Amp tech help needed here also: Framus Cobra

[Evil_invader]

Hello,

I have a wierd problem with my Framus Cobra (version 2), I already took it to the tech here, but he says everything is fine with the tubes but didn't look deeper in the circuitry. With the kind of money he charges for his work, I'd love to be able to have a clue about what might be wrong with the amp.

Here are the symptoms: Very low volume on clean channel, a lot less distortion of crunch and lead channels. Seems like I've gone from pure high gain to AC/DC type of sound (when gain is maxed)...

Every preamp tube is ok with more than 85%, power tubes are all fine..

I'm quite lost . Help please...

Thanks a lot for you time

Gab

edit: cables are all fine, guitar also, unplugged effect loop and played with its level... no change.

 

[jerrydyer]

needs new OT were you pretty hard on it ? I know those things are built tough so most likely OT, that is if a real tech says everything else is good. he didnt bother to do a simple test on the OT?

 

[Guitarzan1143]

Had a similiar problem on my mark III. Sent it in, got filter caps replaced and one of the bigass resistors. new preamp tubes made it better, but once i got it back from being serviced at mesa it was omgz gainy.

 

[sled]

Every preamp tube is ok with more than 85%

What does this mean?

 

[Oblivion DC]

Find a new tech cause the one you have now seems to suck.

 

[Evil_invader]

Every preamp tube is ok with more than 85%

What does this mean?

I'm not a tech but it seems like the preamp tubes are all working above 85% level (which seems to be an important value for the amp to work properly).

jerrydyer: OT? I don't know at all if he did check it, but wow, that would be really shitty to say the least. Hard on it? Well, not really but it recently went throught endless hours of recording before the problems occured. In fact they began to occur right when I went back to my normal setup. During the recording sessions it was working in stereo with a Bogner Uberschall.

Guitarzan1143: Thanks for the info, I'll tell him. What was your problem exactly?

Oblivion DC: He's got a really solid reputation here. He was reluctant to go deeper into the circuitry because he didn't have the wiring diagram and is not familiar with Framus amps or Soldanos (which I understood seems to be built the same way). I found the diagram and I will give it to him next time. That way he'll spend less time on it, and it costs me less.

I might need to point out the fact that I can play at loud volumes on crunch and lead channels, just not on clean. Should I play it anyway at rehearsal or shouldn't I?

 

[Guitarzan1143]

The main problem i was having was it started as light fading in/out of volume and gain... then eventually it just sunk down and stayed at the lower end of the spectrum, huge bummer. turn your amp on... put the gain/volume sort of high, plug your guitar in and keep the volume knob off, take a tiny screw driver or small long metal object, and tap your preamp tubes. if one of them rings through the speakers more than another, you need to replace it. best way to tell in my opinion.

 

[Sixtonoize]

needs new OT were you pretty hard on it ? I know those things are built tough so most likely OT, that is if a real tech says everything else is good. he didnt bother to do a simple test on the OT?

A bad OT won't cause a decrease in gain.

It sounds to me like he's got a bad preamp tube somewhere or a bad solder joint.
Since solder joint problems tend to be intermittent, I'm guessing it's a bad tube.

Buy a new preamp tube and swap out the existing preamp tubes one at a time to see if it fixes the problem.
It's not guaranteed, but you just may solve your problem for under $20.

 

[sled]

Every preamp tube is ok with more than 85%

What does this mean?

I'm not a tech but it seems like the preamp tubes are all working above 85% level (which seems to be an important value for the amp to work properly).

Maybe I've missed this test in my 35 years of amp work, but I wouldn't put any stock in that number.

You think the amp is not working correctly yet your amp tech says it's Okay. Did you two discuss and analyze your amp together while you were playing it? If the tech wants to charge you for this time, seek another amp tech.

 

[Evil_invader]

Sixtonoize: Great if it's not the OT. I tried to swap preamp tubes myself before taking it to the tech, but no result, the problem is still there. Maybe it's a solder joint as you say.

Guitarzan1143: Here it was like day and night from one rehearsal to the other. Preamp tubes were said to be fine but I'll check again for sure.

Mood Bender: About the 85%, I have no clue, honestly. I know he's been in this business for long as well, and like I said, he's got a really solid reputation, here's his website in case you want to check: http://www.chucktronic.ca/

I didn't really discuss with him about the amp, just told him about the problems like I just did here. I know it's not the same at all as it used to be. The difference in gain is really obvious + the volume drop on clean channel. There IS a problem. That's obvious.

He charged 15$ for checking into it and said he'll cahrge me 15$ less if I bring it back.


Thanks a lot for your help all, it is really appreciated. Keep the hypotheses coming please.

 

[sled]

If he won't spend time with you off the clock to get calibrated, go to another tech.

 

[glip22]

Definitely replace the phase inverter tube. Replace and rebias power tubes. Believe it or not it could be a fuse. Sometimes the mains or HT fuse could actually be compromised but still be making contact. Vibration can then cause the amp to go in and out. So just replace the fuses. It's cheap and easy enough. Doesn't sound like an OT to me, but you never know.

 

[JerryP]

If the tubes have been checked by someone that knows or changed with known good tubes I would say find another tech. Beyond tubes there is nothing simple inside there for an owner to repair. It's probably not the OT.
Jerry

 

[glpg80]

If the tubes have been checked by someone that knows or changed with known good tubes I would say find another tech. Beyond tubes there is nothing simple inside there for an owner to repair. It's probably not the OT.
Jerry

is what i am thinking. the next steps of troubleshooting will take some voltage probing and/or some time with signal injection if the filtering stages check out, and tubes are also not to blame.

last time i had a problem like this it was a bad relay, caused by a loosely soldered transistor that wasnt supplying power when it was supposed to. but there is no telling what is going on over the internet - the circuit needs to be on a tech bench.

get a new tech.

 

[glip22]

Send it to Jerry(FJA). Guarantee you he will fix it and he won't rape you while doing it.

 

[JohnnyC]

when you replaced the preamp tubes...did you just yank them out and push new ones in??

maybe try using some electrical contact cleaner and slightly "rotating" (once the pins are in a slight wiggle/swirling motion) the preamps in just ot make sure the sockets are making proper contact.

 

[Evil_invader]

when you replaced the preamp tubes...did you just yank them out and push new ones in??

maybe try using some electrical contact cleaner and slightly "rotating" (once the pins are in a slight wiggle/swirling motion) the preamps in just ot make sure the sockets are making proper contact.

Only swaped them and added one known good one on and off during the process.

I will go at the tech again with wiring diagram. Hope it's only a resistor or something like that.

Thanks a lot for your help everyone!

If anyone have had a similar problem or thinks he knows what might be happening, tell me!

 

[sschultz242]

Keep us posted on what the problem was if you get it fixed. My buddy has a cobra that is doing the exact same thing and had the exact same problem with the tech. So at least let me know if not everyone lol

 

[Evil_invader]

Really?

Please PM me contact of your friend!