Tube Amp static/Noise

  • Thread starter Thread starter Wireneck
  • Start date Start date
Wireneck

Wireneck

New member
I've got a Framus Cobra that I am getting ready to put up for sale but I want to make sure that it is in tip top shape before it leaves my hands. Lately I have been getting a little bit of a static sound which is most noticeable on the clean channel if I am not playing and sometimes while playing. It can be heard on the distorted channel as well but only when I am not playing that I can tell. The distortion makes it much harder to hear.
I am assuming that I have a tube that is going bad but where would you guys start? Should I be suspect of the preamp tubes or could this be a power tube issue?

any ideas are appreciated
 
It is definitely coming from the amp. I can roll the volume knob back on the clean channel and as long as the amp isn't in standby mode, I can hear it. It is very faint compared to the actual guitar signal but it is there none the less. This is a pretty expensive head, I just don't want to risk any bad feedback or complaints on something that I can take care of ahead of time.
 
Some preamp tubes can produce static and pops. Take a tube that you know to be good and swap them one at a time. Start with the preamp tube closest to the input.
 
ocnor said:
Some preamp tubes can produce static and pops. Take a tube that you know to be good and swap them one at a time. Start with the preamp tube closest to the input.
Click to expand...

I agree with ocnor, and it could be loose tubes in their sockets too.
 
Wireneck said:
I've got a Framus Cobra that I am getting ready to put up for sale but I want to make sure that it is in tip top shape before it leaves my hands. Lately I have been getting a little bit of a static sound which is most noticeable on the clean channel if I am not playing and sometimes while playing. It can be heard on the distorted channel as well but only when I am not playing that I can tell. The distortion makes it much harder to hear.
I am assuming that I have a tube that is going bad but where would you guys start? Should I be suspect of the preamp tubes or could this be a power tube issue?

any ideas are appreciated
Click to expand...
Wireneck, sounds like you have a power tube that is microphonic.Remove
any covers or what-not to expose the tubes.Make sure all of the tubes are
well seated.With nothing plugged into the amp turn it on and crank it up a bit.
Tap each tube with a pencil.If you hear the tap thruogh the speaker, then the tube is microphonic.Do the same with the pre tubes.
If they are the original power tubes, be careful when you handle them.A lot of high end amp makers put grade #'s on them.If they are graded you can
order the power tubes from the builder w/o having the amp biased.
 
ocnor said:
That is a bad idea as you can damage the tubes accidentally. Also a tube does not need to be microphonic to be heard through the speaker when tapped.
Click to expand...
Tapping the tube with a wooden pencil or dowl is standard practice.It wont
hurt the tube.(I said tap, not knock the shit out of it.)
If you can hear the tap through the speaker, the tube is microphonic.If you can hear a pencil tap through the speaker, then you can bet your ass that
when you put signal to the speaker, that tube is gonna be ringing like a bell
or causing some type of unwanted noise.
 
Had this happen with my Princeton Reverb once. Check each tube's pins. If you get a little gunk on the pins it will cause this.
 
SHEPPARDB. said:
Tapping the tube with a wooden pencil or dowl is standard practice.It wont
hurt the tube.(I said tap, not knock the shit out of it.)
If you can hear the tap through the speaker, the tube is microphonic.If you can hear a pencil tap through the speaker, then you can bet your ass that
when you put signal to the speaker, that tube is gonna be ringing like a bell
or causing some type of unwanted noise.
Click to expand...

This is from thetubestore.com:

"All tubes will exhibit some degree of microphonics. Microphonics do not mean that a tube is unusable. You just have to screen them a little closer and determine where they are best suited for use. Input pre-amps are the most sensitive areas of the amplifier. When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Keep in mind that doing so can actually damage the tube and make it more microphonic or cause it to fail if you hit it real hard. Although they are screened prior to shipment a tube is an electromechanical device and can be damaged during shipment. A microphonic tube will ring, howl or produce general feedback problems. It will be more noticeable at louder volumes or when used in close proximity to a speaker, typically in combo amps. If the tube has good tone at lower volumes and is free from unwanted noise, you use it in a less sensitive part of the circuit, such as tone recovery or phase inverter applications.

Noise is more of a problem than microphonics. A noisy tube will make random popping noises, crackle occasionally or just hum. All tubes have a certain noise floor; this is the inherent background noise that the tube makes in operation. Typically, you will notice this as a soft hiss or "white noise". Tubes designed for high gain can exhibit more background noise. Other components can cause noise problems that may be blamed on a bad tube. Plate resistors are notorious for causing hiss and crackling as they age and begin to fail. A new tube may better amplify these defects, so try substituting another new tube to be sure of the source of the noise."
 
Thanks guys I will try some of these suggestions and report back. The noise is a very light crackle/pop sound. I have some spare pre-amp tubes somewhere, so I will see if I can't narrow this down.
 
ok still getting the small pop/crackle with the master volume all the way down and no guitar plugged into the input. Does this pretty much make the power tubes suspect?
 
Wireneck said:
ok still getting the small pop/crackle with the master volume all the way down and no guitar plugged into the input. Does this pretty much make the power tubes suspect?
Click to expand...


Did you pull each tube and check the pins? What you're describing is exactly what happened to mine before and it was just some dirty tube pins.
 
yeah I pulled them and checked the pins and then reseated. I guess I will be taking this one in to the tech before I put it up for sale. bummer
 
Wireneck said:
yeah I pulled them and checked the pins and then reseated. I guess I will be taking this one in to the tech before I put it up for sale. bummer
Click to expand...

it's not the pins... it's the socket that ya need to check... and dont assume that it's ok just cause it feels tight when you insert... you can have several connectors be tight and feel good overall and still have several that dont make at all... power down let sit or drain the caps... take a little screw driver (i use a dental pick) and close up the little connectors within the socket...

does it increase and/or crackle as ya turn nobs??? this can be a sign of coupling cap problems... especially in the tone circuits...
 
dementedchord said:
it's not the pins... it's the socket that ya need to check... and dont assume that it's ok just cause it feels tight when you insert... you can have several connectors be tight and feel good overall and still have several that dont make at all... power down let sit or drain the caps... take a little screw driver (i use a dental pick) and close up the little connectors within the socket...

does it increase and/or crackle as ya turn nobs??? this can be a sign of coupling cap problems... especially in the tone circuits...
Click to expand...

+1

Another good thing to do is take a old tube that fits the socket and spray the pins with contact cleaner. then insert and remove in each socket a few times to clean them.
 
Thanks for all the help and tips guys. I am still getting the noise so I think I am going to drop it off at the tech on monday.
 
Arcaxis- In this case I am fairly certain that it is the amp. I own two others that are plugged into the same power strip and are don't demonstrate any of these symptoms. I bought this house about two years ago and I haven't had any other noise problems, including using this amp in the same room. It has been a while since I used the Framus in a live/band setting but I remember hearing a milder version of the static/pops in between songs at one of our last rehearsals but we play pretty loud. I am usually positioned right next to our Keyboardist who uses vintage Moog synths which are subject to all sorts of noise and hiss on their own haha. I just assumed it was him. Getting the amp back here into a much more controlled listening environment revealed that it was in fact me. I appreciate all of the help and suggestions. Hopefully it won't be too pricey of a fix. Either way I will feel much better about selling an amp that I KNOW has a clean bill of health.
 
ocnor said:
This is from thetubestore.com:

"All tubes will exhibit some degree of microphonics. Microphonics do not mean that a tube is unusable. You just have to screen them a little closer and determine where they are best suited for use"
Click to expand...

No jab at you man, but that is bullshit.The fact that the info comes from an on line tube store makes it all the more so.All tubes are not microphonic.Bad
tubes are microphonic.A microphonic tube IS not unusable if you care about how you sound when playing.
You can order tubes online or get them at a local store.Most will be micro--
phonic off of the shelf.(especially true with preamp tubes)thetubestore.com
put that bit of myth on the site in the hope that you would take it as truth and not return the defective product that they sold you.
i always change pre tubes in the store that I buy them from and check to
make sure they are O.K.(with my pencil)I,ll change a power tube in a pinch
but I would prefer a Pro do it and bias.
Your method of checking tubes is most definately valid.Misfortune always
has my tubes being fucked during a late sound check with 30 mins before
I have to play, so the pencil trick works for me.

Take it easy,
Shep
 
Just wanted to give everyone an update. I took the amp in to my tech. It turns out that my power tubes were definitely in bad shape (as suspected) but I also had two preamp tubes that were going microphonic. Granted, I started swapping preamp tubes around with spares trying to get rid of the noise and there is a strong chance the preamp tubes I had weren't in the best of shape. I've got to start keeping better documentation of the spare parts I have laying around here.
So I ended up getting all of the power tubes replaced, having the amp rebiased and swapping out the bad preamp tubes. This is the best that the amp has sounded since I bought it. For the mere $150.00 it cost, I am seriously kicking myself in the ass right now for not having this done when I bought the amp. I used it at rehearsal over the weekend and I think I am actually not going to sell it right now.

thanks again for all of the info and help.
 
arcaxis said:
Also if you have an AM band radio that plugs into an AC outlet, tune it to where there is no station, turn up the volume, and see if you here any crackles and pops similar to that hear from your amp. Sort of an unconventional way to troubleshoot, but if somethings arcing and sparking an AM radio may pick it up.
Click to expand...


thats brilliant! never thought about trying that!
 
You must log in or register to reply here.
Back
Top