HP 35665A Dynamic Signal Analyzer

A dynamic signal analyzer is an outstanding tool for characterizing and analyzing audio-frequency circuits. I was lucky enough to score a Hewlett Packard 35665A for a good price. It needed some love and attention to get it back in business, but I think we're there and it's been doing good work for me so far.

My first order of business was to get new feet. Apparently it's a thing that used HP gear almost always comes missing some or all of the feet. Luckily, the feet are mostly standard and are available on eBay from a number of sellers.

The other thing about used test gear in general is that it usually doesn't come with documentation. HP in particular has great documentation, but I didn't get any of it with my DSA. I've been working to catalog and accumlate all of the documentation for this beast. What I've got so far is listed farther down the page.

This instrument can save data and settings to an internal battery-backed memory. The battery was old but still working when I got it. The battery also keeps the real-time clock chip running. I was happy to find that the RTC seems to accept years after 2000, though I think maybe it doesn't automatically advance the year if it's out of a certain range? Anyway, the battery was pretty old so I replaced it with a new TL-5104 from DigiKey. The replacement was easy: totally drop-in, no modifications required.

If you've got the instrument open anyway, you might check in with GLK Instruments. They do an options upgrade for this instrument and have accessories and parts for other gear as well. They seem like nice folks to deal with.

Aside from the interal RAM disk, the 35665A can also save to 3½-inch floppy disks. I don't think you'll find these at your local office supply store anymore, but plenty of folks are selling them on eBay. Mine seems to work fine with both double-density (720kB) and high-density (the classic 1.44MB). Make sure to pick up some labels and felt-tip pens for the full retro experience.

Speaking of the retro experience, you can get a ThinkJet 2225A (the A is important; you want the HP-IB interface model) printer. This is the original thermal inkjet from HP. The story behind it is really interesting and is told in the May 1985 issue of the Hewlett Packard Journal. It seems like you can still get the cartridges new from Staples. I picked up a few new new-old-stock from eBay. They were still in good shape. They came sealed in metal tins! They include a little blotter that you replace along with the cartridge. The printer uses it to soak up ink used in cleaning the heads. The printer can feed single sheets or tractor-feed paper. Of course you'll want some tractor-feed for the full experience. You'll need an HP-IB cable too, one of the ones with black screws (the silver-screw ones have a different thread; I think they're less common). I haven't found a manual for this printer yet. If you know where I can get one, please let me know. I did find a Quick Reference that helped me out. The buttons on mine were worn off, so the little diagram and explanation of what they do was helpful. I've heard that some folks have trouble with the ribbon cable that connects to the cartridge. I guess the ink can leak down there and is corrosive enough to cause trouble even though the connectors are gold plated. Mine did have some dried-on ink that kept it from working right at first, but I was lucky enough to be able to clean it off with some 90% isopropanol and gentle scrubbing with a cotton swab.

Update: Stray Electron from the EEVblog forums dropped me a note to say that you're likely better off soaking the contacts in alcohol if they're gunked up rather than scrubbing. Apparently if the ink has had enough time to work on the plating, you can pop the contacts right off if you're not careful. He suggested that you may wish to store the ink cartridge contacts-up in an airtight container (a large pill bottle, for example) when not in use. He also mentioned that a potentially more reliable printer might be the HP 2671G thermal printer; some 2671's are text-only and they offered them with different interfaces, so make sure to get the graphics model with HP-IB interface.

If you're going to be saving a lot of files or titling prints, a keyboard is handy to have. Most any AT-style keyboard or PS/2-style keyboard with an adapter should work. I was able to get a new-old-stock HP (of course!) PS/2 keyboard from Amazon along with the necessary adapter. I did find one reduced-size AT keyboard that didn't work at all with the DSA. I'm not sure if it was a problem with the keyboard or if it was some weird compatibility issue.

Documentation

I've been working on collecting all of the documentation for my Hewlett Packard 35665A dynamic signal analyzer. I've listed below all of the documents I know about along with a description. I've included the document itself as well, where I can. In some cases, I was able to find scans on the Internet. In other cases, I was able to get a physical copy of the document to scan it.

HP 35665A Installation and Verification Guide
Part number 35665-90029
Describes how to install the instrument and perform operational and performance verification tests. The tests are very extensive and require additional instruments and tools.
I found a scan of this document on the Internet. I checked that all of the pages appear to be present and tidied it up for printing.
HP 35665A Quick Start Guide
Part number 35665-90035
Introduces the controls of the instrument and walks through some example tasks to get the user comfortable making measurements.
I found a scan of this document on the Internet. I checked that all of the pages appear to be present. It looks like it should already be good for printing.
HP 35665A Concepts Guide
Part number 35665-90028
Provides a conceptual overview of the instrument and its features. This is the main document to read for learning how to use the instrument. Going through the Quick Start first gives a good foundation. You might want to mix in some exercises from the Operator's Guide as you go along too.
I found a scan of this document on the Internet and I was also able to source a physical copy. The scan was missing a couple of pages and had some other pages jumbled up. I added the missing pages from my physical copy and unjumbled the other pages and tidied it up for printing.
HP 35665A Operator's Guide
Part number 35665-90026
Walks you through a variety of example tasks with the instrument, demonstrating its principle functions and how to use them.
I found a scan of this document on the Internet. I checked that all of the pages appear to be present and tidied it up for printing.
HP 35665A Operator's Reference
Part number 35665-90050
This document provides an encyclopedic reference organized by button, connector, or menu item. This one is good if you've already gone through the Quick Start, Concepts, and Operator's Guide and just want a refresher on a specific topic. In some cases, those documents also refer to this one for additional details about a specific topic. Much of what is in this document is also covered in the instrument's built-in help function.
I found a scan of this document on the Internet. I checked that all of the pages appear to be present.
Using HP Instrument BASIC with the HP 35665A
Part number 35665-90052
This document covers the practicalities of how to write, debug, save, recall, and run programs on the 35665A as well as some language features peculiar to the instrument. It does not cover much about the language itself.
I was able to source a physical copy of this document and scan it. My copy came with SDF Utilities (LIF and Conversion Utilities) Revision B.00.02 disk 1 and disk 2 as well as Example Programs.
HP Instrument BASIC User's Handbook
Part number E2083-90000
Has three sections: general Instrument BASIC programming techniques (kind of a language guide type document), interfacing techniques (another guide type document, but with a focus on HP-IB and serial I/O), and a language reference.
I was able to source a physical copy of this document and scan it.
HP-IB Programming with the HP 35665A
Part number 35665-90030
Provides introductory information about HP-IB and SCPI, details about programming for the HP-IB bus, and an encyclopedic reference of all the commands supported by the instrument.
I found a scan of this document on the Internet. I checked that the pages all seem to be present, unjumbled some of the pages and tidied it up for printing. I actually found two scans and this is the newer of the two documents; it looks like they re-arranged the introduction and broke out some of the information about SCPI into its own chapter.
HP 35665A HP-IB Commands: Quick Reference
I'd be interested in having a copy of this document. If you can point me in the right direction, please drop me a line.
HP 35665A Service Guide
I'm actively seeking a copy of this document, electronic or digital. If you can point me in the right direction, please drop me a line.
Standard Data Format Utilities User's Guide
Part number 5960-5759
Documents a set of PC utilities for working with SDF files as well as a technical description of the SDF file format. The 35665A saves measurement data in this format.
I found a scan of this document on the Internet. I checked that all of the pages appear to be present. It looks like it should already be good for printing.

I hope you find this page helpful. If you have any questions or comments, please drop me a line. If this is the kind of thing you're into, you might enjoy our other work.

Aaron D. Parks
Parks Digital LLC
4784 Pine Hill Drive, Potterville, Michigan
support@parksdigital.com