[RESOLVED] A couple questions, or This is What It Sounds Like When Tubes Die

[WK3K]

Hey all,

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[*]I'm getting a mechanical sounding sound from the amp (not the speakers) when I power on the amp, sort of like what you'd hear when you flick a spring — that boing-oing-oing sort of sound. Should this concern me or is this "normal". 
[*] The other night, after listening for 5-6 hours, it started to sound like my highs were topping out and getting scratchy/flat. I chalked this up to playing from a streaming source or maybe just being tired. When I turned the amp off, I turned the volume all the way down and then hit the power. I noticed that the 12AT7 on one side got real bright for a moment when I turned the volume down. Today when I turned the amp on, I had no sound on that side. I wondered if something was up with that tube, so I switched the 12AT7's and now everything is working sounding/fine. Thoughts?
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I'm feeling a little paranoid after my initial build issues. In general it has worked and sounded like a dream, except for the temporary missing channel this morning.

 

[Paul Birkeland]

It sure sounds like you may have a loose connection in the amp.  Having a channel drop, then come back when you swap tubes is consistent with a loose connection that's just touching and conducting well enough to work most of the time.

 

[Jamier]

Witold,

  Have you installed the SR mod? If not, it could be a tube going bad as only half of the 12AT7 is functioning W/o the SR upgrade. With the SR in place, half of tube is involved in the SR circuit, so if you don’t Have the SR in yet, switching tubes put the “good” half of that tube in play, correcting the problem, for the moment. You will need tubes functioning properly on both sides when you install the SR upgrade, an upgrade that most SII owners highly recommend. I think this statement is correct. If not PJ will correct me.

Jamie

 

[WK3K]

Thanks for the input. I do NOT have the SR. I switched tubes again and get the same result. When the “bad” tube is on the right channel there’s no sound and the glow is a different/brighter color. It also doesn’t feel warm like the other tube. Again, the light gets particularly brighter on that side when I turn the volume down and I here a mechanical twang when I turn on the amp with the tube on that side. Picture shows the “bad” tube on the right 

When the “bad” tube is on the left channel everything sounds normal and the glow looks more or less the same. The two 12AT7’s I received look very different, so maybe one was on the way out?

PB, what do you think about this theory?

 

[Jamier]

Witold,

    I hope I didn’t confuse the situation, but it is possible that you have a 12AT7 that is going bad on one side. As PB said, check your connections carefully, but it is possible that 1/2 of that tube is problematic and may be the source of your problem. Do you have any other 12AT7s to substitute? When you trade the 12AT7s you are using the side of the tube that was inactive when it was on the other side of the amp. That is why I’m suggesting that the problem is, possibly, the half of the tube in question.

Jamie

 

[WK3K]

Nope, not confusing at all. I totally get it. I think especially given that the same behavior is replicated only with that particular tube in the right channel is a good indication that you’re correct. I will recheck all connections tomorrow, of course, but I don’t see it being a loose connection that happens to work with one particular tube and not the other.

Unfortunately I don’t have spare tubes laying about, but this seems like the best explanation.

Is it safe to run the amp with a tube that has failed on one side? It sounds totally normal as long as I have that tube on the side of the amp where the problematic side of the tube isn’t in use.

 

[Jamier]

I think if both sides fail you will have the same thing occur that you experienced before: no sound. However,  if that occurs, I would shut it down ASAP. I think PJ or PB will let you know soon. I would get some B/U tubes though.

Jamie

 

[Paul Joppa]

What Jamie said. One triode uses pins 1, 2, and 3 for one channel; the other channel uses pins 6, 7, and 8 on its 12AT7. This is done so that if one triode fails you can swap tubes and use the other triode. Which you did, and apparently it's working. It's like having a (full-size) spare tire in your car!

The second triode in each 12AT7 is only used with the shunt reg kit.

So now you have music again, and plenty of time to acquire a replacement spare 12AT7.

 

[WK3K]

Thanks PJ.

That's a great little design trick that y'all have incorporated. I'll probably pick up the SR at some point in the future, but want to enjoy the amp stock for a while and already have the DC filament supply to build and install first.

Another thing I love about BH: every time I have a "problem", I'm really getting an opportunity to learn something new.

I've got a couple new tubes on the way. Will be good to have some backups one way or the other.

W

 

[Paul Joppa]

That's a great little design trick that y'all have incorporated. ...

That trick goes back to the Paraglow, ca. 1998 I think. Probably came from John Tucker - possibly Doc B or John "Buddha" Camille.

 

[Jamier]

I really miss full size spare tires.

Jamie

 

[Doc B]

I always found them a little bit cumbersome.

 

[WK3K]

HA!

 

[Thermioniclife]

I wish I could hide my actual spare tires as spare tires like this guy.

 

[denti alligator]

To the thread title: I've had one channel go out on my Stereomour and that was that--it just stopped making sound.

However, recently I switched out the tubes on my Seduction and it was a night and day difference. I had some loud tube rush, which I chalked up to the way things are... even though I've been using this for like 10 years! But you get used to sounds that even are unpleasant--when they creep up on you, you hardly notice. But it was getting pretty loud, so I switched them out and no the amp is almost dead quiet! Plus I seem to have more db going--at least the amp is louder.

So, tubes die different deaths, I guess...