Cheap or free test equipment - Page 1
Forum section: electronics / general

author: johnboxall
author_rank: Unknown
timestamp: June 22, 2010, 10:26:17 am
content: After listening to David's stream of consciousness about getting an analogue oscilloscope, I thought "Yes, analogue will be fine" and started hunting eBay etc., for a used one. Then it occured to me to email the EE department at my university and ask them for any clues. By surprise they wrote back saying come over to the stores office with a couple of bags.The lab tech had stacked up a nice benchtop DMM, 1Mhz function generator and a dual-channel 20MHz oscilloscope, calibrated last year. All for free!The gear certainly isn't new, but worked perfectly, we play.. checked them for a while before sending me on my way. No probes, but a quick trip to DSE sorted that.The unversity had gone digital, and had a room full of CROs and so on. So if you're looking for a CRO that has been looked after and maintained, and you're enrolled at uni/college, hit up the electrical engineering department politely. You never know your luck!http://flic.kr/p/8cpBU9

author: dmlandrum
author_rank: Regular Contributor
timestamp: June 22, 2010, 10:48:50 am
content: I don't know where you are, but here in the States, public universities and 2-year (community) colleges are required to put surplus and outdated items up for auction, and it can be difficult to find out when and where these auctions are. Private colleges probably don't have to follow this regulation. Trust me, I've tried.

author: johnboxall
author_rank: Unknown
timestamp: June 22, 2010, 11:34:44 am
content: Brisbane, Australia. Public universities can generally write things off once their 'useful life' has ended if the value is under a set amount (this varies). At that point it is the general 'unwritten' rule that the written-off items can be given away to students, donated to student clubs, etc. For example, my uni turns over computers every 3 years, at which point they are refurbished and handed out to lower-income students.

author: Zero999
author_rank: Super Contributor
timestamp: June 22, 2010, 11:52:24 am
content: The college I used to go to had really old test equipment, some over 20 years old.I have two analogue 'scopes, an old Cossor 75MHz which I bought cheaply off a colleague and a 10MHz Tectronix which someone gave me for free. I had an old 16MHx Gould 'scope but it was temperamental so, rather than spending the time to fix it, I gave it away.

author: Unknown
author_rank: Unknown
timestamp: June 22, 2010, 12:57:57 pm
content: 20 years old isn't that old for test equipment, unless you're comparing to the current high-end stuff. In 1990, there were decent digital oscilloscopes, analog scopes to 1GHz, multimeters to 8.5 digit (the current HP 3458A was introduced in 1988 or so) and good signal generators (though not that much DDS stuff). The majority of my test equipment is over twenty years old (all bought used). Most of the test equipment hasn't improved that much compared to 1990, except for fancy displays and more digital control. It's more a matter of the market segment (cheap junk from 1990 is now even cheaper junk) than age.

author: Zero999
author_rank: Super Contributor
timestamp: June 22, 2010, 02:03:03 pm
content: Quote from: alm on June 22, 2010, 12:57:57 pmI left college back in 2006 so that would've been 1986.Anyway, all the equipment you've described would've been really expensive back in 1990.All the equipment at college was all probably second hand when the college acquired it and hadn't been calibrated for many years.

author: saturation
author_rank: Super Contributor
timestamp: June 22, 2010, 02:44:30 pm
content: Many US private schools give away depreciated gear, far cheaper than to repair them.I once donated 50 PCs to a church, the paperwork to do so was horrendous, even if it was free. It was easier to label it trash, dump it into a clean dumpster, and tell the charity to go there and pick it up. The church told me the kids cannibalized the PCs and got 20 working well.Since PCs and other electronics are now considered a type of hazardous waste, the paperwork is even worse and now they cannot simply be trashed.Quote from: tronixstuff on June 22, 2010, 11:34:44 am

author: Unknown
author_rank: Unknown
timestamp: June 22, 2010, 03:00:24 pm
content: Yep, I mentioned some high-end equipment from the eighties, hence my point that the fact that it was high end or cheap junk is more important than age. Many of the old high-end stuff is better than current low-end stuff. There are some examples were newer technology has made it possible for cheap equipment to surpass old high-end stuff, eg. anything related to computers, but in many cases not. General test equipment has been quite mature and usable for many years, so unless you need something specific like a protocol analyzer for a modern protocol, old stuff is often just as good. For example, what was improved to multimeters in the last 20-25 years? When comparing similar market segments, accuracy has improved, speed has improved (for system DMM's), storage and math features have improved, extra features like capacitance tests have appeared and some shiny stuff like wireless (Fluke 233) or trend graph (Fluke 289). But the old stuff was quite good for the essential voltage/resistance/current stuff. If you compare them at the current market prices, you can probably get a mid-end 5.5 digit bench meter (equivalent model today costs $700 or so) for $100, or a mid-end 3.5 digit hand-held DMM. You can argue about bench vs. hand-held and a few good functions vs. jack of all trades that will do capacitors, inductors, transistors and capacitance, but it's hard to claim that the $100 Extech/Amprobe is clearly superior to that Fluke/HP/Keithley meter. Same for a $400 Rigol scope vs. a $400 Tektronix 7000 system or 24xx analog scope. The Rigol is digital and has more automated measurements and storage, but the analog scopes have more bandwidth and more features (eg. triggering), and a much faster update rate.Improvements have mainly been large LCD displays, USB control, buttons instead of knobs (although you can argue if this is an improvement). Of course performance on the top-end has been improved, but the current top-end is rarely an option on a hobby budget.I've seen plenty of (high quality) equipment that wasn't calibrated for many years still meet its factory specs.

author: KTP
author_rank: Frequent Contributor
timestamp: June 22, 2010, 11:16:45 pm
content: Quote from: alm on June 22, 2010, 12:57:57 pmI got a couple pcs of 20 year old equipment last year (A Tek 495P and a 7104 1 Ghz mainframe with a bunch of plugins) for a few hundred bucks but haven't had a chance to do anything with them except a powerup to see if they worked. I am not really sure they are worth $200, but I bet they were quite a bit more than that in the early 1990s.

author: Unknown
author_rank: Unknown
timestamp: June 23, 2010, 04:37:12 am
content: Quote from: KTP on June 22, 2010, 11:16:45 pmIf they work, it's probably worth quite a bit more than that. A 7104 alone is worth a few hundred dollar in good condition, a 495P probably more (never looked for one, but spectrum analyzers are always more expensive than scopes). The 7104 is the fastest analog scope ever made (bandwidth to 1GHz, although only with the direct access plugin), and was sold for about $27k in 1989. Take care not to burn that CRT if it works, MCP CRT's are kinda delicate. The switching power supplies seems to be hard to fix, parts availability appears pretty good, even most custom IC's (fair number in common with other scopes, plus it's quite popular). Plugins depend on the popularity and performance from $10 to over $200 each. But that's all in working condition. When non-working, it depends on the feasibility and expense of the repair. I usually value broken equipment quite low unless I'm confident about the problem and that I can fix it and get the parts, because if I can't, I'm stuck with a paperweight, unless I can unload it to someone else (but I'd mention the defect and that I failed to repair it, which would lower the price). Even in parts condition, $200 is probably below market price.

author: KTP
author_rank: Frequent Contributor
timestamp: June 23, 2010, 05:32:44 am
content: Quote from: alm on June 23, 2010, 04:37:12 amThe 7104 came with three 7A29 plugins and a 7B10 timebase. It seems to work perfectly, and no CRT burnin, but I don't have anything anywhere close to fast enough to test it with. And it is friggen huge! I wonder how long this type of equipment will keep working though before the capacitors dry out?

author: Unknown
author_rank: Unknown
timestamp: June 23, 2010, 05:55:30 am
content: Plenty of other stuff from the sixties and seventies is still working with its original capacitors, but on the other hand those were mostly linear supplies, so ESR was less critical. It would be an easy fix, so I wouldn't worry about it.Those are the standard plugins, though I think you need the 7B15 in addition to the 7B10 for delayed timebase. The vertical plugins are 50ohms, so only work with FET probes (I think the mainframe has the power connectors), lo-Z probes or standard 50 ohm cables (if your source is 50 ohms). There are also 1Mohm plugins, like the 7A26. These will work fine in the 7104, but have only 200MHz bandwidth. They will allow you to use standard hi-Z passive probes. There are also other plugins like spectrum analyzers (probably not that useful if you have a 495P) and curve tracers, but they are rare and expensive. Other interesting plugins are the 7A13 and 7A22 (differential, the former does up to 100MHz and has a comparator for large DC offsets, the latter is only 1MHz, but goes down to 10uV/div and has a 100,000:1 CMRR). Some people will think it's a waste to use such a special scope for low bandwidth applications, prompting you to buy yet another mainframe. But that's if you want to get into the whole 7000 craze, it's easy for me to avoid, I don't have the space.Apologies for the off-topic posts, although it is a good illustration that there's some great equipment from over twenty years ago.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 23, 2010, 11:13:54 pm
content: A major improvement of modern gear is size - if you have the luxury of having plenty of space, you can kit out a workshop with good gear for peanuts.I bet there are still a few old Tek 547 valve hernia-scopes (about 500w power draw ISTR) running somewhere, and stuff like Tek 2465s and 465s are still perfectly useable analogue scopes.

author: saturation
author_rank: Super Contributor
timestamp: June 23, 2010, 11:37:23 pm
content: I'd think too and power consumption and weight. When I look inside old gear, I think the durability of parts way past their rated life is a testament to the quality of their component construction and design, and any derating often given to choosing components. Time has proven just how well made they truly are.Quote from: mikeselectricstuff on June 23, 2010, 11:13:54 pmQuote from: alm on June 23, 2010, 05:55:30 am