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Output Tube Bias Problem

65.146.233.101

Posted by Msquared on February 4, 2006 at 06:18:36

I have a CJ Premier Eleven-A (I am the original owner). I have had absolutely no operational problems with this amp since day one. I recently purchased a new quad of SED 6550s from a "mainstream" tube source from whom I have purchased over the last several years many new production and NOS tubes with no duds. After installing these new SEDs I discovered that I was unable to properly adjust the bias. Even with the bias adjustment pots turned all the way down the bias indicator LEDs on my amp remained lit. After thirty seconds, I also noticed that the plate on one of these tubes began a dull red glow. I immediately turned the amp off and contacted the dealer. He suggested that this set of tubes may be too "hot" or have too much gain for my amp. At the dealer's suggestion, I have returned the tubes and am currently awaiting a replacement set selected for lower gain. My question for the experts: Is this a common problem? Are some of the new-production SED 6550s too "hot" for some amps? Is there a possible fault with my amp? The amp continues to work flawlessly and is easily biased with an older set of SED 6550S as well as my set of low-hours "pre-NATO" EI KT-90s. Any ideas or suggestions? Thanks in advance.

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