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If memory serves me correctly from the last one I serviced a while back, that test point only reads the bias voltage applied to the grids of the output tubes, (-55v sounds about right, +55 depending on polarity of the probes) it doesn't indirectly measure plate current via the cathode like the typical 1ohm resistance method or a bias probe would. If you take out the output valves you will still measure the same thing. If you have a probe, just set it that way, or what ever your favorite bias method is. That test point was not meant for user serviceability though, as far as I remember that is.mrkrausman wrote:This amp has bias test sockets in back. It has 6l6s mounted. When I put my meter in probes it measures 55v DC not millivolts. What is happening here? Thanks in advance.