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November 30, 2020, 01:07:32 PM

Author Topic: 4P1L:"Starve the filaments"?  (Read 1595 times)

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Offline Frihed89

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4P1L:"Starve the filaments"?
« on: October 29, 2014, 05:33:06 AM »
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.

Offline mcandmar

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Re: 4P1L:"Starve the filaments"?
« Reply #1 on: October 29, 2014, 06:51:54 AM »
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.
M.McCandless

Offline Paul Birkeland

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Re: 4P1L:"Starve the filaments"?
« Reply #2 on: October 29, 2014, 07:36:19 AM »
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. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man