Left Channel Buzz

[kiwipie]

Greetings.

I have just completed constructing a Crack OTL (no speedball yet) for my HD600s and my music has never souded better.

However I've noticed a quiet buzz comming from the left channel. At first I thought it was a bad joint but i've also noticed that I get microphoncs in the left channel only when I tap the chassis, this leads me to belive it may be a bad tube.

Do you think it's worth trying a new power tube before looking for the problem elsewere?

Also if I was to replace the tube what is a good value for money replacement (I intend to install the speedball when I get the money)?

[i luvmusic 2]

 I used RCA,SYLVANIA and CHATHAM/TUNG-SOL 6AS7G's $10-20 per tubes,6080 $6 to $10 per tube and RCA,SYLVANIA,GE 5963 $6 to $15 per tubes.

[Paul Birkeland]

It sure does cost a lot less to touch up all your solder joints before replacing tubes.

-PB

[kiwipie]

Since it's only the left channel effected what joints would you suggest touching up?

[Paul Birkeland]

I would take your needle nose pliers and just start gently tugging on things.  If anything moves within its solder joint, it needs to be reheated and reflowed.

-PB

[kiwipie]

I've just tried that and nothing moved a millimeter.

Also I noticed something lose in the big tube. I can't see it but I can here it if I tip the tube back and forth.

[Paul Birkeland]

There's often debris inside the tube from manufacturing, which shouldn't present a problem.

If you can see metal bits rolling around in the tube, that can be a problem.  Often times, however, it's just a little bit of leftover glass stuck in the base.

[kiwipie]

So what do you suggest I try now?

[fullheadofnothing]

Have you resoldered your joints yet?

[Doc B.]

Reheating joints is a good idea. Is the hum constant, or does it go up and down with the volume control? If it is constant and reaheating the joints doesn't solve it, you might let the tube run for a few days and see if the hum reduces. If not, send the tube back and well send a new one out to you.

[kiwipie]

The buzz is unaffected by the volume control, and re heating the joints has done nothing to solve the issue. I will try leaving the amp running while I am home over the next few days and see if it helps.

EDIT: I've also just noticed that the microphonics are occuring in the small tube so maybe thats the tube the buzz is comming from.

[Doc B.]

Yes it could be either tube. It's not very often that a 12AU7 is microphonic, but it does happen. And that could correlate with buzzing sounds. We are happy to exchange the tube for you.

[kiwipie]

Just an update.

I went ahead and replaced the 6080 and now the buzzing is gone. The 12AU7 is still microphonic but it isnt affecting my music.

Thanks everone for your help and suggestions.