I have had a problem with a couple of 475's and 475A's caused by Q904 in the A sweep circuit. This part is specified as a 151-0190-01. The base -0190 is a 2N3904, but the -01 version is a Teledyne part in a round white ceramic package with a triangular lead pattern, rather than the black plastic TO-92 of the regular 2N3904. I don't know what the selection criteria for this part are, but it is specified as being supplied by Teledyne. (There are 9 variants of the -0190 listed in Tek documentation). I have found that these tend to be lower beta than other 2N3904's, and I have had some success using the lowest-beta part I could find in this position.
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Bob Haas