High pitched whine in right channel (Resolved)

[malloy]

Hi,

I just finished my Crack build. Sounds terrific. But I've come to notice a very high pitched whine in the right channel.

 I switched interconnects, still the same.  It is barely noticeable (only during quiet passages do I hear it) and does not get louder even if I turn up the volume.  The left channel is dead silent. 

Is this normal? I am using the Crack in a computer setup.

Thanks for your input!

[Doc B.]

Try unplugging and replugging the tubes two or three times to burnish the pins a bit. That oscillation is often caused by oxidized tube pins.

[malloy]

Thanks, Doc. Will try this tonight after work and report back.

Is it safe to clean and treat the pins with Deoxit?

[Doc B.]

Yes, Deoxit is fine. My favorite pin cleaning trick is to cut a Q-Tip in half and chuck it up in a Dremel tool to use as a pin buffer with some metal polish like Noxon. Then treat the pins with your favorite contact treatment.

Plan B - Check to make sure the whine  is not coming from outside of the amp, like from a dimmer switch, computer, etc.

Plan C- It may be a flaky contact from a cold solder joint somewhere. You could try reflowing the solder joints on the channel that is whining.

[malloy]

Cleaned the pins on both tubes with deoxit. Significant improvement. The noise is nearly inaudible, but it is still there. I'll try cleaning some more. 

Upon closer inspection, the pins of the 12AU7 seem duller. Maybe it is more oxidized and should get more attention? 

I've also eliminated the possibility that it is the computer - I turned everything off except the amp and still hear the sound.

Another question, Doc. If I reflow the solder on the channel as you advised. Which is which and where is it? I'm assuming those are the wires that go to the TRS jack? Sorry - total beginner to this DIY and troubleshooting, as this is my first build.

Thanks!

[malloy]

Cleaned the pins again with metal polish and Dremel then retreated with Deoxit. 

I also resoldered the headphone jack wires. No luck.

Can it be the tube going bad? What are the chances of the tube settling in (and quieting down) after x number of hours?

[fullheadofnothing]

The circuit for a channel is more than just the output jack. It starts at the RCA jack, goes to the pot, then to the first tube, then to the second tube. About half the pins on each tube, plus associated components (resistors, capacitors, diodes) are all relevant here. Checking all solder connections will take just about as long as trying to single out things only connected to one channel.

Yes tubes can quiet down as they get used. A tube that is still making noise around the 50-100hour mark will probably not get quieter, but of course that test is only valid if you KNOW the tube is the problem (i.e. you have a known flawless amp). The test to see if the noise is coming from a tube is to get another tube. Crack tubes are cheap and easy to find...

[malloy]

Hmmm. I retouched all the solder joints and resoldered some on the tube pins that I  was not satisfied with. Still no luck.  I'll have to try the poke-with-the- chopstick method next.

Another question - when I put my ear right next to the power transformer should there be an audible hum/buzzing sound?

[malloy]

An update:

I just received new tubes to test - a NOS-6AS7G from tubedpeot.  It seems like the right channel has quieted down completely but this new tube is even noisier on the left channel and microphonic! I guess I can mark the topic as resolved as the cause was not wiring but the tube itself.

My question now is - is it possible to return a microphonic NOS tube?

[borism]

I would contact tube depot. They have a good reputation and most likely will exchange the tube.
Good luck!

[malloy]

Thanks! I'm just glad to know that the reason for the noise wasn't anything I missed in the build. I hate chasing down gremlins. My wife thinks I was paranoid and imagining things!

[Paul Birkeland]

I microphonic tube isn't the end of the world, just don't thump on it with your fingers.

-PB

[malloy]

Yes, the microphonics quiet down a bit after being on for a while, but there is also a much louder hum on the left channel this time, on top of the ringing.  There also is something physically rattling inside the tube. The stock tube it replaced was very quiet in comparison with the exception of a faint hum on the right channel.