2. amps-preamps
  3. 1131597962

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?

Thanks,

Jay
jbrrp1

Showing 3 responses by jeffreyds

jeffreyds
115 posts
 
What tubes are you using?
jeffreyds
115 posts
 
Jay,

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.

Jeff
jeffreyds
115 posts
 
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

Jeff
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