CRT Spectrum Analyzers in the audio range. (Intro and WTB 3585a) - Page 1
Forum section: electronics / testgear

author: Rhythmicons
author_rank: Newbie
timestamp: March 17, 2021, 07:26:19 pm
content: Hello,Several years ago I purchased a TEK 475 to use with Moog synthesizers. Shortly after that I became very curious about the HP3585 series spectrum analyzer. I'd like to be able to compare oscillators and filters in a way that conveys useful information as well as to introduce my son to the principles of analog subtractive synthesis.I've noticed, however, that the asking prices for these seem to have tripled in the last five years from online test equipment houses.Where do you find these for reasonable prices and where do you get them serviced? Are there any other analog analyzers with decent sized displays that might be suitable alternatives? I'm purely interested in the audio spectrum.Thanks,Eric

author: Cubdriver
author_rank: Unknown
timestamp: March 17, 2021, 08:00:57 pm
content: In addition to the 3580A, you might also keep an eye out for the HP 3582A and 3562A. Both occasionally show up for not insane $$ on everyone's favorite auction site.-Pat

author: Rhythmicons
author_rank: Newbie
timestamp: March 17, 2021, 08:37:49 pm
content: Thanks for the replies thus far.edavid,I hadn't seen the 3580a, but I'm drawn to the 3585a/b because of the way that it looks. My concerns are cost and long-term serviceability. The frequency response down to 20Hz is better and I wouldn't shy away from using it in conjunction with amateur radio equipment. I'd settle for a digital scope if that's going to be a better option, but I really want the immediacy of analogue without having to get a computer involved.The desire for hardware is often purely irrational...Cubdriver,There was an older post that I came across on this forum today that recommended shying away from the CRT units because the power supplies were impossible to rebuild. Do you agree with this? I'm assuming that some of these vintage scopes have dedicated communities of users and I'm hoping to find them.

author: Cubdriver
author_rank: Unknown
timestamp: March 17, 2021, 10:01:36 pm
content: Which power supplies were they referring to as far as them being impossible to rebuild? If they mean the actual CRT HV stuff for the CRT drive, then yes, things like flyback transformers may be difficult to source if one should fail, and the CRTs will eventually wear out, but by and large they're pretty reliable instruments (certainly those from major players like HP at least), and the main power supplies on older gear are probably EASIER to maintain than those on newer things as the new ones typically use switching supplies and they often are not documented as in many cases they're off-the-shelf assemblies purchased from an outside vendor.As for failing CRTs, in some instances (such as the 3562A at least) there are aftermarket LCDs that can be fitted (a company called Simmcon Labs makes replacements for a number of popular HP and Tektronix instruments; while I've never used one and they are not cheap they appear to be nearly plug-and-play replacements that require a minimum of effort to install.https://www.simmconnlabs.com/As far as dedicated communities of owners, you've found one here - look in the test gear section and if you want to really get sucked in to irrational collecting, go look at the TEA thread in that forum section.Additionally, there are several mailing lists dedicated to the care and feeding of old test gear -The HPAK mailing list/group:https://groups.io/g/HP-Agilent-Keysight-equipmentTek Scopes:https://groups.io/g/tekscopesTek scopes 2:https://groups.io/g/tekscopes2-Pat

author: xmo
author_rank: Regular Contributor
timestamp: March 17, 2021, 11:51:19 pm
content: You said: "... I really want the immediacy of analogue..."--------------------------------------------------------------The 3585A is actually a digital instrument. I don't think an analog audio spectrum analyzer will offer 'immediacy' in the way an analog oscilloscope does because of the time constants of the resolution filters.I had an analog Systron Donner spectrum analyzer and it was S.L.O.W. so a soundcard based solution might be something you could try.There are a number of standalone test instrument choices you could look at like the 35665A or 35670A dynamic signal analyzers.For full featured audio testing there are instruments like the Tektronix AM700, the R&S UPL and several from Audio precision. Anything with XLR connectors on the front panel gets my attention!

author: xmo
author_rank: Regular Contributor
timestamp: March 18, 2021, 12:14:48 am
content: BTW, I am a certifiable test equipment addict. Be careful. It could happen to you.So you can see what these instruments look like in use, here is a test bench configuration where I was evaluating the frequency response and other characteristics of communications headsets. There are two analyzers, the Tektronix AM700 and the R&S UPL so I could evaluate in both directions.The generator test signal from one instrument is amplified and sent to the acoustical manikin (HATS) which 'speaks' to the headset microphone which is interfaced, amplified, and returned to the instrument's analyzer side.In the other direction, the analyzer's generator is amplified, interfaced, and sent to the headset earpieces. Couplers (specialized microphones) in the HATS ears then 'hear' the test signal which is amplified and sent back to the analyzer. There are Rane programmable equalizers in each direction to compensate for HATS characteristics.

author: Rhythmicons
author_rank: Newbie
timestamp: March 18, 2021, 02:14:56 am
content: XMPI should probably should have disclosed at the onset (if it's not already apparent) that I have ZERO engineering knowledge and I can't even solder. I make youtube videos like this one which shows what wave clamping on a 921 series (in this case a Moog clone) oscillator looks like.I think that a crt-based spectrum analyzer (I presumed that was analog because of the display) would have more appeal than a sound card based app (I'm on a Mac also).If I buy an effect that has some unwanted noise. I'd like to be able to isolate exactly where that hiss, ground noise, or unwanted artifact lies. I've seen situations before where I clearly hear something and send the unit back to their reply that they weren't able to reproduce it on their bench.Am I approaching this the wrong way?Cubdriver,I couldn't find that post about the power supply to respond with more clarity regarding what that user wrote. My takeaway was to avoid all crt based units.The gentleman from the HP museum told me that he wouldn't give more than 600 for a 3585a in good working condition. Where are these units hiding? Test Equipment Depot and all of the other similar sites seem to think that 3K is more reasonable.Eric

author: graybeard
author_rank: Frequent Contributor
timestamp: March 18, 2021, 02:33:32 am
content: I would just useARTA FFT softwarewith the sound card on your computer. It works great and is free if you do not want to save the data.The $103.32 license fee for the full version is very reasonable considering it's capabilities.

author: james_s
author_rank: Super Contributor
timestamp: March 18, 2021, 02:59:08 am
content: I can't figure out why the prices on these things are so high either. I wouldn't mind having one for the cool/nostalgia factor but other than that they really don't offer anything over a modern PC based instrument.Most people who have vintage gear like this service it themselves, it's not the sort of thing non-technical people buy in the first place.