Amp issue, newbie help please! (weird noises)

[Raccio14]

Every here and there, my amp will make a bit of a hissing while I'm playing, and lose some of the bottom end oomph, almost sounding like it's being heard through plastic. It's really weird and only happens here and there (maybe about 1/10 of the time I'm playing), and it's really obvious to me when it stops and starts back up again.
Thus far I've found no rhyme or reason to it, and it happens with both of my basses. They're plugged straight into the amp (no pedals or stuff) so I'm pretty sure it's the amp causing the issue.

It's an Ampeg BA-115T combo, and only a couple of years old, so I really don't know what the issue could be.

Any help?

 

[Raccio14]

.... Anyone?

 

[jelwood]

Is there any way you know of to make it do that? Like, does it happen when you do a certain thing with your bass or eq?

 

[Raccio14]

nope. it happens completely spontaneously and randomly. I don't touch anything on my EQ or anything.
It's happened just in the middle of me playing something; it sounds fine, and then all of a sudden, it just gets that weird plastic-y sound.

 

[5port]

nope. it happens completely spontaneously and randomly. I don't touch anything on my EQ or anything.
It's happened just in the middle of me playing something; it sounds fine, and then all of a sudden, it just gets that weird plastic-y sound.

Replace 12AU7. Sounds like a gassy tube. Even new tubes can be gassy.

 

[Bassmec]

Replace 12AU7. Sounds like a gassy tube. Even new tubes can be gassy.

Yes I would change the specially selected Kazakhstan 12AU7
for a new old stock Mullard, RCA, Telefunken, Valvo, Brimar,
Amperex ETC.
Not that I have any problem with asia new production tubes they can be really quite reliable, there is always one or two
produced per week that will stand the test of time.

 

[Raccio14]

Thanks guys. Anything I need to know to do this on my own? Or should I just look into ordering a new tube online and go for it?

I do have a decent history with electronics, and build computers, so I doubt Ill have too much trouble figuring it out. Amps are just new territory for me.

Also, is there a difference between the replacement tubes I buy? I realize it will have to fit the 12AU7 spec, but are there different variations? and which one do I want?

 

[Raccio14]

...???

 

[standupbassman]

I'm not a tube guy so i couldn't tell you about if it's bad tube (everyone else said it is so it probably is) but I've had bad power connections and bad instrument output/input connections make all sorts of crazy noises. Also, a dirty volume pot might makes a hissing noise sometimes.

 

[christw]

Have you tried swapping cables and basses? I wouldn't go switching parts until you're sure it's the amp.

 

[Raccio14]

I'll double check with the cable, but I've never had a cable do anything that crazy. And I'm pretty sure two volume pots didn't go bad spontaneously at the same time.

 

[Raccio14]

So I did test cables, and that's not the issue. It's most clearly the amp, and as far as tubes go, i'm really without a paddle on what to get/do. Again, it can be described as a harsh distortion or buzzing with a loss of depth from the bass, and it's rather random and seems to have different severity on differing occasions.

 

[RickenBoogie]

Take it in to an amp tech, shouldn't cost much at all to replace a preamp tube, and having it checked out you'll know for sure it's good to go.

 

[Raccio14]

Take it in to an amp tech, shouldn't cost much at all to replace a preamp tube, and having it checked out you'll know for sure it's good to go.

Blah, maybe. I hate not being able to do **** myself

also, if I can avoid transporting this big thing, I'd rather not.