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To all who contributed to this wild goose chase: 150hz is apparently the tone created by a jfet when it's gate and source (or drain) are connected but the remaining element is not. The bit of pad connecting the trace from q1 to r23, cr1 and cr2 was missing. I had good readings across the jfets. Thanks to 52 Bill for pointing out a simple test that I should have previously completed. And to all of you for suggestions and input - thanks again.
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