Quality equipment?

Discussion in 'General Electronics Chat' started by Armagguedes, Jan 2, 2008.

  1. Armagguedes

    Thread Starter Member

    Feb 17, 2007
    21
    0
    Hello there.

    I've been fiddling with electronics on and off for a while now, and this Xmas i got a Fluke 179 multimeter as a present (probably a bit excessive at the moment). Since i have been looking into replacing my cheesy/unbranded PSU (1x0-30V@3A; 1x5V@500mA; 1x12V@500mA) with something decent, i might as well look into it now. The problem is that i have no idea which brands to look at. [Also, a bit more on PSU specs would be nice; #outputs, ranges and current, etc.]

    I know that "B&K Precision" has some pretty good hardware, but that's about it. I have seen PSU's from "GW Instek" and "Thurlby Thandar", and 'scopes from HP. I have also heard of Tektronics (or wtv).

    Also, can you guys tell me about oscilloscopes and function generators, i would appreciate, since i have to look into those pretty soon.

    If you guys just give me some suggestions, i'll worry about financing.

    Thanks guys.
    Cheers
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Don't spend a lot on test equipment unless you're going to be making money with it immediately.

    Your power supply doesn't have to be the greatest in the world to build good stuff. You could use some more power though. Make yourself a beefy bench supply from a salvaged ATX-form factor PC supply for about $20:
    http://www.google.com/search?hl=en&q=ATX+lab+supply

    After that, consider building a multifunction signal generator from a few op amps and discrete components.

    You'll be learning as you're building - and once you get things working, you'll be able to fix them yourself.

    You can spend a fortune on test equipment, only to have it be obsolete a year or two down the road.
     
  3. Armagguedes

    Thread Starter Member

    Feb 17, 2007
    21
    0
    I suppose you are right, but i'm only posting this thread 'cos i doubt about the reliability of stuff made at home, especially given my reduced experience. The advantage of having commercial instruments is that you can at least cross-check your projects.

    Also, the notion of obsolete with this kind of gear is kinda relative, since i have seen 2 shops with very old gear (~10y?) and they were running perfectly fine.

    Btw, i do this for hobbies (at least so far) so i have no intention of making money from them, and when it comes to prices i always look around surplus/2nd hand stores.
     
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Stay far the hell away from B&K's scopes, I'm not partial to much else they have. We got one of there scopes in the late 90s. It had a trace that looked like it was drawn with a crayon. It was so thick you couldn't make out the waveform. They refused to make it right. We ended up dumping it at a slight loss and picked up a used Tektronics that had a trace you could cut yourself on. BOTH scopes had the same specs. If you get one for free of course take it. :)
    I'd recommend a Tenma anything over a B&K or Russian surplus. :) The B&K would make a good bench clock, though blurry.

    Agree about keeping test equipment purchases to a minimum. Do your damnedest to get access to good stuff.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I bought a couple of 60MHz dual trace O'scopes at a popular online auction site. One is a Hitachi V-660, the other is a Tektronix 2215. Shipping is expensive for items like those; they have to use big boxes and lots of foam. Both of them had problems when they arrived; the Hitachi has a scope bloom on the bottom left (a sign of a damaged grid) and the Tektronix a dead channel B.

    Since they're older, it was easy to find the schematics and cal specs online, and common parts are available everywhere.

    For late model stuff, you'd have to pay through the nose to get it fixed since most of it is digital and the manufacturers won't release schematics; and once it's repaired it has to be re-calibrated and the manufacturer also has proprietary calibration software that you have to either pay them a princely sum for the annual calibration or a king's ransom for the software to do it yourself.

    With the new digital stuff, they have you coming and going.

    Older test equipment generally works fairly well - but to make it last, one of the first things you have to do is replace ALL of the electrolytic capacitors with new high-quality caps. Otherwise when they DO go, you can wind up with a lot of other parts getting destroyed.

    Don't expect used equipment to be perfect. If it were, they wouldn't have taken it out of service.
     
  6. eeboy

    Active Member

    Sep 27, 2007
    90
    1
    A current limited (adjustable) supply has saved my arse many times. This should be a high priority on the feature list for a new power supply.

    I have a GW Instek dual supply (GPC-1850D). It works like a champ.
     
  7. Armagguedes

    Thread Starter Member

    Feb 17, 2007
    21
    0
    Alright, so i'm gonna get a PSU, and these are the ones i am looking into:

    http://www.rapidonline.com/producti...Us&tier4=Multi+channel+DC+PSUs&moduleno=74715

    http://www.rapidonline.com/producti...able++output+PSU+with+fixed+5V&moduleno=62152

    Do i go for the 1x5V@3A output PSU's or the one with 1x2.2-5.2V@1A and 1x8-15V@1A? I know that IC's use a Vcc of 5V, but what about current? And isn't 12V supposed to be used with motors/robotics?
    When it comes to their fixed outputs, they all have the same specifications, and only seem to vary in their looks/display or in the case of the GPS4303S, their CH3 and CH4 specs.

    What do you guys think?


    Thanks;
    Bruno
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, TTL IC's require 4.75V to 5.25V in order to function properly. CMOS has a much broader range; typcally from 3V to 15V (your mileage may vary; always check your datasheets.)

    With my converted ATX power supply, I have 18A @ 3.3V (that I won't use much) 21A @ 5V (very convenient) 8A @12V (also quite convenient) and -12V and -5V @ 0.8A (well, at least I have them.) I can also get +7V by using +5V as a virtual ground, and +12V as Vcc. If I needed more voltages, I could always use a Vreg IC such as an LM317 to get 1.2V to 11.3V variable from the 12V output, or at a lower current using the +12 and -12 outputs, anywhere between 1.2V and 22.3V @ 0.8A.

    I have several power supplies kicking around that I either picked up at salvage prices, or modified from old computers. For higher DC output, I have a Lambda supply I picked up that puts out 3A @ 0.25V-54V. I modified the regulator circuit using a 10-turn knobpot for adjustment, it has a dial indicator like a clock, and actual regulated output is within 0.2v of the dial's indicator.

    You can find deals on such things. There's no need to spend lots of money on them, unless you have a specific need.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I've had excellent luck buying used equipment from gigantic companies. For example: Boing runs their own surplus store a three hour drive north of me. Their garbage is my gold.

    Surely there are some local campuses of gigantic companies in your vicinity. Find out how they recycle their "garbage."
     
  10. Armagguedes

    Thread Starter Member

    Feb 17, 2007
    21
    0
    Regarding "local campuses of gigantic companies in your vicinity", i'm in the middle of fawking Cornwall (SW England). As far as i know only the Uni campus might scrap stuff like that. At any rate, i'll have to ask around.

    Ok thanks for your input guys.
    Cheers
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Nothing in Plymouth or Exter? Bristol perhaps?
     
  12. FredM

    Senior Member

    Dec 27, 2005
    124
    1
    What you go for should be decided by your likely requirements.. If you are into mainly low power analogue / audio, you probably need a linear supply with a voltage range to 30V, but not need more than 3A.. If you are looking at motors / robotics etc, you probably need more than 3A, and a switched mode supply is probably ok.

    Other factors: Having settable current limit on the output/s is (in my opinion) essential.. Beware - Most supplies which have an independant 5V output do not have adjustable current limit on this output -
    Having seperate switches to enable / disable the outputs is also almost essential - it is a pain to be forced to disconnect leads while setting the output voltage!

    I have an old Farnell LT30 (linear dual 0-30V, 1A) supply which has been used without problems for more than 10 years (bought second hand), and a second hand Farnell B30/20 linear 0-30V 20A block which has also been reliable + used for >10 years (used for heavier work), and a low cost switch mode BSI BSD30/5C 30V/5A + 5V/1A bought a year ago www.jprelec.co.uk for £79, which is a nice cheap useful PSU.. I would buy 2 of these if I did not have my LT30.
     
  13. FredM

    Senior Member

    Dec 27, 2005
    124
    1
    Cooke International is where I have bought most of my 2nd hand gear from, and it has saved me thousands of pounds.. Biggest savings are made if you go for items with minor faults, and fix these yourself (they do not bother to do repairs - so trivial faults, like a scratchy pot, can reduce their asking price from say £85 to as low as £15) - and they are U.K. based, so you can visit + check stuff out (not close to Cornwall though:().. They sell on-line and have an ebay shop (hope it is ok to mention this..)
     
  14. Armagguedes

    Thread Starter Member

    Feb 17, 2007
    21
    0
    I'm in Penryn/Falmouth, attending the Camborne School of Mines. I pretty much doubt these guys are going to scrap any test equipment (do they even have any?). Exeter, Plymouth or Bristol are all too far away thou...

    This is shite.
    Cheers
     
Loading...