Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Smash => Topic started by: Frihed89 on October 29, 2014, 05:33:06 AM
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I mentioned this preamp to an acquaintance who is an avid fan of 26 preamps and uses the 4P1L. He writes to me: "The tube is microphonic, so needs special treatment to dampen the potential for vibration (like a massive chassis or some rubber-ish decoupling) and starving the filaments helps too."
What does "starve the filaments" mean exactly: how and by how much? Has anyone tried this on the 4P1L? If so, did it help.
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I've been playing with these tubes recently, there is an opinion (mainly on DIYAudio) that running the filament voltage slightly on the low side helps reduce micrphonics/ringing. Personally i don't see the issue, i fed them 4.2volts and they weren't in the slightest bit microphonic at all. Maybe i just got a lucky set.
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If you have severe microphony, then adding weight and damping will help. I haven't experienced that starving the filaments reduces microphony, at least not until the tube is no longer emitting as strongly as it should be.