[erniek]

Recently I purchased a Candela tube Pre and when I touch my cd player to open or close the drive I hear kind of a ringing sound that I have not heard before.
It happens even if I just tap the CD player case. Is there something about tubes that can cause this?

[JackD]

Sounds like you have a microphonic tube somewhere.  If the Candela is your only tube piece then one of the 12AU7's needs replacing.  They can be found for less than $30 a pair.

[SJ David]

Recently I purchased a Candela tube Pre and when I touch my cd player to open or close the drive I hear kind of a ringing sound that I have not heard before.
It happens even if I just tap the CD player case. Is there something about tubes that can cause this?

I agree with JackD. I purchased a new tube amp from another maker last year. About 8 months or so in I heard a ringing just as you describe. I could tap the shelf, the pre amp itself and hear the ring. The manufacturer confirmed a tube was the likely problem and sent out a new pair of tubes. No ringing after replacement (didn't have to replace two tubes but now I have spare). "That is just part of working with tubes" was the response from the company, paraphrased.

[/mp]

12AU7 are a common tube. Readily available from many vendors. Include in your pre-purchase research Roger Modjeski's http://www.ramlabs-musicreference.com/ if you don't already have a preferred vendor. Music Reference has a forum archive on audio circle. In it, Roger claims he buys tubes in bulk, tests & throws out substandard tubes. Ram Labs is the tube brand; Music Reference is the audio equipment brand.

Good luck & enjoy,

[JoshK]

This is a very easy diagnosis.   Its likely microphony like mentioned.   Does the top of the case come off so you can gain access to the tubes while it is on?  If so (carefully, don't touch anything else) remove the top, turn it on and let it warm up.  Then with your fingertip or a pencil tap each tube one at a time.   This should help you pinpoint which tube it is.    Of course you can replace both, but I'd personally want to confirm the problem.

Is your wall voltage >120v?   I don't think this is your cause, but its quite possibly a contributing factor.   Tube heaters are meant to be heated by a specified voltage plus or minus a range.   This range can be narrow, if wall voltage fluctuates, so does your heater voltage.  Often too high a filament voltage makes tubes microphonic.  Us DHT tube amp builders use this trick to quiet down microphonic DHT tubes (often) by purposefully under volting the heaters by half a volt or so (within the spec limit).   

[erniek]

The Candela is new, only a couple of weeks old.

[erniek]

One other question concerning this is does it affect the sound in any way?

[firedog]

One other question concerning this is does it affect the sound in any way?

It sure can

[erniek]

what would be some of the characteristics of how a microphonic tube can affect the sound from my preamp?

[JackD]

If you bought this new from Klaus, contact him or Alex about the tubes.  If you bought it used you will just have to get different tubes.  Should not generally affect the sound unless you are handling the Candela or connected equipment. 

[klaus@odyssey]

Hey Ernie,

call me...probably got banged in transit,  as this can easily happen with tubes....not a biggie,  will get you a new one,

Klaus