends use supplemental air conditioning units in their audio rooms. Is this normal? Patrick Turner" wrote in message ... John Andreen wrote: I am hoping that someone in this group can help me out on this one. I have been working on an amplifier design for some time now. It is a Hybrid amplifier that can produce 75W x 2 into 2 Ohms. Yeah I know......, but hear me out. 75 watts of class A means that you would have to have approximately 160 watts of idle dissipation in the transistor outputs. Even for the most rugged devices 80 watts of heat from each is a heck of a lot to expect continuously. How many devices have you got? If it were my amp, I'd have at least 6 devices, perhaps 3 npn, and 3 pnp, in a complementary pair set up. This way the dissipation can be held to less than 30 watts per device, with far greater reliablity. is it common emitter, or common collector? Remember, for SS, for each extra 10C temp rise, there is a 10% fall in reliability. a 100C temp rise = 100% fall in reliability, ie, it WILL fail. I am using all vacuum tubes, mostly Svetlana 6LCGC's in the preamplifier and predriver stages and a class-A output stage using BJT's. The output BJT's that I am using are 2SA1303 and 2SC3284, but will probably change to On Semiconductor MJW21193 and MJW21194's. The BJT output stage is directly coupled to the Vacuum tube predriver stage and the preamplifier to predriver stages are capacitively coupled. We really need to see a schematic! The design is not my own, but I got the schematics from a good friend who works as an Electrical Engineer for a very high end home audio company. I have heard this design actually play. It really did sound quite good. I digress. Here is my problem. If I attempt to play any audio prior to the vacuum tubes being fully warmed up, it has a tendency to rail negative at the outputs. Transistors are rather expensive when you go thru them like popcorn. Actually, I have been able to add protection circuitry to keep the output devices from blowing up. But, I believe that I could probably take out a tweeter or two if I'm not real careful. I have Apogee Speakers with their wonderful ribbons, and I really don't want to damage something that can not easily be replaced. You say there are 6L6 tubes used to drive the bjts, and these are directly coupled. Most full SS amps have ALL direct coupling, with an enormous amount of total feedback, perhaps 30 dB in the output stage, in the form of common collector array, ie, emitter follower complementary pair, and then they have perhaps 50 dB of global FB to a differential pair of bjt at the input. This automatically reduces the DC offset at the output to less than a few mV, regardless of the operating temp of ANY devices used which are included in the amp loop. RC coupled preamp stages should not affect the DC offset, unles they are included in the fedback loop, which then couldn't be all direct coupled. ALL direct coupled SS amps have the greatest FB at DC, so thats where the greatest control of output voltage occurs. What I am thinking of doing is to add a couple of relays at the speaker outputs, and then driving them on only when the vacuum tubes have properly warmed up. I think your problem has little to do with tube temperature. But we cannot be certain, because you have not posted a schematic which we can properly analyse. What I don't know is just exactly when to drive them on. I could simply use an RC timer circuit that waits x seconds and then drives on the relays. Timed relays are used on much SS gear, but also the relay turn on circuit is controlled by fault detection circuits, and it isn't until the DC offset is low at the output that the relay will trip on, to connect speakers, when its safe to do so. But, if ambient temperature is much colder than normal, then this is not a really great solution. Instead, I was thinking of placing thermistor(s) in close contact with the vacuum tubes and then analog *and* these thermistors via a set of comparator circuits to eventually drive the relays on. That way, the relays would only activate when all the vacuum tubes are up to temperature. This sounds like a nightmare to R&D! Now, what I don't know is at what temperature is a vacuum tube considered "warmed up". I am looking for a general answer for a minimum temperature that would be considered safe. I know that different vacuum tubes probably will operate at vastly different temperatures. It depends how you are running the tube. We need a schematic! BTW I love valve amplifiers and I extoll their virtues to all who will listen. Sadly, few do. My world is that of car audio and if it doesn't have the ability to drive the impedance of a nail with all the power in Thor's mighty hammer, then it doesn't sell. You are thinking then, why the hybrid you #$$#%$#? Simple, I love my Apogee's and they have a rather low impedance that any low cost Valve amplifier can't drive. For car audio, and for those who like brain mashing levels of sound, fitting a pair of amps like those shown at http://www.turneraudio.com.au/htmlwe...00monobloc.htm would be difficult to implement, but two of the amps shown will provide 600 watts of power. The problem is, where do you place 100 kGs of hot hardware, and you would need a 1 kW inverter. Maybe someone with a huge mobile trailer home might use them.... There is no problem driving low loads, and the above amps are able to be matched to 2 ohms, without losses. Most tube amps with OPTs don't have sufficient multiple secondary sectionjs to allow them to be coupled to less than 4 ohms. But I assure you that with sufficient secondary sections, and by using ALL of them AND with equal current density in all of them, then a match to 1 ohm is quite possible. Thoughts, commentary and ideas anyone? BTW, I have built a pair of class A mosfet output stages coupled to the speakers with an OPT, and driven by 3 x small signal transitors. See http://www.turneraudio.com.au/webpic...no400w288h.jpg See http://www.turneraudio.com.au/htmlwe...5050mosfet.htm The driver transitors are RC coupled to the output stage, which has 4 x 2SK134, arranged like a quad of tubes, and RC coupled to the transformer. Fixed bias is used for the class A mosfets, since they have a negative temp coefficient, which means they conduct less current as they get hotter, so fixed bias is safe. There is no need for output relays, since there is NO direct couping, and the output fets cannot let DC pass the the speakers from the rails in a fault condition. The amp's full power response is 10 Hz to 65 kHz, sufficient for all of what I listen to. I am planning to upgrade these class A mosfet amps by use of 2SK369 j-fet devices in the input/driver stage, and hopefully that will silence the critics who are prejudiced about transistors. Some are prejudiced against mosfets, and even j-fets, and I hope they recover from their ailment soon. Long Live Output Transformers!!! ( Those who say it can't be done, just cannot do it; so, may they learn.) Finally, I use EL84 strapped as triodes for driver tubes, since one is equal to 5 halves of a 6SN7. Now in a class A tube power amp, the EL84 in an output stage is run at 12 watts dissipation, with say B+ = 300v, and Ia = 40 mA. But in driver situation, I typically run the EL84 at Ea = 240v, and Ia = 15 mA, and the temperature is a lot less. Both either application, the working temp is correct. Minor differences in ambient temp will affect the tube temp, but not enough to dramatically upset the working of the circuit where it works. BJTs on the other hand are HORRIBLY temperature sensitive, and troubles with class A amps "running away thermally" is not uncommon, becaue the hotter they get, the more current they conduct, ie, they have a horrible positive thermal coeficient. I have never had any reason to ever use a BJT in an outout stage yet on any amp. Also, BJTs need to have a high current applied to their bases to drive them, which may be why you have to use a 6L6 to do that. Darlingtom pair connection will reduce this drive current. But I just use mosfets, because their gate drive is high impedance, like a tube. The down side is that mosfets have high input capacitance, but using appropriate low impedance drive circuitry to achieve a high time constant for the RC involved solves that problem. Patrick Turner. Regards, John Andreen |
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John Andreen wrote:
Patrick, Thanks again for all the wonderful insight. I would love to provide a schematic, but I do not know the legalities involved. It is in fact intellectual property of a rather large audio company. They have deep pockets and mean lawyers. Trust me on this, I know whom they have litigated and sent into the depths of oblivion. I was only given a copy of the schematic out of friendship and on the condition that I won't reveal it. It could also compromise my friend and his position. As a side note, this companies Non-Disclosure agreement is 28 pages of legalistic mumbo jumbo and folderol. I can however, publish a schematic of my modified design when I am completed or near completion. I must be able to show that this is my own design, complete with a minimum of 7 unique differences. This is really why I am asking some of the questions that I ask. Slowly but surely identifying the *major* design flaws and then creating my own circuits to hopefully correct them. I may know much about silicon audio, but I am for sure a plebe at vacuum tubes. When I get home, I will check the schematic and count the output devices. Just from memory, I am certain that there are at least 6 sets of complementary pairs. Car audio is really a harsh environment to design for( this is not the case for my design, as I want to drive my Apogee's at home). Most output devices are operated at a maximum heatsink temperature of about 90 degrees C. So taking into account device derating, it is rather common to use an excess of output devices. And, in a car, it could be in Gnome, Alaska one day and in Death Valley the next. Currently, I am still working on the PS sections. This includes the tube heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the rails for the output BJT's, and the +/- 15 volt rails for the support circuitry. Haven't made it to the audio sections yet. Hell, I am still having a tough time understanding that there is only 1 kind of tube and not P and N tubes like transistors. There's the quasi-complementary style circuit, with two tubes stacked totem pole style. Something like http://headwize2.powerpill.org/proje...=cmoy5_prj.htm figure 1 You could change things so the bottom tube's cathode circuit is fed by a negative power supply, and the top tube's plate circuit fed by a positive power supply. And the top tube's grid tied to ground thru a 500K resistor. You wouldn't use this exact circuit, as you want more power and low impedance. But this topology should suggest possibilities. |
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David R Brooks wrote in
: For *real* B+ power in a car, why not a 3-phase transformer fed direct from the alternator? That solution is a bit expensive as 3 phase outputs are rather rare on automotive alternators. Another factor is that most automotive alternators will cook themselves if constant high current demands are made on them. Now if you add a truck alternator modified with 3 phase outputs, that might resolve the reliability issue, but the voltage will vary quite a bit so regulation is a must. When all is said and done, you might as well put a honda generator in the trunk/boot. It would be cheaper and probably better. r Robert Casey wrote: [snip] :But you need to have a DC-DC converter from 12V to the B+ you need at the :current you need. A switchmode supply operating around 100KHz frequency to avoid noise in the audio, also no beat frequencies from audio and 100KHz :invading the audio spectrum). -- Nothing beats the bandwidth of a station wagon filled with DLT tapes. |
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Simpleton question:
What is JPT????????? jack |
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j wrote: Simpleton question: What is JPT????????? jack Don't know, and can't even find it in the original post. acronymfinder.com gives a few possibilities, like "Joint Project Team", but none that seem to fit into the context of this thread. Cheers, Fre -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ |
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j wrote:
Simpleton question: What is JPT????????? jack You must mean "BJT". That's "Bipolar Junction transistor", AKA NPN and PNP transistors. As opposed to FETs..... |
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I am not sure why it is not yet being done? But, I was discussing something
along the same lines with a gentleman at a computer swap I sell at. It goes like this. Right now there are private companys as well as our government looking to make a motor/generator for use in 3rd world countries and probably military use. The idea is to use a 3-phase brushless DC motor to spin up a small turbine engine so that they can be started. Typically 30,000 + rpm. Meter in whatever fuel you got laying around, say propane. Viola, you now have an operational turbine. Now, use the starter motor as a 3 phase generator. You now have lots of available power. I was working with a company that was Engineering a 3 phase brushless for just this task. I thought it would be a great idea for car audio needs. Alas, the price is quite steep. The gentleman and I went on to discuss the application of doing it with an alternator. Most of the car audio SMPS I had a hand in were mostly operated at under 40 kHz. Switching losses in the ferrite core and the MOSFET drivers almost make you keep your frequency low. The higher the frequency, the higher the losses, especially in high current supplies. There is also higher noise induced when the rectifying diodes conduct and recovers as frequency increases. Where I used to work, we did make 1 or 2 smaller amplifiers that were switching at 60-80 kHz. They worked quite well. I have seen poorly designed amplifiers that you can indeed hear the sum and difference beating of the audio/SMPS. We called it "swizzle" I personally would like to make a power supply using IGBT's switching at 75 kHz or higher. It will also take a better grade of ferrite for the core matl. Good info, John Andreen "David R Brooks" wrote in message ... For *real* B+ power in a car, why not a 3-phase transformer fed direct from the alternator? Robert Casey wrote: [snip] :But you need to have a DC-DC converter from 12V to the B+ you need at the :current you need. A switchmode supply operating around 100KHz frequency to avoid noise in the audio, also no beat frequencies from audio and 100KHz :invading the audio spectrum). |
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Thanks for the info,
I checked the schematic, there are 8 pairs of complementary sets. I have decided that I will post at least the output section of the schematic. I have to scan in from paper and do recognition. Clean it up a bit to remove any bits that might cause legalities. That way you all can have a look and see. Okay? I am an Engineer and not to afraid to share knowledge and ideas. I guess that is really what a forum is all about. I have however worked with those who would not tell another a single thing. Shouldn't be more than a few days before I post it. Any ideas on how to do this properly? Should I place it on my personal web space and provide a pointer? About the schematic, I still don't understand just what configuration the output drivers are in. When I get it up there maybe someone can tell me. SS is butter to me, Valves are still a conondrum. Regards, John Andreen "Robert Casey" wrote in message ... John Andreen wrote: Patrick, Thanks again for all the wonderful insight. I would love to provide a schematic, but I do not know the legalities involved. It is in fact intellectual property of a rather large audio company. They have deep pockets and mean lawyers. Trust me on this, I know whom they have litigated and sent into the depths of oblivion. I was only given a copy of the schematic out of friendship and on the condition that I won't reveal it. It could also compromise my friend and his position. As a side note, this companies Non-Disclosure agreement is 28 pages of legalistic mumbo jumbo and folderol. I can however, publish a schematic of my modified design when I am completed or near completion. I must be able to show that this is my own design, complete with a minimum of 7 unique differences. This is really why I am asking some of the questions that I ask. Slowly but surely identifying the *major* design flaws and then creating my own circuits to hopefully correct them. I may know much about silicon audio, but I am for sure a plebe at vacuum tubes. When I get home, I will check the schematic and count the output devices. Just from memory, I am certain that there are at least 6 sets of complementary pairs. Car audio is really a harsh environment to design for( this is not the case for my design, as I want to drive my Apogee's at home). Most output devices are operated at a maximum heatsink temperature of about 90 degrees C. So taking into account device derating, it is rather common to use an excess of output devices. And, in a car, it could be in Gnome, Alaska one day and in Death Valley the next. Currently, I am still working on the PS sections. This includes the tube heaters, the +/- 300 volt rails for the tubes, +/- 18 volt rails for the rails for the output BJT's, and the +/- 15 volt rails for the support circuitry. Haven't made it to the audio sections yet. Hell, I am still having a tough time understanding that there is only 1 kind of tube and not P and N tubes like transistors. There's the quasi-complementary style circuit, with two tubes stacked totem pole style. Something like http://headwize2.powerpill.org/proje...=cmoy5_prj.htm figure 1 You could change things so the bottom tube's cathode circuit is fed by a negative power supply, and the top tube's plate circuit fed by a positive power supply. And the top tube's grid tied to ground thru a 500K resistor. You wouldn't use this exact circuit, as you want more power and low impedance. But this topology should suggest possibilities. |
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On Tue, 21 Oct 2003 21:12:00 -0700, the highly esteemed John Andreen
enlightened us with these pearls of wisdom: snip About the schematic, I still don't understand just what configuration the output drivers are in. When I get it up there maybe someone can tell me. SS is butter to me, Valves are still a conondrum. The best analogy to SS for a tube is an n-channel depletion mode JFET. Electrode-wise, source=cathode, drain=plate(or anode), and gate=grid. Tetrodes and pentodes also have a screen grid, which has no SS equivalent, and pentodes also have a suppressor which may or may not be internally connected (it is in most, but not all pentodes). Again, these have no true SS equivalent. However, as far as circuit configurations the screen and suppressor do not usually influence its type (unless it is used as a control electrode - normally they are used at a fixed potential). The above being the case, you can use a tube in any circuit which you can use an n-channel depletion mode JFET. This includes common cathode, common grid, common plate (cathode follower) for a simple single-device configuration. Multiple devices can be cascades, cascodes, differential pairs, etc. If you want to post your schematic to a newsgroup, don't do it here. The "official" place is alt.binaries.schematics.electronic (you will sometimes see the acronym ABSE, which refers to that group). Otherwise, putting it on a website and posting the URL here is fine as well. -- Greg --The software said it requires Win2000 or better, so I installed Linux. |
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Thanks for all the help,
I think I will place the schematic on my homepage/website. Gotta set it up first as I am a new subscriber to cox hi speed internet. Maybe I will just place it in my "space" and point to it. Almost done with cleaning it up so that I can post it. Smart man you are running Linux. It is by far and away my most favorite OS. Mac's are next, though my 7710/180 is outdated and won't run OSX without processor card. Sadly, I am writing this on WinXP. Regards, John Andreen "Greg Pierce" wrote in message news On Tue, 21 Oct 2003 21:12:00 -0700, the highly esteemed John Andreen enlightened us with these pearls of wisdom: snip About the schematic, I still don't understand just what configuration the output drivers are in. When I get it up there maybe someone can tell me. SS is butter to me, Valves are still a conondrum. The best analogy to SS for a tube is an n-channel depletion mode JFET. Electrode-wise, source=cathode, drain=plate(or anode), and gate=grid. Tetrodes and pentodes also have a screen grid, which has no SS equivalent, and pentodes also have a suppressor which may or may not be internally connected (it is in most, but not all pentodes). Again, these have no true SS equivalent. However, as far as circuit configurations the screen and suppressor do not usually influence its type (unless it is used as a control electrode - normally they are used at a fixed potential). The above being the case, you can use a tube in any circuit which you can use an n-channel depletion mode JFET. This includes common cathode, common grid, common plate (cathode follower) for a simple single-device configuration. Multiple devices can be cascades, cascodes, differential pairs, etc. If you want to post your schematic to a newsgroup, don't do it here. The "official" place is alt.binaries.schematics.electronic (you will sometimes see the acronym ABSE, which refers to that group). Otherwise, putting it on a website and posting the URL here is fine as well. -- Greg --The software said it requires Win2000 or better, so I installed Linux. |
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