300B Tube hum?

[oltmb]

Hi,

I finished my BeePre Limited Edition last week. I added several sound damping extras like Dynamat on the inside and 4TUBE absorber feet. I also placed the preamp on a wall mounted rack to reduce any vibration from external sources. I added a Rothwell balanced 10dB attenuator before feeding the signal into my Hegel Power Amp.The sound is great!

However there is still a continuous audible hum in the left channel. I found out that exchanging the 300B tubes moved the hum from the left to the right channel.

Can this be a tube problem and not something in the preamp itself? How can I correct it?

 

[ZenAudio]

Sounds like a tube problem.  If you are using new tubes, the problem might go away with time as the tube breaks in.

 

[oltmb]

Ok. I will wait for a few days and see if it improves. Forgot to mention that I am using High Density Silicone Tube Vibration Dampers from Levytubes.

 

[oltmb]

I did not want to wait as after several hours the hum stayed and it was very annoying. I went to the local tube store (www.tubeprofi.com) and purchased a pair of JJ 300B tubes. That immediately improved the level of microphonics and there was no hum. The JJ's have internal silicone damping and it works well. I don't need to use the external damper rings.

I don't like that one of the EH 300B tubes that was delivered with the kit was not working 100%. I guess there is no warranty.

There is just a little bit of 100 Hz hum, but only if I put my ear next to the loudspeaker. For the rest everything is fine.

 

[Doc B]

I don't like that one of the EH 300B tubes that was delivered with the kit was not working 100%. I guess there is no warranty.

I don't know why you are assuming this. All you need to do is contact us about returning the tube for a replacement. Email Eileen at queen@bottlehead.com and she will help you with the return.