[Elysian]

3 out of 4 of my EML 300Bs have picked up nasty microphonics after about a month of use.
 
1) When warming up, the tubes will make a sound like a single loud bell ring every few minutes
2) If the tube is very gently tapped with the back of a pencil or paintbrush, there is a loud ring that echos through the headphones
3) The tubes now pick up even the slightest bit of vibration.  If no music is playing, I can hear the vibrations from typing on a keyboard
 
I read on guitar forums that high temperature resistant o-rings at the auto store are a cost-effective solution that work just as well as Herbie's and other audiophile products.
 
Has anyone else had microphonic issues with notoriously micrphonic tubes like the 300Bs?  I'm unsure whether it's better just to try to get the tubes replaced or to assume that 300Bs are, by nature, very microphonic, and consequently need mandatory tube dampeners.  If the dampers will only get rid of part of the microphonics, then I should probably get them replaced.

 

[hodgjy]

Tube dampeners can help, but in my experience, once a tube is microphonic, there is no cure.  There are only degrees of being microphonic.  They may help.  Try Herbie's Labs for fairly reasonable dampers.

 

[El_Doug]

Here's an idea:  stop tapping the tube with an eraser  

 

[KingStyles]

The pinging noise when a tube is warming up is normal. It is just the sound of the metal expanding as it warms up. Also, never tap tubes. Most tubes will make noise when they are tap with something. Neither one of these is a bad thing.

The typing of the keyboard could mean they are overally microphonic. First. how close is the keyboard to the amp? Some type of isolastion platform to help soak up vibration along with tube dampeners could help with the problem. Nothing fancy needed. Maybe some racquet balls cut in half under your amp for testing to see if it helps.

 

[Elysian]

I guess I'll ask Herbie and see what his suggestion is.  My tube dealer isn't available at this time so I was wondering if dampeners would be a reliable fix in the meantime.
 
Yeah, I only tapped the tube very gently after looking at a number of tube sites that recommend doing that to check for an overly microphonic tube, after I realized that even tapping the chassis is transmitting some of the vibrations.  The preamp is already equipped with integrated aluminum isolation feet (the feet fit into discs; supposedly the design is based off of Japanese earthquake protection tech), so it's already somewhat isolated.
 
It used to be fine, and only got really annoying in the last week or two.  The keyboard's about two feet from the tubes.  I figured that the ringing sound for the first 15 minutes was just the material heating up, but the vibration transmission is new.
 
It sounds like you guys are right about some of the tubes going microphonic.  I read that the EML and KRs can get noticeably microphonic, which is a bit frustrating.
 
Maybe I can isolate my keyboard
 
The preamp hasn't sounded as good as it used to (things sound a little less detailed and more woolly), and I wonder if that's attributable to the power tubes going microphonic.

 

[Elysian]

Well, in case anyone is curious about the end of my ordeal, I managed to solve the issue.  I got rid of the spike feet underneath the preamp, replaced them with a quad of Herbie's tenderfeet, and put Herbie's tube dampeners on all of my preamp tubes.  Vibrations are all completely gone, and the sound actually got dramatically better.  Soundstage opened up quite a bit, everything is much tighter, and percussion is much more 3D and resonant.  I honestly can't believe how much of a difference this upgrade made.  I've spent way more money for much smaller increases.
 
I really, really recommend trying out Herbie's tenderfeet and tube dampeners for anyone using tube gear.  I'm still pretty amazed at what a difference these things made.
 
I also took the advice of some people and used isolating feet under my DAC and USB/SPDIF converter.  It did help a bit, but the improvements were more nuanced.  For the price, though, it's a no brainer.

 

[KingStyles]

Glad you like them. I am using the same thing. Tenderfeet underneath all my equipment and my isolation platforms and herbie tube dampners on all 13 of my tubes. I have never liked spike feet. They seem to do more bad than good.

 

[Elysian]

Yeah, I never realized spikes were so poor at limiting the effect of vibrations.  I'll be getting two quads of tenderfeet for my BHSE without question.  I'll also be dampening all my tubes going forward.  I thought it was just audiophile smoke and mirrors, but the effect of these tweaks were more significant than any NOS tubes I've swapped in.
 
Out of curiosity, did you notice a big difference going from the standard feet to tenderfeet on your BA?