@atmasphere Hi.. you are only running 3 6sn7 tubes. Input tube and then a long tailed pair driver on each side using a single 6sn7....
300b lovers
I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations. I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is. Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.
Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence. They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music. They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding. Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a unique circuitry to mate with his 300b monos via XLR connections. Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it.
I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system. 300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm. Of course, 300b amps favor efficient speakers so carefully component matching is paramount.
Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public. Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC. I will be there to hear what I expect to be an outstanding sonic presentation.
To allay any questions about the cost of Don's 300b mono, I do not have an answer.
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@alexberger Mostly because of the voltage swing. RC coupled circuits are a bit inefficient if you also want current to deal with that input capacitance (which admittedly isn't all that much). That is why transformer coupling or better yet, direct coupling, does the job better.
@donsachs So 'only' 0.9 amps more... I think I've seen too many power transformer failures in my life, although that's mostly been due to bad filter caps. I treat old power transformers carefully- to avoid Bad Things happening. |
@atmasphere the ST70 power transformer spec was allegedly 2 x 6.3 V windings @5A each. Pair of el34 is 3 A, even a pair of 6sn7 is only 1.2A, so that should be only 4.2A. Should be safe |
What makes the 45 or 300B "hard to drive" is that it is good practice to have the majority of amplifier distortion in the final power device, not the driver. In other words, the driver should be cleaner than the 45 or 300B ... which are the lowest distortion tubes ever made. In a feedback amplifier, the source of the distortion doesn’t matter much ... the feedback sweeps it all away. Which is why the substitution of the higher-distortion 12AU7 for the lower-distortion 6SN7 in the mid-Fifties didn’t matter much, since feedback was in universal use by then, and it didn’t show on the low-resolution distortion analyzers of the day. To be honest, zero-feedback amp design is kind of a cult audiophile thing. For that matter, any kind of tube amp is a cult audiophile thing. If distortion numbers come first, THX or Class D are the answer, end of story. Don’t mess with tube amps, just buy the solution off the shelf. It’s an esthetic decision to build zero-feedback amps, whether bipolar transistor, MOSFET, or vacuum tube. I think it is good practice to design low-distortion zero-feedback driver sections, but I have seen (but not heard) all-transistor amps, with lots of feedback, used as 300B driver sections. Which begs the question, why use a 300B at all, if it’s just an expensive distortion generator? Returnng a little more seriously to the original question, there are a lot of SET amplifiers with marginal driver sections. I’d go out on a limb and say the majority of 300B amps on the market sound mostly like overstressed driver sections, not like a 300B. That’s why some of this discussion might sound like we are at cross-purposes. If state-of-the-art SINAD numbers are your goal, please look elsewhere. Forget all tube amps, whether pentode, triode, or hybrid amps. If you want a taste of "tube flavor", get a preamp with a 12AU7 in it. I own a charming little Xduoo TA-10R, which is a AKM 4493 DAC, a 12AU7 gain stage, and a simple two-transistor Class A output stage. 2 watts per channel, sounds great, and all for $320 from Apos Audio. Lots of power to drive planar headphones, and a fun alternative to the usual Topping or SMSL. Designers of zero-feedback 45 or 300B amps have different goals, which are also different from designing re-creations of Golden Age PP pentode amps. A lot of it comes down to esthetics and design philosophy. |
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