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RE: The MP-1 and MP-3 servo system

Thanks for the tip. As Ralph knows and hinted at in his response, my MP1 is very old, probably mid-1990s vintage. I have owned it for more than 20 years myself. Along the way I have upgraded it in parallel with the factory but sometimes to satisfy my own whims. The fact remains that the servo is very old school. On the other hand, it has never failed to work well enough to at least shut down the DC Offset warning lights. (Typically, I have seen 4-5 mV of DC Offset per channel, which has been acceptable.) I am now working on the theory that maybe the high value resistors in series with the output of the op amp are now too high to work with the way I just recently re-set the bias voltages on the circlotron output tubes. Perhaps the resistors are dropping the V from the op amp such that it cannot fully correct the DC Offset, on the side that connects to the circlotron tube grids. (I realize that the current draw is miniscule, but there must be at least a tiny drop in V from the op amp across a 1Meg resistor. I am going to test my theory tonight (Xmas Eve). I don't expect to see Santa Claus, but I would rather that my MP1 would lose its resemblance to Rudolph, the Red LED Preamplifier. I have already proven to myself that there is nothing wrong with the op amp per se, and if it is a tube, then there would need to be at least one of the two 6SN7s failing per channel, because I also see 44mV DC Offset on the L channel.

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