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Old 7th November 2008, 02:07 AM   #1
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Default First scope/buying oscilloscope probes

Hi, I just bought my first scope!
http://cgi.ebay.com/ws/eBayISAPI.dll...m=260308554503
I know I took a slight risk on it as it's untested, but there is a return policy and all and I think I got an ok deal I feel pretty good about it. I tried to buy a popular model too so that if something is wrong I can hopefully get some support for it.
It appears that it only has one probe though, so I'd like to get another. What should I look for? I'm pretty broke. Are the 20 dollar probes on eBay bad? What should I look for spec wise? I'm not quite sure how to go since I'm new to scopes.

Cheers and thanks!
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Old 7th November 2008, 02:40 AM   #2
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i Would recommend to you that at least see some pic of the Osciloscope turn it On. you need to see at least the the Osc Turn it On,
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Old 7th November 2008, 02:44 AM   #3
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Yeah, I know that is better to see that it works...but I feel like I saved some money by taking this risk. There is the return policy too, which is pretty good. The seller looks reputable, so I trust that it turns on. If there are some small flaws with it though I think I'll probably try and fix it myself.

Cheers
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Old 7th November 2008, 03:08 AM   #4
CBS240 is offline CBS240  United States
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If it is used equipment, there is a possibility that it may need re-calibrated. But then there is a possibility that it doesn't work at all......e-bay I hope that isn't the case. Buying used equipment is a great way to save money.

Does anyone have a working used spectrum analyzer they wouldn't mind parting with?
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Old 7th November 2008, 03:48 AM   #5
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Ahhh!
I'm kicking myself in the face right now for not doing the buy it now on this guy:
http://cgi.ebay.com/Tektronix-Model-...arms=72%3A1419|66%3A3|65%3A12|39%3A1|240%3A1318
Guaranteed working for 10 bucks more. Oh well, that's how life is.

Wish me luck!
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Old 7th November 2008, 05:03 AM   #6
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Default Re: First scope/buying oscilloscope probes

Quote:
Originally posted by rockgardenlove

It appears that it only has one probe though, so I'd like to get another. What should I look for? I'm pretty broke. Are the 20 dollar probes on eBay bad? What should I look for spec wise? I'm not quite sure how to go since I'm new to scopes.
The original probes supplied with the 2235 were Tek P6109's. However a P6121 or P6122 will also match up. And I've used the older modular Tek P6105 probes also. The input is 1 megohm w/20pF capacitance. A 1 megohm input is very standard and most aftermarket probes will work with this input.

These probes are all 10X type. Meaning they reduce the signal by a factor of 10 to provide low circuit loading and maintain good bandwidth up to 100mhz, which is the 3dB point of the scope. (50% down) For all but the most critical pulse analysis, low cost aftermarket probes will be ok. They will work but may lack the durability of Tek probes.

All 10X probes must be compensated (adjusted) to the scope's input by looking at the scope's square wave calibrator output and adjusting for a sharp corner without overshoot or undershoot. This is usually done with a small screwdriver adjustment at the probe's input connector, or sometimes by turning the probe's body.

I think the 2235 has tiny lights behind the dial skirt that indicate whether a 10X probe is in use or not. This is activated by a small contact pin on the probe connector. So be sure that your probe has this feature if needed.

You might also want to buy a dual function 1X and 10X probe. These are switchable and still pretty cheap as aftremarket items. These will give you the best of both worlds. Full sensitivity at reduced bandwidth (1X) plus light loading and full bandwidth with reduced sensitivity (10X).

Victor
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Old 7th November 2008, 05:48 AM   #7
Colt45 is offline Colt45  Serbia
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I've got a 2235 too

for audio work.. and hell, a lot of RF work, $15 generic 60MHz probes are fine.
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Old 7th November 2008, 06:25 AM   #8
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I bought some 100 MHz probes on eBay; I'm sure they're made in China. I bought from two different vendors.

I connected them to the 500 MHz Agilent scope at work, and measured the rise time and bandwidth capabilities. The rise time was about 1 nS at the probe tip (that's without the ground clip; the ground connection was made directly to the sleeve adjacent to the tip). On the 100 MHz Agilent scope, the rise time was 1.9 nS.

These probes have selectable 1X and 10X attenuation; the build quality is good. Their bandwidth is more like 200+ MHz, rather than 100 MHz. They cost about $22 for two probes.

Of the two vendors I bought from, this seemed to be the best quality probe:

http://cgi.ebay.com/Two-New-100MHz-O...1%7C240%3A1318
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Old 7th November 2008, 02:19 PM   #9
roggom is offline roggom  United States
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Since you are in OR you can pick a set up at Fry's for around $30. I would just pick up a used set on CL or the bay.
Since you posted this on the Tube thread, you might want to read up on floating your scope (ground). High voltage and probes can get nasty sometimes.

I have an old 2232 Tek and it still works like a charm.
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Old 7th November 2008, 02:59 PM   #10
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Thanks for the pointer on those probes! I don't live near Fry's
anymore and I think it actually was easier to find things in Fry's
than on Ebay ;-)

I find myself needing X1 probes more than the X10, which is all
I have right now. The x10s don't let me measure low level
signals and noise.

I think it's worth taking a chance on a scope over ebay. I have
bought at both surplus places and ebay and these days I think
the ebay sellers are getting more of the good surplus. Try to
find a seller with a lot of similar gear with good feedback who
offers returns and at least claims to have checked them out.

Try to determine if the gear came from a liquidation or wholesale
upgrade. This gear is usually 99% in working order with recent
calibration. (calibration is probably not needed for DIY audio use
except for probe comp.) Companies and schools will go through
replacing many units at once and sell the old stuff, still working,
by the pound.

I think scopes are one item which you can learn a lot from the
appearance of the front panel.

And yes, the seller I bought from displayed the unit running
with a cal trace on the display.

Cheers,

Michael

PS Have fun with the new scope! I see you picked it up.

If the above suggestion is to float the entire chassis of the
scope to HV using an isolation transformer, I can't recommend
that practice. It's better to use a small transformer and a cap
to isolate just the signal if possible. Stay safe.
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