Wrong Bias in HD 210

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Author Message   thefishingline Posted on Tuesday, February 10, 2004 - 10:22 pm:    I just boght a HD210 and have the famous Jess Oliver looking at it for me. He has discovered that whoever put in the brand new ET-E34Ls's also changed the bias and he said it is wrong. While the overall amp output is within 1/2 of one watt of the oter one I have...the bias is wring and he to change it back. Why do people change the manufacturers bias settings?   Terry Posted on Tuesday, February 10, 2004 - 11:14 pm:    Everytime you put new tubes in, you have to check the bias and reset it. And even every six months, if you are playing alot, it should be checked.   thefishingline Posted on Friday, February 13, 2004 - 07:02 am:    Does the same thing have to be done in a fender twin as well? If I put a new set of tube sin and change the bias to match to be correct...and I replase those tubes with the same tubes..it has to be done again? I thought the amp came from the facotry set wiht a set of tubeds and I would keep using the same tubes wouldn't I?   michael kaus Posted on Thursday, February 19, 2004 - 07:01 am:    Think of the bias setting as a valve. Each tube has it's own current draw and the bias setting is the valve that regulates the amount of current passing. This is very important in MM amps as they have very high plate voltages. If you you have no bias voltage, the tube goes into runaway and burns up. Yes, you should have the bias set on MM amps and Fender twins unless it has been converted to cathode biasing. Brand of tubes meens nothing and even with the same brand, each tube has to be checked for current draw. That's why when you buy matched tubes, you still have to bias the amp. Just both tubes pull the same. MIke.