Sphere BC in California have a list of HP semiconductor cross references
https://www.sphere.bc.ca/download/hp_xref-free.pdf
Thanks Kevin, that's going to be a valuable resource. I had found this one bulletin
http://hparchive.com/Bench_Briefs/HP-Bench-Briefs-1987-10-12.pdf.. while trying to decode a opamp on the same board.
David, those are abbreviated HP part numbers. Look for 1854-0457 and 1854-0636.
Precaud, I'm wondering how did you arrive at "1854" for the first four digits?
If I just search Kevins document for "0636" I get.
1826-0636 03285 AD7525KN - X Analog Devices 18pin DIP
1853-0636 03334 2SA812 - X Philips SOT-23 PNP
1855-0636 00039 NE71084-06 - NEC weird package FET.
Search for "0457" I find.
1853-0457 02037 2N5400 - TO-92 PNP
1901-0457 02062 QSRD-4652 - ??
1826-0457 03406 LM325H - Dual opamp, 10 pin metal can
1820-0457 02910 N8162N - ??
Here is a pic...