Any thoughts? Laney Cub 10 keeps dying out on me...

[jonny]

Hey, everyone, I usually hang out in the luthier's corner, but I have an amp problem.

About two months ago I bought a new Laney Cub 10 from a local store. In the past couple weeks, it's been doing this thing where suddenly it dies out. No static, or popping or anything, it just quickly loses volume and the light on top fades out, over a bout ten seconds, then its dead. When I turn it off and turn it on a minute later, sometimes it happens again and sometimes not. It's not from working it too hard, I'm playing at bedroom levels, and it's only after about ten minutes of playing.

Does anyone have any idea what this could be? I'm going to take it to the shop, but I'd like to have an idea of what it is before I go in.

Thanks

 

[bluesguitar1972]

my CUB12 crapped out on my at a gig the other day - I haven't had a chance to check it over much, but when I plugged it back it worked for a while, but then sounded to me like the tubes were crapping out. Hopefully that's all it is. I'm going to try another set of tubes in it and see where it takes me.

Try cranking yours up once it's warm and see if the tubes are farting out.

 

[tazzboy]

When's the last time you had the amp re tube?

 

[bufbills]

sounds like tubes

 

[twitch]

Is the power indicator the light thats fading? If so, you have a power supply issue. If its one of those click on/off switches it could be the issue. Im not familiar with this amp though. If it has a power tube failure relay like the ENGLs do, then it could be a power tube issue as well. More info is needed. Ill see if I can find some info on it.

 

[twitch]

Well I see it has a toggle switch for power, so Im gonna go out and say your switch isnt the problem chances are. The manual doesnt go into detail about any kind of tube failure mechanism. My next guess would be a bad capacitor somewhere in the power supply section. If that jewel light on top, which is the power indicator, is going out, that means for some reason your losing AC power somewhere between the jewel light and the wall. If it were a tube issue, the light would stay lit and youd have no audio. However, if there is some kind of resetable tube failure mechanism thats shutting down the amp to protect it because it notices a fault in a tube, that could be the issue, but as stated, the manual says nothing about this. Id have to have further detailed details or a schematic to know for sure one way or the other.

 

[qpHalcy0n]

Because you said the pilot light is going out as well it may be something more sinister going on there...or not. The pilot light in that amp is run off of the 6.3V tap on the PT. It has a 6A resettable fuse on the line with it. This fuse toggles between states when excessive current is pulled through it.

Its possible that you have a tube who's heater is drawing excessive current which would indicate that something is shorting when hot. So what I would do is pull every tube in the amp and turn it on...see how long that will last you. If the jewel stays on start putting tubes back in one by one and see if one of them causes the problem (test them all). If several different tubes bring this about, then I would not suspect the tubes. I would suspect a shorting PT secondary. If one of them is clearly the suspect, then ditch it and get another....then see what happens. Essentially, test every tube individually to see if one stands out. If so thats your suspect. If a couple of them or ALL of the tubes individually cause the problem then chances that all of your tubes being bad is so unlikely as to not be the cause.

If not, I would suspect a shorted 6.3 secondary winding on your PT.

 

[twitch]

Because you said the pilot light is going out as well it may be something more sinister going on there...or not. The pilot light in that amp is run off of the 6.3V tap on the PT. It has a 6A resettable fuse on the line with it. This fuse toggles between states when excessive current is pulled through it.

Its possible that you have a tube who's heater is drawing excessive current which would indicate that its likely shorting when hot. So what I would do is pull every tube in the amp and turn it on...see how long that will last you. If the jewel stays on start putting tubes back in one by one and see if one of them causes the problem. If so, trash it and get another. While you're at it, be sure to check all of them.

If not, I would suspect a shorted 6.3 secondary winding on your PT.

Well, there you go, someone must have a schematic . Thats an interesting way to do tube failure protection. Cool.

 

[jonny]

Thanks guys, I knew this was the place to come

I had figured something like that, since it is the whole that's turning off, not just tubes.
This is my first tube amp, so I want to be pretty cautious if I start pulling tubes out.
qpHalcy0n, did you mean take all the tubes out at once?

 

[qpHalcy0n]

Yes, with the amp off pull all of the tubes. Turn the amp on and let it run. If nothing happens after awhile, add the tubes in one by one each time letting it run for awhile. If you encounter a tube that causes the problem then note it. Since you do not have a standby switch, it's ok to add the power tubes in pairs (which would mean both of them).

You're basically doing a process of elimination here. If the problem persists with no tubes in the circuit or if all of the tubes individually are OK but when added in together cause a problem then i'd be weary of your PT. I don't want to have you rummaging through the insides so this is a simple test that won't harm the amp and wont expose you to any dangerous situations but will help in getting a little closer to the problem.

 

[jonny]

Alright, I'll give it a shot, thanks a lot.

 

[RoldanRoll]

I got the answer

thermal fuse...

And I got the solution ...

a variable tagged TR1 inside... turned it off (fully counter clockwise) and ... BINGO!!! Perfect sound again ... i've been playing loud since i woke up this morning...

I'll tell you more later... (i'm supposed to be working)
I hope this works for others
Saludos from Medellin Colombia

 

[RoldanRoll]

ooops...
i checked it as I re-install in case and it is TR2 (not TR1) ... sorry
but anyway it is working fine
Saludos

 

[dace2903]

ooops...
i checked it as I re-install in case and it is TR2 (not TR1) ... sorry
but anyway it is working fine
Saludos

I had a similar problem... but my Cub 10 doesn't dies out, it just has a hum. it's horrible I don't know exactly what it has, it starts all right, but when it warms up starts to emit that disgusting hum and intensifies when I roll any knob of control on te amp (tone, volume or gain). I have understand that if it were a tube problem (I mean, at least damaged) it wouldn't sound, but the performance is like always except for the HUM!!!, if anyone can help me whit this I will apreciated a lot, I'm a little worry about it

 

[slagg]

bad/cold solder joints on your heater traces.needs reflow on all to be sure.Your welcomethis is why it works fine when it cools off.The first thing I do with any mass produced amp.

 

[rjudo]

I got the answer

thermal fuse...

And I got the solution ...

a variable tagged TR1 inside... turned it off (fully counter clockwise) and ... BINGO!!! Perfect sound again ... i've been playing loud since i woke up this morning...

I'll tell you more later... (i'm supposed to be working)
I hope this works for others
Saludos from Medellin Colombia

I had the same problem with the cub 12, apparently it is a common issue with these.

 

[mpaulb1386]

Hey not sure if this has been covered yet but I remember reading somewhere that those heads had some kind of thermal switch in them that was meant to save the amp if it got to hot. I understand that some of these where faulty from the factory.