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    Running Khorns off the 4 ohm tap

    Those are good articles. But in fact, the "actual damping factor" defined in the Augspurger article is itself still an over-estimate of the damping. He correctly adds the DC resistance of the voice coil to the amplifier output impedance, to make the quantity in the denominator in his...
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    Damping Factor

    The damping factor, as conventionally defined, is a very misleading term. It is conventionally taken to be the speaker impedance divided by the output impedance of the amplifier, and so with an 8 ohm speaker and an amplifier with very low output impedance (let's say 0.05 ohms, for example), one...
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    Schematic speaker symbol? Negative?

    I would guess that it is denoting the polarity of the loudspeaker, in the sense that (for example), if the marked speaker terminal is at positive voltage relative to the other terminal, then it corresponds to the cone moving outwards. So two speakers connected the same way around will both have...
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    Uluru: Photon-Coupled SEPP Triode Amplifier Project

    "Has anyone seen any other designs that use a (-) rail like this?" It's the standard way a totem-pole OTL is constructed.
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    Power cord question

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    Power cord question

    The trouble with many of the anecdotes where someone reports that an expensive power cord improved the sound is that there seems to have been a lack of curiosity as to why it made a difference. If there was a buzzing noise with one cord, and no buzzing with another, then there are some very...
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    Power cord question

    Perhaps, just conceivably, a shielded power cord could help to suppress not only RFI around the cord itself, but also RFI entering into it from the unshielded house wiring, by virtue of it effectively providing a bit of capacitance between the cable and ground, thus creating a low-pass filter...
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    Power cord question

    I have tilted at the power-cord windmill and many other similar "audiophile" issues for years now, but unfortunately one never gets anywhere. The power of suggestion, and experimenter-expectancy, is strong, and no amount of logic, argument about the likely orders of magnitude of physical...
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    Power cord question

    One of the curious discoveries in high-end audio is that the "bits you can reach" seem to have much more effect on the sound than the bits you can't reach. Thus for example the power cord affects the sound, but the miles of AC power lines coming to your house from the generating station, and...
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    My take on a Single Ended amp

    Thanks. That is very helpful, and resolves my puzzle!
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    My take on a Single Ended amp

    Yes, but in a single-ended amplifier, surely pushing the power to the point where the tube is cutting off at the bottom of the audio cycle means you have pushed to the point of clipping, and appalling distortion? Coming back to the issue of the power supply sag, isn't it the case that the...
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    My take on a Single Ended amp

    I was slightly surprised when you mentioned substantial power-supply sag at full power. Is that really a significant issue? In class A in the ideal case, the average current demand on the power supply (i.e. average over audio cycle) is independent of the audio power level. Of course an actual...
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    Luxman MQ-36 OTL.. is this thing safe (circuit)?

    Maybe looks as if it was pulled from an old solid state amp design book, but actually it's the other way around. The output configuration is of the totem pole type, which dates back at least to July 1953 (J. Futterman's patent) in the context of OTL amplifiers driving low impedance speakers...
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    Capacitors: Characteristics, Series, Parallel, limits, etc

    You seem to be saying that when there is no audio signal, the tube is passing "little to no current," or just a "trickle." This is really not true. The quiescent current in the output tubes of a typical push-pull amplifier is a lot more than "a trickle." It is typically enough to represent a...
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    Capacitors: Characteristics, Series, Parallel, limits, etc

    Why do you say no current flows when there is no audio signal? In an audio amplifier, the tubes are always biased so that there is some quiescent cathode-anode current, even in the absence of an audio signal.
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    Why electrolytics in power supply

    I think the final capacitors in the power supply are very much "in the audio path." I am not one to argue for boutique capacitors, or any nonsense like that, but I think one definitely should bear in mind that the audio signal passes through those capacitors, and so one needs to make sure, one...
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    Are these two tubes the same one?

    "I don't see the Mullard production code (or whatever the 1282 H1 printing is) on the first one. Possibly they are twins, but not the same individual tube" I assumed the proposition under discussion was that some devious seller might have scraped off some markings (Pope) and added others (1282...
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    Are these two tubes the same one?

    "Not hard to believe. If you look at a rubber stamp, every little crack will show where the ink cannot sit." Well obviously, yes, the broad structure of flaws will be the same in all printings. What I had in mind, though, is that the printing seems to have been done with some fairly goopy kind...
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    Are these two tubes the same one?

    I'm not too familiar with how similar the printing from a particular die will look on different tubes, but there do seem to be sufficiently many flaws in the printing in common in the two pictures that it is hard to believe they could be different tubes. For example, the "nick" near the upper...
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    Still looking for solution-one source to 4 tube amps

    Just curious, what you mean by "...it soon developed a hum..." You mean at first there was no hum, and then it developed after a while?
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    Tube amps that will run at 2 ohms

    Agreed; I get that too.
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    Were There Any Safety Requirements When The Scott 299D Was Made?

    Not wanting to be too pedantic, but that 5 watt heating you mentioned would only be true for a non-reactive load, like a 2.7K resistor. For an ideal capacitor, the current is 90 degrees out of phase with the voltage, and the power dissipation would be zero. For a practical capacitor there will...
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    Tube amp topologies

    I think the reasons for excluding OTL are slightly overstated here. I have made a couple of OTL amplifiers that use just two output tubes per channel, and they achieve 25W per channel. The tubes are powerful, it is true (Russian 6C33C), but fairly easily available. There is nothing particularly...
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    David Berning's new fleawatt OTL

    It is rather misleading for this to be called "OTL" since it has a transformer (albeit running at RF frequencies) in the output stage. Also, it is a hybrid of tubes and transistors, with the current that flows through the speakers being switched by transistors. It is without doubt a very...
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    How to safely discharge capacitors

    I wasn't quite clear what Unabubba's grounding set-up was. Presumably he is using his ground from the 5ft stake as an addition to the default grounding from the third prong of the mains socket, not as an alternative to the standard mains ground. In other words, I suppose he is effectively...
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