![]() Unless there is some special low noise/ signal level issue, like say a phono or mic input, the simplicity and already ready already of using the AC out of your power transformer is the way to go.Pull-Through System (negative pressure or vacuum) ![]() Most people here seem to be looking to build a hifi amp for music, and in that case for line level in, speaker out, DC is just not required at all for top notch performance. I am completely against doing something that doesn't address a problem or an issue. so what is there to debate at this point? I mean how do you say, you cannot measure it's better, but it's better? All that knowing that DC causes the heater filaments to fail earlier too. so where's the catch? I've built headphone amps, pre amps, power amps, guitar amps and all of them AC heater powered, and the guitar amps on 10 still dont have excessive or loud hum. added cost, complexity and possibly worse results. I also think that pretty much everyone above said, "you can make a good low noise AC heater powered amp but." That's when I go, what but? For the same reason that a manufacturer won't do it, you shouldn't do it. Starve your heaters and you will destroy the sound and output of your amp. As for being measurably better, it is DEFINITELY measurable WORSE if the voltage drops as a result of converting to DC, which as I said prior happens all the time when people think they need DC because of some internet forum post and they rectify the 6.3 VAC out of their power tranny. transformers are ready to go for AC heater supply. However, this would not be an issue with indirectly heated tubes. The electrons would prefer one end more than the other. But I don't see how polarity or AC vs DC would make a difference with these hot spots.Īre you talking about DHTs only? I could see maybe some emissive coating might get worn with DC due to the fact that one part of the cathode always being at a different potential than the other half. If the resistance along this wire is not completely uniform(it isn't), then some parts will be slightly hotter than others. It's sole purpose is to get hot and radiate that heat to the cathode, so that the cathode can emit electrons. The filament(in an indirectly heated tube) is a wire. I'm not saying that you can't make a great amp with AC heaters, but it is in a tube amp manufacturer's best interests to create a little fear, uncertainty, and doubt regarding DC. One that costs less and is easier to manufacture and brings in a greater profit if they can market it well. My concern with trusting a tube amp manufacturer is that I suspect that they may have been trying to sell an amp that uses an AC heater supply. In my opinions it is better to tear some hair out now (I am young and have lots of hair) figuring out, in the 'learning by doing' way, how to work with AC, than to always have to recur to the hardest and more expensive DC way in future projects.ĭHT tubes are a different matter, which I leave for people as Kevin, who is using CCS to feed 300B's! In my recent projects I am trying to use AC. The common 6.3V AC from the power tranny can only be used for 6.3VDC if one uses a low drop out regulator.to obtain the 6.3VDC from a normal regulator (317, 350) one needs about 9VAC, which in most cases means a separate or custom wound transformer. with a regulator comes the need for heat dissipation: is the chassis enough, or should one add a heatsink? without a regulator, higher order harmonics are added, so a regulator is a good thing, ![]() more components: bypassed diodes, elco's, (Possibly right, but I don't expect everyone to be willing to learn perfect AC dressing for a small number of projects they will be doing throughout life)ĭC heaters require quite some additional efforts in the PS. Following that line of though, I remember a diyaudio member once stating that DC is for people not skilled enough to use AC. I think that it is meant to avoid disappointed people that could not get it 'humfree' with AC. So, why DC? Although Morgan Jones speaks about an AC fed RIAA stage, he presents a schematic for the regulation of the heater supplies for the RIAA stages. And the RIAA stage is the most senstivive to pickup hum. In Valve Amplifiers Morgan Jones states that with good practice even a RIAA stage can be made quiet using AC heaters.
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