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#1
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5K OPT in place of 3K ?
Hello,
I have an opportunity to have SE OPT 5K / 0,4,8 ohms. Big good ones second hand, cheap price. But i want to build 300B SE, usually it is more 3K OPT. Is there a way to use them for a 300b amp. ? Thank's BR, Luc D. |
#2
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5K OPT in place of 3K ?
I don't think it is good using a 5K OPT for 300B SE. I would suggest you
could use it for 45 tube instead. Usually, the frequency response for 5K OPT is not as good as 2.5K one. Johnny egroups.com... Hello, I have an opportunity to have SE OPT 5K / 0,4,8 ohms. Big good ones second hand, cheap price. But i want to build 300B SE, usually it is more 3K OPT. Is there a way to use them for a 300b amp. ? Thank's BR, Luc D. |
#3
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5K OPT in place of 3K ?
Thank you for your answer,
The opt i was considering (second hand) is a good one (good frequency response, high impedance). I have seen a lot of discussions in the archive of RAT on this topic : Usually it is considered as a posible choice to take a 5K, but it decreases the output power. In fact i consider the Je labs 300b design. I was wondering how much output power i will have in that case ? I also think that a 8ohm speaker is in fact more near 6ohm at some frequencies, so maybe it is not to problematic to have a 5K opt ? Br, Luc D. |
#4
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5K OPT in place of 3K ?
wrote:
Hello, I have an opportunity to have SE OPT 5K / 0,4,8 ohms. Big good ones second hand, cheap price. But i want to build 300B SE, usually it is more 3K OPT. Is there a way to use them for a 300b amp. ? Thank's BR, Luc D. Consider your speakers, Luc, and their power requirement. How much power do they really require for the sound pressure level you use? Clearly, if you are interested in 300B, they will work with 7W or less, which is what you get out of a standard sort of 3K OPT 300B amp. Theoretically going from a standard 3K OPT TRX to one with a primary impedance of 6K reduces peak SPL. It is not a big deal. If you are designing so close that 3dB or even 5dB in your available transient reserve becomes important, you should get more sensitive speakers or go to PSE or PP. I use Lundahls on the 5K6 tap all the time and going from 3K3 to 5K6 dropped the output of High Voltage, High Current design from 7W6 to 4W8. My current KISS "Fiultra" is a Medium Voltage, Medium Current (320V operating, 65mA, -65V) design to make it safer for DIYers and to ensure longevity of the tubes; it is further limited by the signal available from the single driver, so that it puts out 3W8. I don't notice the difference. My speakers are Lowther horns, which can be seen during construction and development on my netsite. So what do I gain (except a safe construction and longevity) by giving up half the power? The main answer is silence. What happens is that a different impedance on the plate of the power tube (any tube, actually) turns the transfer curve on the pivot of the quiescent operating point (you are building a Class A amp, by definition, if it is an SE amp, so the Q point is at the standing current drawn constantly at zero signal--there is a chapter on my netsite to show how to use the transfer curves or try the RDH or Crowhurst). The higher impedance pivots the transfer curve anti-clockwise, thereby making it flatter, raising the right hand side further above the turning bottoms of the negative grid bias transfer functions (the diagonal -Eg lines), and removing the end of the positive going signal (the left hand side) further from the possibility of grid current. The result is more linear power transfer, for which in English we say: "Silence!" The theoretical limit of load impedance increase, given infinitely sensitive speakers of course, is set by a horizontal transfer curve, at which point zero current change occurs and no power is transferred. A more realistic theoretical aspiration is a loadline running perfectly perpendicularly through precisely evenly spaced Eg-En-Ia curves (a condition the 300B and very few other power tubes approach at all closely); the limit here is set by how much current maximum dissipation spec allows you to draw. In fact, the highest common load-impedance pivots the loadline (which is the transfer function of that particular OPT impedance with that particular tube and those particular operating parameters) well past the perpendicular-to-transfer-curves to get enough signal swing to get good power without running into the nastiness where the curves fall over at the bottom and without dissipating unconservative amounts of power. Thus, beyond a certain point, which might be about 6-8K depending precise operating parameters, a higher load will again lead to a less linear sound, i.e. more distortion. Today it is widely considered that 5-6K is the ideal compromise. (You may have heard about the notorious flame wars on RAT and elsewhere. The winder and his pals assaulting me were in part inflamed by my early advocacy of higher load impedances on DHT, which undermined their commercial interest since the winder had only old-fashioned low-impedance designs in his catalogue, at that time nothing higher than 3K5.) **** If you're going to the expense of 300B in the first instance, you should already be in a position with your speakers where you do not need to hog the tubes out for maximum power. Frankly, I now consider 2K5 (common 30 and 40 years ago, actually the max to be inferred from the RDH recommendations!) a grotesque mismatch to 300B, a waste of good tubes. Nor is 3K fabulous; for quite a bit less money if you shop carefully you can build a better amp using trioded PP EL34 with film caps everywhere except in the power section. You'll be amazed at the quality of components for such an amp that you can buy straight out of the RS catalogue. Someone wrote to me the other day, after I said good amps cost roughly the same to build whatever the chosen topology, that a careful costing of my T113 Triple Threat (PP trioded EL34), T44bis KISS Populaire (standard three-stage 6SN7-300B, a very silent amp at any power) and T39 KISS Ultrafi (what it says, WE 417A into 300B, a low-power ultra-silent amp), all three of which he has built, reveals that the T113 EL34, which I designed to be built out of the RS catalogue, costs about three-quarters of the price of either of the 300B amps. According to him the price difference isn't in the tubes or the transformers (Plitron/Amplimo for the PP amp and Lundahl for the 300B amps) but because the 300B amps depend on very expensive polyprop caps in the power supply. The best 300B until ten or fifteen years ago used 3K5, a very popular load in Japan and among the Japanese-inspired Americans. It seems to me that today even a really good commercial Japanese 300B amp starts at 4K load (the PSE Miyabe from Triode Supply Japan, known in Australia as the VPD3000, uses a 2K OPT for the parallel tubes). Your top-end DIY audiophile generally starts with 5K, a great many of them like my own fave of the Lundahls on 5K6 if my mailbag is anything to go by, and the niche guys like Lucas Cant's 6K. HTH. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "an unbelievably comprehensive web site" -- Hi-Fi News & Record Review |
#5
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5K OPT in place of 3K ?
Thank you for your very detailled answer, with a lot of references.
I gives me a summary of what i was looking for. So clearly 5K is a good choice. At the moment i don't have the speakers for this amp. I have to think about this also, later. I have seen the flame war between 3K and 5K, the pros and cons. What do you think about running a 300B a bit harder to get 7-8W with a 5K opt ? (8W i think is a lot of power so that i can have more choice when i choose speaker : ie be able to choose 'inexpensive' good second hand speaker). Also 300b tubes are not so expensive now, if they last 2000h it is ok for me. I precise that i usually liten to music at a low level. At the moment i listen to KT88 PP williamson into KEF concerto and i have 10 time too much power (in a big listening room 6m*7m). I plan to use the 300b in my bedroom (3.5m square). Note : i plan to put on the web some photos and a description of the williamson (gec 30w improved) amps i built with the help of a lot of guys here. The first one is finished, the second one is half done. So i listen to mono : and you know what ? in fact good mono is ok for me !!! ;-) I'm very happy with the result (it took me a lot of time to get it right) thank's a lot, BR Luc D. |
#6
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5K OPT in place of 3K ?
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