Amp help - malfunctioning tubes ?

Benny Hicks · 01-28-2004, 03:58 PM

I use a Carvin Nomad 112, and it has four EL84's and five 12AX7A's. When I play a lower note by itself, such as an A on my low E string, it like splits it into two octaves. I can hear the A and also an A that sounds like it's an octave higher. Is this a problem with the tubes, or maybe the pickups?

Ben

PianoMan · 01-28-2004, 04:39 PM

Or did someone hide an octave pedal inside the amp...

Benny Hicks · 01-28-2004, 04:54 PM

Quote:

Originally Posted by PianoMan

Or did someone hide an octave pedal inside the amp...

Unfortunately it can actually sound like this at times

Too bad it's not that easy...

Ben

Major Tom · 01-28-2004, 06:01 PM

I am assuming it does this with just a guitar + cord +amp setup; no pedals, right?

I don't know what would cause that, but tubes go bad in different ways, it could be one of them has gone awry.

Reverb - could be something goofy with the reverb circuit (assuming it has one). Turn it all the way off and see if it still does that. Most modern amps use SS circuitry for the reverb, but since yer Nomad has 5 preamp tubes it may be all tube reverb...?

Preamp tubes - put your spare 12AX7 in each position and see if it is one of them.

Power tubes - if you have a spare, do the same thing. If not, you can pull out one pair of the power tubes on most 4-power tube amps, the one exception I know of is the PV Classic 30 since its power tube filaments are wired in series. It won't hurt the amp either way, if they are in series and you pull a pair you just won't get any sound. Anyway, the pairs are the 2 inside (2 & 3) or the two outside (1 & 4). Pull out the 2 inside tubes, reapply power, see if it still does that. If so, put them back in, and do that with the 2 outside tubes. If it doesn't do that, replace that pair of EL84s.

Other than that, I have heard that when the power supply filter caps get old/weak, the symptom is "ghost notes", but I don't think they are an octave above the fundamental...

Don't hesitate to call or email Carvin's tech support - it could be something they have encountered before.

Maestro_dmc · 01-28-2004, 06:06 PM

Do you get this at all volumes, or just when you play loud?
Have you really abused this amp? Are you the original owner, when was the last time it was re-tubed?

Is this sound one that anyone would notice right away, in other words, does it sound like something is wrong?

You may have a tube or two going "microphonic" on you. Try tapping lightly on the tubes, one by one with a pencil eraser, while the amp is turned up to a decent volume. A bad one should ring fairly load when you tap it.

Is it possible you are just hearing the harmonic? There is actually what you described and more already going on with any stringed instrument that you play. The fundamental, and the octave harmonic above it are audible if you know what you are listing for.

Major Tom · 01-28-2004, 06:21 PM

Quote:

You may have a tube or two going "microphonic" on you. Try tapping lightly on the tubes, one by one with a pencil eraser, while the amp is turned up to a decent volume. A bad one should ring fairly load when you tap it.

Yeah, that is a strong possibility. All tubes are a little microphonic, but one that would do something like that should stand out from the others. Turn it up all the way, with nothing plugged in for the tap test. I had one set of power tubes (I guess only one did it, but I replace 'em in pairs) that got wierd with some kinda microphonic noise that only happened after they had been on for 10 or 15 minutes...

Don't forget to turn the amp off when changing tubes...

Quote:

Is it possible you are just hearing the harmonic? There is actually what you described and more already going on with any stringed instrument that you play. The fundamental, and the octave harmonic above it are audible if you know what you are listing for.

True, but of course it would not sound like an octave pedal either. Also, are you standing really close to it, with it up pretty loud?

PianoMan · 01-28-2004, 09:56 PM

I had an idea. Do you have a multi effects unit? I was playing around with one at a music store a few weeks back, and I started playing around with the harmonics button. When it was turned on, on certain notes and most 2+ note chords/intervals I would get an octave effect of a sort. If you have a multi effects unit with this, check to see if it is on.

Benny Hicks · 02-04-2004, 02:51 PM

Quote:

Originally Posted by Major Tom

I am assuming it does this with just a guitar + cord +amp setup; no pedals, right?

No, I use a TS-9 and a DD-5, but they definitely are not the problem.

Quote:

Originally Posted by Major Tom

Also, are you standing really close to it, with it up pretty loud?

I was only like four feet from it and it was at about 10 o'clock. Do you think it was just natural?

Quote:

Originally Posted by Maerstro_dmc

Do you get this at all volumes, or just when you play loud?Have you really abused this amp? Are you the original owner, when was the last time it was re-tubed?

This occurs at higher volumes but is only noticable when I'm soloing on a lower string. The amp is less than a year old and I bought it new direct from Carvin.

Quote:

Originally Posted by Maerstro_dmc

Is it possible you are just hearing the harmonic? There is actually what you described and more already going on with any stringed instrument that you play. The fundamental, and the octave harmonic above it are audible if you know what you are listing for.

This is definitely a possibility.

Quote:

Originally Posted by PianoMan

Do you have a multi effects unit?

Nope, I'm a tonal snob

Ben

Major Tom · 02-04-2004, 04:58 PM

Could just be the natural distortion... Sometimes when I listen to a guitar tone from an AC-30, like some of the old British invasion stuff, it will sound a little bit like an electric 12 string in places since that amp is so "rich" in harmonics...