By accident, a couple of years ago my eMail address was shown in the archives as having a PDF copy of the HP 8590 manual. I DO NOT have such a manual, yet I receive periodic requests to forward a copy of it!
If you need information on older models of HP test equipment, they have some of it on their web site. The HP/Agilent web site is in the process of being revised, so this information may not be true in the future. When that happens, you may be able to use their search function to find any information they have for your equipment. This information was correct as of 11/24/2005.
Go to the HP/Agilent web site at
Under Test & Measurement Equipment, select Repair and Calibration Services.
Under Key Library Information, select Manuals & Guides.
In the search box, enter your model number, choose Test & Measurement Equipment and click on Go. (You might also try the other options.)
When I entered 8590, there were 25 entries available, including several .PDF files for download.
Fred