Issue wit tube head

[glennvalentine]

Can't seem to figure out what the issue is. I have a Carvin Legacy II that fizzes out and drops to about 1/4 power/volume after playing for 15 or so minutes. I thought it was an internal loose connection so I ran the head off the cab, on a separate surface. Still did it. I've also plugged the guitar into the effects loop return immediately after it happens and I get pull power there. I assumed it was in the preamp section but when I plug the guitar into the input right after it's been in the effects return I get pull power on all channels again. This is with no breaks in between. (Plug into the return, full power, 3 seconds later I plug it back up front and I'm at full power.)

Any thoughts on this?

 

[jon the art guy]

Re: Issue wit tube head

Preamp tube gone bad?

 

[Gone_Shootin]

Re: Issue wit tube head

Preamp tube gone bad?

That's my thought as well. OP, take a known good 12AX7 and try it in each position in the preamp.

 

[BrianS.]

Re: Issue wit tube head

Try cleaning all the jacks with contact cleaner.

 

[zzmoore]

Re: Issue wit tube head

Preamp tube gone bad?

I would try this first.
Otherwise, unfortunately, this is the classic symptom of a cold solder joint. Something in the amp that draws enough current to get hot will do so. After it plays for a while, the lead(s) on said component(s) get hot enough to melt solder and there you go....a poor connection.
A lot of times you can spot it visually. You need to pull the chassis and take a look.
I do not know how "user friendly" these amps are. The same thing can happen with any type of slide-on connectors.
Maybe check on the Carvin Forum...see if your amp model has a reputation for doing this.
best

 

[jackson111]

Re: Issue wit tube head

have you tried calling carvin directly? I have never had to call them myself but on the forum people talk about problems like this and they contact carvin and they try to help you diagnose it over the phone. a lot of problems like this are usually where a ribbon cable connector that is a little loose, or the contact pins have become dirty. try taking the cables loose one at a time and cleaning the male end and female end and reseat it, also clean the send and return jacks on the effect loops. the best way I have found to clean the jacks is to spray a cable and push it in and out of the jack 4 or 5 times then repeat. hope this helps, but if it doesn't call carvin from what I have read they are very knowledgeable and very easy to work with.

 

[glennvalentine]

Re: Issue wit tube head

Thanks for all the suggestions. I'll give it a shot tonight. From what I've read the phase inverter could be the culprit. Can I run any 12ax7 in that tube slot. If I remember correctly I put an LPS at the suggestion the vendor who sold me the tubes.

 

[Edgecrusher]

Re: Issue wit tube head

Thanks for all the suggestions. I'll give it a shot tonight. From what I've read the phase inverter could be the culprit. Can I run any 12ax7 in that tube slot. If I remember correctly I put an LPS at the suggestion the vendor who sold me the tubes.

I'm not familiar with the Carvin and I dont have time to look up the schematic now but does it have a PI or does it have a cathode follower? Many people think the position is the same but its not. The LPS is recommended for the PI cause its long plates can cause harmonic and feed back problems in the gain stages... but it doesnt like the current that a cathode follower dishes out like in a Marshall. Might be something to ask about.

 

[zzmoore]

Re: Issue wit tube head

Thanks for all the suggestions. I'll give it a shot tonight. From what I've read the phase inverter could be the culprit. Can I run any 12ax7 in that tube slot. If I remember correctly I put an LPS at the suggestion the vendor who sold me the tubes.

Tubes do not usually take 10 minutes to go off...but you never know. As long as you are swapping tubes...try an AT7 in the PI.
best

 

[Gone_Shootin]

Re: Issue wit tube head

I'm not familiar with the Carvin and I dont have time to look up the schematic now but does it have a PI or does it have a cathode follower? Many people think the position is the same but its not. The LPS is recommended for the PI cause its long plates can cause harmonic and feed back problems in the gain stages... but it doesnt like the current that a cathode follower dishes out like in a Marshall. Might be something to ask about.

Very true. Russian tubes in general don't get along so well in cathode follower positions, and some buffer positions (depending on the design of the amp). That's why I just use JJs for cathode follower and buffer positions anymore, they're alot better at taking abuse.

 

[glennvalentine]

Re: Issue wit tube head

Ok so I pulled all the tubes out and then reseated the all of them. I also swapped the LPS in V5 with an GT12ax7c that I had laying around. Played for a bit and no issues. I'll put the LPS back in later to see if that was the issue or I just had a tube not seated properly. The pins on the LPS look like they are coming out of the bottom of the tube at a tiny angel, maybe 1-2* instead of perpendicular to the bottom of the tube. May have resulted in a bad connection.