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bob p

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bob p last won the day on January 27 2014

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About bob p

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    TO-92 Transistor

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  1. Let me guess -- setting up the stereo was one of the first jobs that you tackled when you moved in, right???
  2. Yes, tubes sound different. But when similar tubes sound markedly different in the same amp, the first thing that I look for is a setup problem. Was that a cathode biased PA amp or a fixed biased PA amp? As I'm sure you know, all tubes have different operating characteristics, and properly biasing them is very important. Properly biasing is fairly easy with "fixed" bias designs that offer an adjustable bias setting. Properly biasing is a bit more difficult with "cathode" biased designs. To properly balance those circuits you're forced to select tubes that will dissipate an appropriate amount of power at the current level that's provided by the cathode bias resistor. This kind of bias paradigm is particularly sensititive to tubes that lie outside of a narrow performance envelope, which means that some tubes that don't have the right characteristics will never sound good in the amp. Its essential to select tubes whose operating conditions (cathode current and plate + screen dissipation) fall within an optimal range of power for the tube while falling within a narrow range of current defined by the cathode bias resistor, or you have to select a cathode bias resistor that will result in the proper amount of power dissipation for the tubes, confining your dissipation and current values to a relatively narrow range. These requirements mean that there are a large number of tubes that will never function properly (sound good) in the circuit. Most people who get into "tube rolling" fail to address these issues. Most of them wouldn't consider calculating the desired value for a new cathode resistor, unsoldering the existing resistor, and replacing it with a new value when swapping tubes. Users get tripped-up by making the assumption that cathode bias is "automatic" bias. It is not. They tend to imagine tubes as "plug and play" devices when they are not. If proper biasing and power dissipation characteristics are not met, then the tubes will not operate in the appropriate range on their characteristics within the circuit. This causes the tubes to end up sounding more different than they would with a proper setup. The problem with "tube rolling" is that to get optimal results you need to tweak the circuit with the new gain device in-situ. If that kind of tweaking doesn't get done, then the "tube rolling" experiments will produce data points that are impossible to reproduce, and subject the outcome to chance occurrences based on sample variation rather than controlled experiments with precisely defined electrical characteristics. Of course, "tube rolling" is still fun, so there's good reason to do it. It has to be understood though, that its a totally non-scientific approach that solves the problem by blind trial and error. The obvious analogy is the one of the blind pig that finds an acorn. IMNSHO most "tube rolling" experiments by audiophiles lead to meaningless observations that can't be reproduced because so few people actually understand how the circuits operate and make a successful attempt to control the active variables in the experiment. For most audiophiles, it's blind plug and play.
  3. pretty sure you can download rc-30 from pete millett's site. if you want a hard copy, CE Distribution sell them pretty cheap. edit: also available at amazon
  4. Thanks for the offers to help guys. but as Kevin mentioned, he's already got the stuff boxed up to go to two different directions, so there's no point in trying to scramble to re-shuffle the order. I appreciate everyone's flexibility and willingness to help. Actually, depending on how long each person is supposed to keep the unit, it might be a problem for me to get it sooner rather than later, given my current total lack of understanding of the interface. I'd like to start trying to get my ducks in a row now, so that I don't hold up progress if my configuration isn't plug and play. so I have two questions for you guys: 1. Is there some documentation for this device that I could look at, and get a jump on the configuration issues? 2. How long is the demo period supposed to be? Thanks!
  5. Maybe I'm just a total dolt, but I interpret that to mean that the DAC will transparently adapt to the data stream that you're sending it in a plug and play fashion. The problem is that on my PC, the default configuration is to stream the data to the soundcard, not to a USB port. Some change has to be made to redirect the data stream to the USB port, or the DAC's ability to automatically respond to the data never enters the equation. How can the DAC automatically respond to the data if the data never gets sent to the USB port in the first place??? At least that's the most sense that I can make out of it... Maybe I'm just a big dummy.
  6. Man, I still don't get it... Presto? What OS are you using, Windows? Is there another driver that's being used in lieu of the soundcard driver? There's got to be a switch that gets flipped somewhere in the software that changes the default output device, no? Just wondering -- has anyone used these things with linux?
  7. If it makes sense to keep the shipping distances short to minimize risk in transit, dog, harry and i are all in the same state. Bill is way out west. Just wondering if there's any point in planning shipping by locations. again, my intent isn't to bump anyone, but it doesn't make sense to spend more money on shipping than you don't have to. it might make sense for kve to deal with shipping one package instead of two. just a thought -- its not a big deal if a change doesn't fit into anyones schedule. I can always wait. when it comes to the USB input, I've got a question for you guys -- when you're playing FLAC files on your PC, how do you get the digital files from the hard disk out to the USB port? I imagine that there's got to be some sort of player/client that can be configured to route the files to the USB driver port rather than to the PC soundcard. just wondering how you guys are doing it. I've never noticed external USB DAC as an option on any of the software clients.
  8. another possibility -- that "scorched" area in the top right corner may just be overheated rosin core flux. some solders have copious amounts of flux in them, and that stuff turns to a nasty brown gunk when you overheat it. the easiest way to tell is to get a flux cleaning felt tipped pen and scrub the "burned" spot. if it cleans up, its nothing but leftover flux that wasn't cleaned off of the board. along the bottom you can tell that a different solder was used. its flux hasn't been removed, and its more of a burnt sienna color (PI) than a dark brown. the joints look cold. if you want to know if the circuit is authentic, get the schematic and trace the components. if you want to know if those two pads that bill mentioned are bridged, get out your ohmmeter.
  9. Rod, do you have an updated version of the rotation schedule? I'd like to know where I fit in. kve77 has some gear he's going to be shipping to me in the not too distant future, and if there's nobody in line after him, or if somebody would be interested in trading places with me, I was wondering if it might be possible to kill two birds with one stone when it comes to shipping. I don't want to cut the line, but it might make sense to ship two pieces of lightweight gear together if the solution is workable. thanks.
  10. Might depend on the market it was manufactured for. Where was it originally sold?
  11. congrats on the new gear. the stiff nature of the volume pot suggests that it hasn't been abused with deoxit. overzealous use of chemical sprays removes some of the goop that gives the pots their solid feel. i try to locate my amps on the top of the stack, rather than on the bottom , so they don't send heat up onto your other components. my personal opinion is that a preamp, tuner or a CD player should never be placed above an amp.
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