Left Channel Whining

[pts211]

Hey everyone,

For the most part, I have been enjoying my Crack the last couple weeks. Unfortunately, recently it has been a nuisance with a constant whine in the left channel. The whine is a constant volume regardless of the pot value and seems to . I can also hear the sound coming from the 6080 tube.
Is this indicative of a bad tube? If not, I'm hoping someone can help me figure out what else this might be.
I've included a link to a recording of what I hear coming out of my headphones left channel for reference. Though it isn't the highest quality recording hopefully it can help.

http://clyp.it/10fjyzaz

It seems like many of the recent posts are related to a noise of some kind or another, I wish I didn't have a reason to contribute even more to it!

Thanks,
Paul

 

[Doc B]

The level is really low. It sounds like it could be outside interference, or it could be a tube in oscillation. Try turning off other gear around the amp and see if it changes or goes away. Also try removing the tubes and reinserting them to clean the pin contacts.

 

[pts211]

Doc,

The recording didn't do the noise justice in some regards. I was able to hear the noise coming through with music playing. I did what you've suggested and it seems that reinserting the tubes have helped. I haven't had that noise come back tonight at least. With any luck that did the trick!

The noise was pretty consistent, is it common for tubes to get stuck in oscillation? Also, is it normal for tubes to make small noises here and there even once warmed up? The crack is my first tube amp and I clearly have a lot to learn still!

Thanks for your help,
Paul

 

[Grainger49]

I didn't find any mention of shorting or shorting plugs in this thread.  So...

If you don't have any jumpers, wires with alligator clips on each end, go to Radio Shack and buy a pack.

Put a jumper on each of the RCA input jacks bridging the red (right channel) wire to the black wire, and bridging the white wire (left channel) to the black wire.  This eliminates your source as the origin of the noise. 

This does not eliminate outside radiated noise as Dan has suggested in reply #1 above.  So you need to do that first.

A good tube doesn't make noise after it has been properly formed and has been on for a minute.  You might need to burn in the tube for 100 hours, 4 days turned on.  I first got tubes in my system in the mid 70s and the noises you describe are not normal.  Matter of fact I have never had this problem.

 

[Doc B]

About 20 years ago I acquired a rather rare and interesting antique radio, a Jackson Bell Pandora. (can't find a pic on the web). It had a howl that I just couldn't seem to get rid of. I finally found one of the old two piece shields that fit around shoulder shaped tubes and put it around the 1st audio stage tube. That seemed to work for a while, but the howl came back. Eventually I figured out that it was simply a bit of corrosion on the tube's grid pin that was causing the oscillation. A good cleaning of the pins solved the problem and I was able to remove the shield and keep the radio completely original.

And yes, tubes can make a little noise now and then.

 

[pts211]

Sorry I'm just now getting back here, its been a crazy week!

Grainger - I hadn't tried taking the inputs to ground but had disconnected and still heard it before. Should something else come up I'll keep that in mind.

Doc - I'm surprised that a little corrosion can create that kind of effect. I will certainly remember that going forward! I haven't had much listening time lately but have yet to hear anything like I did since reinserting the tubes a few times.

Thanks again for the help, I appreciate it!

Paul

 

[Grainger49]

An open input is like an antenna.  That is why Dan suggests shorting plugs.