• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

problem: half power on push-pull ?

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vlljpior

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Joined 2004
#1
Hi, i have a problem with my amp. I was playing guitar and suddenly, half of the power was gone. I heard like a bad connection go: signal was up down up down. And One of my power tube was very red...

So, Only one of my power tube is working. When i change the tube the same problem come out. Just one of my phase is working.

I check for a bad connection: nothing.

If i keep only the faulty phase: i heard a little bit of the sound, like it was only the preamp driving the speaker...

Is it my phase inverter tube faulty. I use a 6sl7 octal tube. Can A HALF OF THE TUBE BLOW UP ?

Or what can else ?
 
#2
vlljpior said:
Hi, i have a problem with my amp. I was playing guitar and suddenly, half of the power was gone. I heard like a bad connection go: signal was up down up down. And One of my power tube was very red...

So, Only one of my power tube is working. When i change the tube the same problem come out. Just one of my phase is working.

I check for a bad connection: nothing.

If i keep only the faulty phase: i heard a little bit of the sound, like it was only the preamp driving the speaker...

Is it my phase inverter tube faulty. I use a 6sl7 octal tube. Can A HALF OF THE TUBE BLOW UP ?

Or what can else ?
Click to expand...


You may have lost a coupling capacitor on the Control Grid of one of your output tubes. That would explain why one output tube is working and one output tube is "very red".
 
#4
vlljpior said:
Hi, if i swap the output of the phase inverter that go to the power tube, my problem go to the other power tube. So the problem came out of the same half of the phase inverter tube.
Click to expand...

I don't think problems come from tubes: first check all the resistors for overheat, caps for shorts, sockets for arcing, bias pots for aging and bad contacts, or just refer to a qualified amp tech (not to offend, we're all about diy, but in a tube amp there are dangerous voltages...)
 
#5
trouble found

I just found that was the couplig cap at the input of the power tube was in trouble, at the grid, was faulty. I changed it. The amp work like a new.


You know, when you enter in the tube amp world, you have to deal with some new problem and be helping be other with more experience.

thanks
Dan
 
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