Kustom Defender Amp - overheating?

[Nevil Bamshoot]

I've been using a Kustom Defender (http://www.kustom.com/product_detail.aspx?TypeID=2&FamilyID=75&ProductID=100) 50 watt tube amp for about 8 months now, and I've had a few problems. Wondering if anyone can help me with any advice. Beginning of August (4 months after purchase) a power tube (EL34) blew, so I got that replaced. Sounded great, everything going fine.

Then at my last 2 rehearsals, after about 3 hours of playing, the thing started sounding very broken - static, barely any of the signal coming through, cutting in and out. I looked at the back - one power tube glowing bright orange, the other looking barely lit up at all. Pre-amp tubes looked normal. I'm guessing it's over-heating, because if I shut it off and let it cool down, it starts sounding normal again. But there is obviously something wrong, and I wonder if whatever is causing this could be part of the reason it blew a tube so shortly after being purchased new. I'm going to bring it in to a tech tomorrow night, just wondering if anyone has any advice about how to best set the bias, and whether I should be looking to get any caps replaced, or anything like that.

Thanks for your help!

[elkym]

Your tubes may be going out-- with one of them glowing orange and the other barely lit... But if they go back to 'normal' if you let it cool off, then it might be another component that's going out.

Suggestion-- if you decide it needs to run a little cooler... run a computer fan in the chassis/cab (don't point it at the tubes directly). You can run it off of the 6.3v taps-- it'll be going about half speed.

[Nevil Bamshoot]

Your tubes may be going out-- with one of them glowing orange and the other barely lit... But if they go back to 'normal' if you let it cool off, then it might be another component that's going out.

Suggestion-- if you decide it needs to run a little cooler... run a computer fan in the chassis/cab (don't point it at the tubes directly). You can run it off of the 6.3v taps-- it'll be going about half speed.

I've thought about that, but then I did some reading that seemed to suggest it might be biased incorrectly if this is happening. I just don't know jack about what bias setting to request from a technician. And I shudder to think what the people I'm going to (in W'burg, Brooklyn, NY) would charge me to install a fan...thanks for the suggestion though, I will think it over.

[TweeDLX]

As elkym suggested, you probably have other issues besides incorrect biasing. Swap the power tubes with each other to see if the problem follows the tube or is specific to one particular tube socket. If it follows the tube, you have bad tubes. If it doesn't, you have more serious issues. Possibly a bad screen grid resistor.

Mike

[Nevil Bamshoot]

As elkym suggested, you probably have other issues besides incorrect biasing. Swap the power tubes with each other to see if the problem follows the tube or is specific to one particular tube socket. If it follows the tube, you have bad tubes. If it doesn't, you have more serious issues. Possibly a bad screen grid resistor.

Mike

Thanks, I'll try switching the tubes before bringing it into a tech. That makes sense. Thanks to you both!