How to deal with microphonic 300B tubes.

I have a used set of Cary CAD-300SE LX-20 mono amps, and I just love them with my Coincident Victory speakers. But I occaisionally get a weird, intense ringing microphonic from them, especially noticable when an FM announcer's voice hits just the right pitch.

I have them just sitting on my tiled floor, no attempts at vibration stands yet. I'm sure this could help a bit, but I am also thinking that tube dampening could be needed.

Any suggestions? Are there appropriate tube dampening strategies for 300B's?


What tubes are you using?
They are tubed with the Kron KR-300B LSX tubes from Czechoslovakia.
Herbie's Tube Dampers wouldbe the first thing I'd try. Call Herbie first to find out which one's would work best with the KR's. I think the KR internal(and external)structure is more heavy duty than TJ's, WB's, may need a special version.

I tried a friends on a few of my tube amps recently and the improvement was easily noticable. Clarity, focus, and silence that I had no idea was missing. As a result, I've ordered a fullset for my ams and preamp.

Do an archive search hear and on Audio Asylum's Tube forum for user opinions.

Herbie's Audio Lab

6Moons review(1/2 down page)
Positive Feedback review
TNT Audio review(1/2 down page)
Enjoy The Music review(1/2 down page)

I had a similar problem with KR 300b XLS's in my Cary 805c's. You may want to try KR 842VHD's. I found the 842's to not have any problems with microphonics in my system. I think they will work with the LX-20 version of your amp, but make sure to check with Cary.

Be aware, though, that the 842's will sound much different. I found them to be smoother and warmer sounding, but with some loss of bass impact and musical weight.

Thank you for your input. The Halo do seem worth trying - - I have used dampeners before, and they always seemed to help. And the Halos are designed to let the tube still convectively cool, which I like.

The ringing I have been hearing is a fair bit more than I've ever encountered from a tube before, and very focused on a frequency. Maybe the Kron tubes are more prone to this, I don't know.

I don't believe that the Cary's can run the 842's. They don't say this in the manual, but they do warn you not to try any other 300B's other than the Krons.

I'll have to try out some of Herbie's magic.

Hi Jeff. Interesting observations regarding the sonic differences between the Kron 300bxl and the Kron 842Hvd in the Cary. I would concurr with your findings exactly. The 842 is certainly warmer, more akin to the warmth of the WE300b however I think the 300bxl is the better fit for the 805. It does wonders for tightening up the rather ripe lower registers of the 805 particularly the midbass area,not to mention the gain in fine micro resolution as well as dynamic range. Interesting though..... these same characteristics are also very evident when used as an output tube in a 300b based set amp.
Hi, Ecclictique.

For the record, I use new production Western Electric 300b's in my Cary 805c's. I didn't recommend them to Jay because I know that standard 300b tubes won't work in the LX-20.

I agree with you that overall, the KR 300bXLS make an excellent match to the 805c's. I honestly, just couldn't get past the microphonics of that particular tube.

I also agree that the 842 has a similar sonic signature to the WE 300b. I went with the WE because the 842 has a very slight hollowness to the midrange that the WE does not.

I have done a lot of experimentation with tubes in the 805c's. My favorite combination in my setup is:

GE 6SL7GT with wire top getter for input
WE 300b for driver
Shuguang 845B for output