Framus Cobra NOISE/weird sounds, Advice needed

[BOWIE]

You seem certain it's not a tube issue but I'll be damned if the things you describe and the noise in the clip isn't most commonly tube related. In swapping tubes, did you use all known-good pieces? Brand-new tubes can often be noisy in high-gain amps. Try them individually in V1 (the most sensitive stage) of another amp as a way of screening each one. That won't necessarily account for both triodes, but it gives you a start. The other most likely things would be a cap or resistor. You could take a look inside and inspect them for any obvious leaks, blisters, etc, but it's probably time for a tech. I've never had a cap or resistor cause the compressed sound you're describing (commonly a tube issue) but I won't exclude it.

[Ocram]

Thanks for the reply...
I changed all the 5 pre tubes with brand new JJ ECC83s (before that the amp had 4x TAD ECC83 and 1x EHECC83). Is it possible that these brand new (and different brand) tubes do the same IDENTICAL noise compared to the one the amp was doing before the tube change?
I took apart the chassis and had a look inside, didn't see anything shocking... caps seemed intact and resistors too..so yeah, guess it's time for the tech!!

[BOWIE]

Originally Posted by Ocram

Thanks for the reply...
I changed all the 5 pre tubes with brand new JJ ECC83s (before that the amp had 4x TAD ECC83 and 1x EHECC83). Is it possible that these brand new (and different brand) tubes do the same IDENTICAL noise compared to the one the amp was doing before the tube change?
I took apart the chassis and had a look inside, didn't see anything shocking... caps seemed intact and resistors too..so yeah, guess it's time for the tech!!

Yes, it's a possibility. I spend hours every week screening new/never-used tubes for noise and many of them make that exact sound (though it's more common in used pieces). Tubes only make a few types of noises and the crackle/ocean sound is one of them. However, if you don't have another amp to use for screening, save yourself any more wasted time and take it to a decent tech if you can find one. See if there's any chance you can get a flat rate for a diagnosis as some guys can spend forever chasing down a noise if they aren't experienced with a specific amp. Once it's found, the fix is almost always easy and quick. Be very specific about there being new tubes in there so that he doesn't change all of them and charge up an up-rated cost for a whole set.
Best of luck. Let us know what it turns out to be as I'll be curious.

[Ocram]

Thanks Bowie, I will bring to a repair shop to a guy who does repairs from televisions to instrument amps, will see what his opinion is first..


will keep you updated!!(I am greatly curious aswell)

[Ocram]

Amp back from the tech, unluckily the problem persist.
He said he couldn't find the real cause of the noise, he just supposes that it may be some faulty integrated circuit on the board ( 6-pin things, maybe optocouplers?? )...

He did the bias of the power tubes, only positive thing is that now the amp sounds louder at less "knob" volume, so the noise is now a minor issue while playing.

He also did a test of the "old" preamp tubes and said they're fine and I can keep them as good spares if needed.


Tho I'm still experiencing strange things:
Turned the amp on, and it had almost no volume and no gain in all of the 3 channels. Turning the volume knob on the guitar would give me A LOT of crackling/oxid-like noise. Noise (fried like) was present and consistent. Swapped the v1 with a spare one and it got way better. (gtr volume knob ok, volume and gain fine).
Then i noticed the noise would be present also with a 100% wet on the fx loop, thus making me think about a problem on the phase inverter ( tube or anything??)... I was playing and then after almost 1 hour the amp volume dropped almost to 0, so I shut off the amp. After shutting off the power, I heard strange popping sounds from the cabinet for like 3 seconds ( discharging/faulty caps?!? - I'm sorry, I dont know what it could be, just wondering ). Turned it back on, and all I could hear from the amp was a 50hz hum. Swapped v5 with a spare one and the amp worked (for an hour so far).

All this is really frustrating, is it possible that so many new/not old tubes fail randomly like that and then work fine?! If it was every other component, would the problem get better/change just swapping tubes?
I'm really hoping the problem gets costant now, because I can't bring to a tech and stay there and play for 2 hours hoping the problem will happen. Problem is that the problem doesn't seem to get consistent in time...
And I can't rely on this amp to play live because of the shame it would cause if it shuts off during a show.. :mad:

[gammalord]

Have you swapped out the power tube section? Are you certain that you've got your speaker outs/ins correct as far as impedance is concerned?

I agree with BOWIE - these symptoms really scream "tube problems" - combined with the fact that they are intermittent; most SS components will fail totally and that's that.

Take it to a different amp tech - see if Framus recommends any in your area. Those are well-regarded amps and there's no reason it shouldn't give you years of metal happiness.

[Ocram]

Hi gammalord, what do you mean with "swapping out power tubes section"? Replace the power tubes? I tried several times running "post pre" and the power tubes seem very quiet and efficient...except for the v5 fail, which seemed to resolve with a 12ax7 swap.
Impedance is right.

I will see another tech then... Could it be that it's not something directly related to the tube itself, but instead to the socket or to the solder joints that connect the socket to the board?

thanks for the reply!