4P1L:"Starve the filaments"?

[Frihed89]

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.

 

[mcandmar]

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.

 

[Paul Birkeland]

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.