@alexberger The resistor value isn't critical. 50 to 100 Ohms works nicely. As long as both chassis (power supply and amplifier) are tied together and grounded by the power cord, its really not going to matter where that resistor actually is, since it will carry no current under normal circumstances.
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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Hi @lynn_olson , The Hashimoto PT-100F power transformer that I'm going to use for drivers/input B+ and drivers/input filament. But I'm not sure if it has an electrostatic shielding between HV and LV sections. I can see some strips between high and low voltage windings. But as far as I can see they are made from a kind of cardboard. |
If it doesn’t say "electrostatic shield" there’s no copper foil between windings. Medical-grade is even better, with primary and secondary on opposite sides of the core. If you want full isolation, in the absence of these features, you need two transformers, one for HV, and another for LV. The name brand doesn’t change the shielding, or lack of it ... that requires copper foil isolation, which is a definite hassle for the transformer builder. I should mention the heaters for the rectifiers do not need isolation. Only the heaters and filaments for audio tubes need isolation. If DC regulation is chosen, a higher secondary voltage than 6.3 volts is needed, since regulators need to throw away a few volts to operate. I should mention not all regulators are the same; you can do a lot better than generic 3-pin regulators. |
... Actually, sonically the statements and the Blackbirds have similar heritage, but the Blackbirds are much better. The Monolith Magnetics iron is just sublime, plus the power supply is improved in several ways including the addition of the pair of VR tubes. The result is the Blackbird kicks it up a notch from the Statements, which were sort of a final prototype before we just pulled out all the stops and made the cases larger on the Blackbird. I just returned from Utah, where I taught the guys at Spatial the builds of both the amps and preamp. There will be actual units for purchase in January. |
I showed the pix of the Amity (1997) and Karna (2003) amplifiers to emphasize they were developed largely in isolation from the SET community. I found out the hard way that SET practice wasn’t always useful with this approach. Similarly, practice in the traditional push-pull pentode world isn’t always helpful. Don’s build and design experience with the Valhalla and Kootenai has been very useful, showing me what worked, and what didn’t. So there are elements of the Amity, Karna, Valhalla, and Kootenai in the Blackbird. Do they sound like SETs? No, they do not. Do they sound like traditional push-pull pentode amps with feedback? No, they do not. The signal flow and functionality is different. The closest similarity are to some unusual designs of the 1930’s, with the very latest 21st-Century transformers and power supplies. The Blackbird is actually the result of a four-way collaboration ... between Don, myself, the transformer designer, and the power supply designer. |
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