[replytoken]

One of the 12AZ7's that I received as part of my birthday present sent a loud pop through my amp and speakers last night when I powered up the amp. This was followed by much snowy noise coming through one of the channels. I shut everything off, replaced the 12AX7 to see if it was the culprit (rather than the 12BH7A or the 12B4A's), and things seemed fine. The tube is a NOS Sylvania 12AX7/7025. I am trying to understand what exactly happened; how common this is for NOS signal tubes like the 12AX7; and, if the tube is still good. I have only had one other tube have this happen, a NOS GE 5751 (70's vintage), but I do not remember any popping sound with that tube. The amp is a Mapletree Audio EAR++ III. Any help would be greatly appreciated. I can accept a bad NOS tube every now and then, but I do not want my amp chewing up all of the tubes that I received as gifts. If I wanted that, I would get a puppy!

 

[sacd lover]

Quote:

Originally Posted by replytoken One of the 12AZ7's that I received as part of my birthday present sent a loud pop through my amp and speakers last night when I powered up the amp. This was followed by much snowy noise coming through one of the channels. I shut everything off, replaced the 12AX7 to see if it was the culprit (rather than the 12BH7A or the 12B4A's), and things seemed fine. The tube is a NOS Sylvania 12AX7/7025. I am trying to understand what exactly happened; how common this is for NOS signal tubes like the 12AX7; and, if the tube is still good. I have only had one other tube have this happen, a NOS GE 5751 (70's vintage), but I do not remember any popping sound with that tube. The amp is a Mapletree Audio EAR++ III. Any help would be greatly appreciated. I can accept a bad NOS tube every now and then, but I do not want my amp chewing up all of the tubes that I received as gifts. If I wanted that, I would get a puppy!

The tube may not have been seated properly. But I doubt that. The problem sounds like the tube arched because it has a short. You can try the tube again but if I heard the pop again I would remove the tube permanently. A tube with a dead short can damage your amp so be careful.

 

[mattigol]

Don't mean to thread-jack, but I have a 6SN7 tube (actually two) that display a weird on-and-off buzzing sound occasionally, on top of a ever so slight, but permanent static noise on on channel only. The buzzing really reminds me of an insect flying buy. Logic tells me the amp or tube seating should be at fault (with two tubes displaying the exact same behaviour). However, a third tube from a different manufacturer doesn't show any of this.

I have already cleaned the tube socket.

 

[replytoken]

Quote:

Originally Posted by sacd lover The tube may not have been seated properly. But I doubt that. The problem sounds like the tube arched because it has a short. You can try the tube again but if I heard the pop again I would remove the tube permanently. A tube with a dead short can damage your amp so be careful.

Thanks for the info. Are shorts usually caused internally in the tube, or can they be caused by the amp?

 

[drarthurwells]

Quote:

Originally Posted by replytoken Thanks for the info. Are shorts usually caused internally in the tube, or can they be caused by the amp?

Internally in the tube.

Sometimes I get static or scratchy noises which go away when I gently rock the tube in the socket to get better pin contact. Buzzing or ringing noises may be a short in the tube. If a tube glows unusually it could have a short - turn off, let cool, and remove/discard such tubes.

Clean pins at times with a wire brush or fine metal sandpaper.

 

[sacd lover]

Quote:

Originally Posted by mattigol Don't mean to thread-jack, but I have a 6SN7 tube (actually two) that display a weird on-and-off buzzing sound occasionally, on top of a ever so slight, but permanent static noise on on channel only. The buzzing really reminds me of an insect flying buy. Logic tells me the amp or tube seating should be at fault (with two tubes displaying the exact same behaviour). However, a third tube from a different manufacturer doesn't show any of this. I have already cleaned the tube socket.

Clean the actual tube pins of the tube. A wire brush will clean the pins on a 6sn7 right up. If that doesnt work there is probably a problem inside the tube. But this sounds like dirty pins not making proper electrical contact.

 

[beerman21]

Quote:

Originally Posted by mattigol Don't mean to thread-jack, but I have a 6SN7 tube (actually two) that display a weird on-and-off buzzing sound occasionally, on top of a ever so slight, but permanent static noise on on channel only. The buzzing really reminds me of an insect flying buy. Logic tells me the amp or tube seating should be at fault (with two tubes displaying the exact same behaviour). However, a third tube from a different manufacturer doesn't show any of this. I have already cleaned the tube socket.

I've had a problem with some poorly stored tubes from the 40's where the dab of solder holding the internal wires to the pins corroded and cracked apart. There was a buzzing sound alright but that was the least of my problems since the tube went dead at the same time. Luckily it didn't damage anything and the tube worked fine after I reflowed the solder on the pins.

 

[mattigol]

Mucho gracias, as always!

 

[creeky]

As others have suggested clean the pins on the 12AX7 also check the sockets. I had a valve go bad in one of my amps and without me knowing it cooked one of the contacts causing a crackling sound with some but not all valves.