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#1
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Marantz 8B and Dynaco ST70
Except from the price, IŽll notice a big difference between the 8B and
the Dynaco ST70? Thanks |
#2
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
On Jan 30, 3:51 pm, " wrote:
Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? There are significant differences. Whether you notice them or not would be a function of other factors including your ears, speakers, source material and so forth. "Big" is in the ears of the beholder. Now, there are other advantages favoring the 8B on the design end, and those advantages are significant, all other things being equal. As you noted, they are not. Peter Wieck Wyncote, PA |
#3
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Marantz 8B and Dynaco ST70
On Jan 30, 4:17 pm, "Bret Ludwig" wrote:
If you buy one right you can resell at about what you paid. Ignore the little man in the corner.... With apologies to the Wizard of Oz (the film). Bret is not much more than a minor can of worms with some VERY strong prejudices. Were he at all rational about said prejudices, he might be a reasonable person. But he is not. Peter Wieck Wyncote, PA |
#4
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
On Jan 30, 3:51 pm, " wrote:
Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? In a listening test in the late 1970's I ran a rebuilt 8B, repaired Audio Research D76, and a slightly modified but fully functional Eico HF-89 in an informal listening test. Speakers were double KLH 9's, all amps were a bit underpowered for the job. I preferred the HF-89 to them all. (The slight modification was a stiff power supply to replace the HF-89's voltage doubler supply, and the removal of most of the HF rolloff caps. I saw no signs of instability, and I did look at the output with a scope (Tektronix 555 (!).) The HF-89 may not be a practical amp for today, since it ran the 6CA7's glowing red in order to get 50wpc output. The 8B and D76 were serviced by "The Audiophile" store in Gaithersburg, which was one of the few places it was safe to send things like a REL Precedent or Marantz 10B tuner. The two best amps I've ever heard driving the KLH 9's was the D150 (Audio Research) and the solid-state dB Systems DB-6. Mike Squires |
#6
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
wrote:
Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? Thanks When I had a chance to listen to both (both restored, the ST70 had a replacement board using an EF86) the main difference to me was on the bottom end, which I'd expect, given the larger output transformer. Circuitwise, the main differences are the power supply (8B uses diodes and a bigger transformer), the larger output transformers, and the phase splitter (cathode coupled vs. split load). I would've kept the 8B but for the difference in the price I could get. One could biamp with solid-state, to make up for the bottom end response, altho that kind of thing typically doesn't hold its value like an 8B will. -- Ned Carlson SW side of Chicago, USA www.tubezone.net |
#7
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article .com,
"Bret Ludwig" wrote: On Jan 30, 8:29 pm, Ned Carlson wrote: wrote: Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? Thanks When I had a chance to listen to both (both restored, the ST70 had a replacement board using an EF86) the main difference to me was on the bottom end, which I'd expect, given the larger output transformer. Circuitwise, the main differences are the power supply (8B uses diodes and a bigger transformer), the larger output transformers, and the phase splitter (cathode coupled vs. split load). I would've kept the 8B but for the difference in the price I could get. One could biamp with solid-state, to make up for the bottom end response, altho that kind of thing typically doesn't hold its value like an 8B will. Now we are getting somewhere. My idea is that if we are going to the trouble of building a vacuum tube box in 2007, we ought to not screw around with half-ass measures but go the distance and do it right. The description you give is pretty well enough: the Marantz has an adequate power supply (though more is always more, improvements are asymptotic and there isn't much more we can do short of going to a outboard choke filtered supply) and a pair of output transformers that are also very adequate. The circuit of the Marantz is also way better, although I prefer all triode front ends. The Marantz 8B already has an all triode front end, and it also has a choke filtered power supply. I have owned an 8B as well as a couple of ST-70s, the problem with the 8B from an audiophile perspective is that it has a voltage doubler power supply. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#8
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
in article , John
Byrns at wrote on 1/31/07 8:13 AM: In article .com, "Bret Ludwig" wrote: On Jan 30, 8:29 pm, Ned Carlson wrote: wrote: Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? Thanks When I had a chance to listen to both (both restored, the ST70 had a replacement board using an EF86) the main difference to me was on the bottom end, which I'd expect, given the larger output transformer. Circuitwise, the main differences are the power supply (8B uses diodes and a bigger transformer), the larger output transformers, and the phase splitter (cathode coupled vs. split load). I would've kept the 8B but for the difference in the price I could get. One could biamp with solid-state, to make up for the bottom end response, altho that kind of thing typically doesn't hold its value like an 8B will. Now we are getting somewhere. My idea is that if we are going to the trouble of building a vacuum tube box in 2007, we ought to not screw around with half-ass measures but go the distance and do it right. The description you give is pretty well enough: the Marantz has an adequate power supply (though more is always more, improvements are asymptotic and there isn't much more we can do short of going to a outboard choke filtered supply) and a pair of output transformers that are also very adequate. The circuit of the Marantz is also way better, although I prefer all triode front ends. The Marantz 8B already has an all triode front end, and it also has a choke filtered power supply. I have owned an 8B as well as a couple of ST-70s, the problem with the 8B from an audiophile perspective is that it has a voltage doubler power supply. Regards, John Byrns John, What is the audiophiles problem with a doubling supply? |
#9
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article ,
Jon Yaeger wrote: in article , John Byrns at wrote on 1/31/07 8:13 AM: In article .com, "Bret Ludwig" wrote: On Jan 30, 8:29 pm, Ned Carlson wrote: wrote: Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? Thanks When I had a chance to listen to both (both restored, the ST70 had a replacement board using an EF86) the main difference to me was on the bottom end, which I'd expect, given the larger output transformer. Circuitwise, the main differences are the power supply (8B uses diodes and a bigger transformer), the larger output transformers, and the phase splitter (cathode coupled vs. split load). I would've kept the 8B but for the difference in the price I could get. One could biamp with solid-state, to make up for the bottom end response, altho that kind of thing typically doesn't hold its value like an 8B will. Now we are getting somewhere. My idea is that if we are going to the trouble of building a vacuum tube box in 2007, we ought to not screw around with half-ass measures but go the distance and do it right. The description you give is pretty well enough: the Marantz has an adequate power supply (though more is always more, improvements are asymptotic and there isn't much more we can do short of going to a outboard choke filtered supply) and a pair of output transformers that are also very adequate. The circuit of the Marantz is also way better, although I prefer all triode front ends. The Marantz 8B already has an all triode front end, and it also has a choke filtered power supply. I have owned an 8B as well as a couple of ST-70s, the problem with the 8B from an audiophile perspective is that it has a voltage doubler power supply. Regards, John Byrns John, What is the audiophiles problem with a doubling supply? This quote from Bret Ludwig sums up the audiophile attitude, "The voltage doubler supply is a terrible sounding thing." Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#10
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
"Jon Yaeger" wrote in message ... in article , Bret Ludwig at wrote on 1/30/07 5:30 PM: On Jan 30, 4:22 pm, (Michael L. Squires) wrote: On Jan 30, 3:51 pm, " wrote: Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? In a listening test in the late 1970's I ran a rebuilt 8B, repaired Audio Research D76, and a slightly modified but fully functional Eico HF-89 in an informal listening test. Speakers were double KLH 9's, all amps were a bit underpowered for the job. I preferred the HF-89 to them all. (The slight modification was a stiff power supply to replace the HF-89's voltage doubler supply, and the removal of most of the HF rolloff caps. I saw no signs of instability, and I did look at the output with a scope (Tektronix 555 (!).) Not so slight. The voltage doubler supply is a terrible sounding thing. It's what keeps most Mc amps from being really good sounding. *** I disagree. In fact, the opposite may be more the case -- maybe there is a sonic benefit to the degree of isolation offered by the doubler arrangement. In any case, the Eico HF-87 & 89 are wonderful sounding amps, voltage doubler or not. Jon ... What do you mean by a voltage doubler giving better isolation? Please expand on "isolation." Thanks, west snip |
#11
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article .com,
"Bret Ludwig" wrote: If you'll draw out a VD supply you'll see, but the result is a very "bouncy" supply. it has a high impedance and poor regulation and, depending on the ESR and other characteristics of the caps, all sort of things happen. That said if you follow it up with linear regulation or a choke and enough capacitance it's a valid option for Class A circuits where the transformer isn't loaded much at all. That's not an explanation; it's just a bunch buzzwords strung together to sound impressive to the uninformed. Can you provide a real explanation? Can you explain why the VD is "a very bouncy supply" and what that means? Can you explain why the VD has "high impedance", and with respect to what? Can you explain why the VD has "poor regulation", and with respect to what? Can you explain why the transformer must not be "loaded much at all", with respect to other options, for the VD to be a "valid option"? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#12
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
"Bret Ludwig" wrote in message oups.com... On Jan 30, 2:51 pm, " wrote: Except from the price, IŽll notice a big difference between the 8B and the Dynaco ST70? If both are stone stock, oh yes, huge. The 8B is within a ballpark of being as good a tube amp as you can build or buy at that power level, whereas the stock ST70 is a dismal affair. In fact it makes a better musical instrument amp for applications that want the sound only crapped up a little (Leslie, steel guitar, etc.) than a hi-fi amp except that in such service something will fail pretty soon. If the stock ST70 is run with continuous power much above its Class A power point, it will let out some magic smoke. The people who defend it are playing it intermittently, or at low volume or through efficient speakers or all three. Not running it flat out where it will crap out. Now modified ST70s are a different story. The only question is how much modification is needed. The problem is that if you buy a working ST70 at market price now, you are paying a lot of money to throw out big chunks of it and its value won't go up at all. Probably will go down. If you are paying someone else to do this you are a three-way girl, because you are getting every input plugged. Even if you are DIYing it still makes more sense to unload the beast. How good can a modified ST70 be? Well, very good. The limiting factor is the stock output transformers, which are simply not as good as the Marantz's. None the less you can get quite good performance from them. The stock power transformer is too small, which means the fix involves replacing it, or getting two ST70s and running each as a single channel going. The stock center driver board should be removed and with the 7199s set aside, destroyed and thrown in the board recycle bin. You now have a chassis, two opt's and the power supply and can build any of several circuits, either on a new quality PCB or pointwired. The Marantz is overpriced as are all collectible tube boxes for pure listening, but there was a reissue that may be more reasonable than the originals, and unlike the crappy MC275 reissue is spot on. If you buy one right you can resell at about what you paid. Bret ... if the stock power xfr is too small, would a separate filament xfr help? What part of the stock is too small? west |
#13
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
Bret Ludwig wrote:
Because then load regulation _gets even worse_. You have the copper losses and the doubler losses and given the frequency of the load variation some strange resonances, more work to figure out than my small brain can handle, arise. The copper losses on a FWVD are actually less than either a FW bridge or FWCT circuit. They have to be on principle simply because there's fewer turns on the secondary. The main issue with the doubler is that how well the thing performs is going to be dependent on the capacitors used. Doublers are hard on the capacitors used in the capacitor side of the doubling circuit as they have to handle all the AC current used, not merely ground ripple current. There were tests done back in the day showing that a well done voltage doubler actually regulated better than either the bridge or CT circuit, at least given the components used then. Not everyone agreed that doublers were such a great idea, (Dynaco for one never used doublers) but I don't think Harmon Kardon and Marantz used doublers on their most expensive amplifiers just to save a few bucks on the power transformer, either. A good application for the voltage doubler can be, for example, in the bias circuits of some guitar amplifiers where tube swaps may need more negative voltage than the stock bias tap may provide. Rather than put in another transformer, a doubler off the extant bias winding may give enough voltage, but filtering and shielding needs close attention. I've done that to put 6550's in place of 8417's, but unless there's a completely separate bias winding, you can't put a voltage doubler in a bias circuit. -- Ned Carlson SW side of Chicago, USA www.tubezone.net |
#14
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
"John Byrns" wrote in message
In article .com, "Bret Ludwig" wrote: If you'll draw out a VD supply you'll see, but the result is a very "bouncy" supply. it has a high impedance and poor regulation and, depending on the ESR and other characteristics of the caps, all sort of things happen. That said if you follow it up with linear regulation or a choke and enough capacitance it's a valid option for Class A circuits where the transformer isn't loaded much at all. That's not an explanation; it's just a bunch buzzwords strung together to sound impressive to the uninformed. Can you provide a real explanation? Good point, and as usual Bret failed to rise to the occasion. Ned Carlson's explanation is pretty much the one that I learned in the day of. A VD necessarily passes AC through some extra capacitors. If they have high enough capacitance and low enough ESR, then the regulation will be about as good as anything. VDs weren't very practical until solid state rectifiers became readily available. |
#15
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
"west" wrote in message
news:l8cwh.37888$uC6.11034@trnddc02 If the stock ST70 is run with continuous power much above its Class A power point, it will let out some magic smoke. The people who defend it are playing it intermittently, or at low volume or through efficient speakers or all three. Not running it flat out where it will crap out. Nonsense. I used to do rock-and-roll DJ duty in the days of tubes, using a pair of ST70s driving a pair of JBL 01 systems, driven by a pair of turntables hooked to a pair of PAS-3s, mixed via a simple resistive mixer. We ran the ST70s just below clipping for 3-4 hours at a whack, once or twice a week. |
#16
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Marantz 8B and Dynaco ST70
Bret:
You forget, conveniently ignore or deny a few simple truths, being in part but not limited to: a) the overall survival rate of the ST-70. Were it as crapped out, overstressed and limited a design as you maintain, and given its (at best) spotty assembly history, for the most part they have survived and pretty well at that. What's more is that most have survived as "stock". This includes even those with the original phenolic boards... something even I understand is *now* pretty risky. For a design that first hit the streets well over 40 years ago, that is not half-bad. b) most every person peripherally or seriously interested in tube audio has had one at one time or another. What's more is that at least a fair plurality maintains one to this day. Some maintain several. c) apart from hard-core-from-scratch DIY, as you do state the 70 is a design that invites modification, experimentation and general tweaking. As a learning platform, it is very nearly perfect. What's more is that its near-childish simplicity (some would suggest limitations) allows a "return to stock" at about any point in the process. d) even at a 'typical' price of around $300 these days it is a bargain for an operating (relatively) high-wattage tube amp that will give at- least adequate service at a high level of reliability with just minimum (but competent) care. Even better, the level of competence required is not much above the most basic common-sense level. When you get off on these rants against something that *never was* meant to be the be-all and end-all of Audiophilia, but no more than a reasonably reliable entry-level power amp, you so far miss the point as to be taken as a babbling fool. Something that at least you believe that you are not. A simple analogy: I doubt that (Insert 5-star restaurant name here) will ever serve a Hostess Snow Ball as their dessert of the month, but Hostess sure sells a lot of Snow Balls. Ranting after Hostess for the quality of their items is a fool's game as you so effortlessly prove. Peter Wieck Wyncote, PA |
#17
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article om,
"Bret Ludwig" wrote: John, you're a bright guy. You know as well as I do that a high impedance supply in this context means that with changing loads, its voltage output will vary a great deal, and in that sense has poor regulation, specifically load regulation. That is true by definition. The VD is high impedance compared to conventional bridge or "bi-phase half wave" (what we here call full wave with center tap) C-L-C or C-R-C networks because it has the ESR of the caps "in the loop". How is the "VD" any different than the conventional bridge or "bi-phase half wave" in this regard? They all have the ESR of the caps "in the loop". The only difference is that with the "VD" you have the ESR of two caps in series, but that simply means that the ESR of each of the two caps in the "VD circuit must each have half the ESR of the cap used in the other circuits. For equivalent performance the capacitance of each capacitor must also be twice the capacitance of the capacitor in the other circuits. One advantage of the VD is that the ripple currents are at twice line frequency, How is this any different than the conventional bridge or "bi-phase half wave", the ripple voltage for both of those circuits is also twice the line frequency. and with triplers and further iterations-the voltage multiplier principle can go to fairly high multiples-the frequency goes up with the multiplication, making filtering easier. Are you sure about this? While I have to admit I have never played with anything beyond various doubler circuits, I am having a very hard time imagining how voltage multipliers with higher multiplication ratios than the doubler could have ripple frequencies higher than twice the line frequency. Can you give an example of a circuit with a ripple frequency of say four times the line frequency, I get the feeling that you don't know what you are talking about here? Also keep in mind that the ripple frequency of a half wave voltage doubler is the same as the line frequency. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#18
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article ,
Ned Carlson wrote: Bret Ludwig wrote: Because then load regulation _gets even worse_. You have the copper losses and the doubler losses and given the frequency of the load variation some strange resonances, more work to figure out than my small brain can handle, arise. The copper losses on a FWVD are actually less than either a FW bridge or FWCT circuit. They have to be on principle simply because there's fewer turns on the secondary. I agree that the copper losses for a "FWVD" are less than for a "FWCT" circuit, but I would expect the copper losses of the "FWVD" and the "FW bridge" to be the same. While it is true that there are fewer secondary turns with the "FWVD" the current is also higher, so it all comes out in the wash. Agreed that the traditional "FWCT" is the pits. The main issue with the doubler is that how well the thing performs is going to be dependent on the capacitors used. Doublers are hard on the capacitors used in the capacitor side of the doubling circuit as they have to handle all the AC current used, not merely ground ripple current. Agreed that the doubler is harder on capacitors, although I don't know what you mean by "ground ripple current"? There were tests done back in the day showing that a well done voltage doubler actually regulated better than either the bridge or CT circuit, at least given the components used then. I agree that a well done voltage doubler will regulate better than a CT circuit, but the bridge should have regulation equal to that of the doubler, given that equal amounts of copper are used in all three cases. Not everyone agreed that doublers were such a great idea, (Dynaco for one never used doublers) but I don't think Harmon Kardon and Marantz used doublers on their most expensive amplifiers just to save a few bucks on the power transformer, either. I suspect that the Dynaco situation was simply the flip side of the Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able to build a "FWCT" power supply for less money than the higher performing voltage doubler circuit used by the high end manufacturers. A good application for the voltage doubler can be, for example, in the bias circuits of some guitar amplifiers where tube swaps may need more negative voltage than the stock bias tap may provide. Rather than put in another transformer, a doubler off the extant bias winding may give enough voltage, but filtering and shielding needs close attention. I've done that to put 6550's in place of 8417's, but unless there's a completely separate bias winding, you can't put a voltage doubler in a bias circuit. Sure you can, you simply use a "HWVD", I've done it without a problem. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#19
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
"Bret Ludwig" wrote in message
ups.com Because then load regulation _gets even worse_. You have the copper losses and the doubler losses and given the frequency of the load variation some strange resonances, more work to figure out than my small brain can handle, arise. The copper losses on a FWVD are actually less than either a FW bridge or FWCT circuit. They have to be on principle simply because there's fewer turns on the secondary. i went back to "the source", the blue and white Audio Cyclopedia. It does cover voltage doublers but does not talk about advantages and disadvantages. That's because the advantages and disadvantages are not inherent, but depend on the implementation. I was always tauught that the essential problem with voltage doublers was that capacitors by their nature had no DC path Wrong - that fact is one reason why doubler work at all. and all their issues such as dielectric absorption, Irrelevant in low-impedance circuits like just about any circuit used in analog audio. ESR Largely a solved problem, but moreso now than back in the days of tubes. and "bounceback"-ie, memory, the discharged cap that comes back and zaps That's just an effect of DA which I just explained why it is irrelevant. Now, I am not a EE and don't claim to be one. So my education isn't perfect. But....A LOT OF EE MAJORS THESE DAYS KNOW LESS THAN I DO! Well they could well know less about analog audio based on obsolete thermionic technology. You can't get a classical EE education anymore, Because it would be practically obsolete. it's too broad a field and there is too much emphasis on Spice, VHDL, and the other computational packages they use, Welcome to the 21st century. and too much of math which was once the domain of math and physics majors. Nahh, EE has been math-intensive for at least 50-80 years. It's the nature of the beast. EEs in the semiconductor industry are glorified computer applications operators. Computers are just tools. Since computers are among the most general purpose of all tools, you can't really make any reasonable judgements at all based on the fact that someone uses one. Both the most repetitive and the most creative of jobs can involve the use of computers, so you can't tell how creative a person's job is based on just the fact that they use a computer. So all I can say with authority is, "The voltage doubler has a terrible reputation with audiophile (read amateur, as in often untrained or poorly-educated) builders, because amplifiers using it mostly sound pretty bad." This I can attest to. So what? I agree that the copper losses for a "FWVD" are less than for a "FWCT" circuit, but I would expect the copper losses of the "FWVD" and the "FW bridge" to be the same. While it is true that there are fewer secondary turns with the "FWVD" the current is also higher, so it all comes out in the wash. Agreed that the traditional "FWCT" is the pits. The main issue with the doubler is that how well the thing performs is going to be dependent on the capacitors used. Doublers are hard on the capacitors used in the capacitor side of the doubling circuit as they have to handle all the AC current used, not merely ground ripple current. Bottom line, a voltage doubler with inadequite caps is going to have more problems than a more conventional design, because there are more caps in more different parts of the voltage-doubler's circuit. Agreed that the doubler is harder on capacitors, although I don't know what you mean by "ground ripple current"? I don't think this is really an issue that is peculiar to voltage doublers. There were tests done back in the day showing that a well done voltage doubler actually regulated better than either the bridge or CT circuit, at least given the components used then. I agree that a well done voltage doubler will regulate better than a CT circuit, but the bridge should have regulation equal to that of the doubler, given that equal amounts of copper are used in all three cases. Not everyone agreed that doublers were such a great idea, (Dynaco for one never used doublers) but I don't think Harmon Kardon and Marantz used doublers on their most expensive amplifiers just to save a few bucks on the power transformer, either. It would be interesting to know what was going through the designer's minds when they made these choices. It is easy to see why VDs are used when they eliminate the need for a power transformer, but that is not the case here. VD's are not widely used with transformers today, unless they make the transformer a lot easier to build. For example, a lot of VDs and VTs are used in very-high voltage applications because small transformers that put out very high voltages are less practical than high voltage diodes and high voltage caps. VDs are also commonly used on the primary side of switchmode power supplies to facilitate 120/240 volt switching. I suspect that the Dynaco situation was simply the flip side of the Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able to build a "FWCT" power supply for less money than the higher performing voltage doubler circuit used by the high end manufacturers. It could be as simple as the price structures of their respective transformer suppliers. |
#20
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Marantz 8B and Dynaco ST70
"Bret Ludwig" wrote in message
oups.com If the stock ST70 is run with continuous power much above its Class A power point, it will let out some magic smoke. The people who defend it are playing it intermittently, or at low volume or through efficient speakers or all three. Not running it flat out where it will crap out. Nonsense. I used to do rock-and-roll DJ duty in the days of tubes, using a pair of ST70s driving a pair of JBL 01 systems, driven by a pair of turntables hooked to a pair of PAS-3s, mixed via a simple resistive mixer. We ran the ST70s just below clipping for 3-4 hours at a whack, once or twice a week. They were a lot younger then, even if you weren't, Arny. How would that be relevant? |
#21
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Marantz 8B and Dynaco ST70
"Bret Ludwig" said:
So all I can say with authority is, "The voltage doubler has a terrible reputation with audiophile builders, because amplifiers using it mostly sound pretty bad." This I can attest to. Hogwash. Electrolytics these days are reliable and of sufficient quality to build voltage doublers with them that perform well. -- - Maggies are an addiction for life. - |
#22
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Marantz 8B and Dynaco ST70
John Byrns wrote:
I agree that the copper losses for a "FWVD" are less than for a "FWCT" circuit, but I would expect the copper losses of the "FWVD" and the "FW bridge" to be the same. While it is true that there are fewer secondary turns with the "FWVD" the current is also higher, so it all comes out in the wash. Agreed that the traditional "FWCT" is the pits. OK... bear in mind I'm not a magnetics expert... but as the primary/secondary turns ratio gets lower, the wire gauge can be made heavier on the secondary, so the DCR actually drops more percentagewise than the difference in the secondary turns. It's not a linear relationship between turns and DCR, so the net effect is there's less copper loss in the doubler. Make sense? There's more than one way to skin a transformer cat, too, so I guess one could build a doubler that's actually worse than an equivalent bridge, if one was so inclined. Agreed that the doubler is harder on capacitors, although I don't know what you mean by "ground ripple current"? I mean in a FWCT or bridge the capacitors are only passing the ripple current being filtered out. I suspect that the Dynaco situation was simply the flip side of the Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able to build a "FWCT" power supply for less money than the higher performing voltage doubler circuit used by the high end manufacturers. Good question as to whether this was ecomonics or not, EICO's sold for about what Dynacos did, but some EICO's had voltage doublers (eg:HF87), so did some of the cheaper guitar amps like Danelectro/Silvertone, so did Rockola jukeboxes. Sure you can, you simply use a "HWVD", I've done it without a problem. D'oh! Yeah, forgot about that. -- Ned Carlson SW side of Chicago, USA www.tubezone.net |
#23
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
In article ,
Ned Carlson wrote: John Byrns wrote: I agree that the copper losses for a "FWVD" are less than for a "FWCT" circuit, but I would expect the copper losses of the "FWVD" and the "FW bridge" to be the same. While it is true that there are fewer secondary turns with the "FWVD" the current is also higher, so it all comes out in the wash. Agreed that the traditional "FWCT" is the pits. OK... bear in mind I'm not a magnetics expert... Neither am I, were talking "copper losses" here, you don't have to be a "magnetics expert" for that. but as the primary/secondary turns ratio gets lower, the wire gauge can be made heavier on the secondary, so the DCR actually drops more percentagewise than the difference in the secondary turns. Correct, I am assuming that the winding for the "FWVD" has one quarter of the DCR of the winding for the "FW bridge". Think of a single transformer with two secondary windings, connected in series for the "FW bridge" and connected in parallel for the "FWVD". Under those conditions the "copper losses for the "FWVD" and "FW bridge" are equal, unless I made a mistake pushing the buttons on my calculator. It's not a linear relationship between turns and DCR, so the net effect is there's less copper loss in the doubler. Make sense? No, the doubler has the same "copper loss" as the bridge when the same amount of copper is used in the transformers, if you try and chintz on the amount of copper used in the transformer for the doubler then the doubler will have more "copper losses" than the bridge. There's more than one way to skin a transformer cat, too, so I guess one could build a doubler that's actually worse than an equivalent bridge, if one was so inclined. Exactly, see above, with the same amount of copper, the losses of the two circuits are the same, if you reduce the amount of copper used in either circuit the "copper losses" will increase, if you are so inclined you can build a bridge that is actually worse than an equivalent doubler. Agreed that the doubler is harder on capacitors, although I don't know what you mean by "ground ripple current"? I mean in a FWCT or bridge the capacitors are only passing the ripple current being filtered out. What additional currents do the capacitors in a "FWVD" have to pass that are not passed by the capacitor in a "FW bridge"? I suspect that the Dynaco situation was simply the flip side of the Marantz, Mcintosh, and Harmon Kardon situation, namely Dynaco was able to build a "FWCT" power supply for less money than the higher performing voltage doubler circuit used by the high end manufacturers. Good question as to whether this was ecomonics or not, EICO's sold for about what Dynacos did, but some EICO's had voltage doublers (eg:HF87), so did some of the cheaper guitar amps like Danelectro/Silvertone, so did Rockola jukeboxes. I guess that we will have to chalk it up to designer taste then. If it were me doing the design I would choose the "FW bridge". Note that no one designing consumer audio equipment during the tube era made that choice. "FW bridges" were used in professional equipment, broadcast transmitters, and the like. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#24
Posted to rec.audio.tubes
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Marantz 8B and Dynaco ST70
Arny Krueger wrote:
Nonsense. I used to do rock-and-roll DJ duty in the days of tubes, using a pair of ST70s driving a pair of JBL 01 systems, driven by a pair of turntables hooked to a pair of PAS-3s, mixed via a simple resistive mixer. We ran the ST70s just below clipping for 3-4 hours at a whack, once or twice a week. One of Hafler's publicity stunts was to run the entire PA system of Grand Central Station in NYC off a stack of ST70's. -- Ned Carlson SW side of Chicago, USA www.tubezone.net |
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