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Re: OR120 extremely asymmetical output

9/8/2005 2:23 AM
Re: OR120 extremely asymmetical output
Don't just throw parts at it. Did you check the bias on ALL the tubes? Never check just one and assume the rest are the same just because they are matched. If all the tubes bias up OK, but it goes to cherry red shortly thereafter, what is the current at THAT point? I would monitor the grid voltages on this. if they are say -50 to start, are they still -50 when red plating occurs? if the voltage fades away, then the bias fades with it and the tubes will run away. If that is happening, I would check out the interstage caps from the PI. The tubes themselves could have an issue, so try a different set. Even new tubes from a reputable dealer can have a clinker in the bunch.