What specs to look for in an oscilloscope? - diyAudio
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Old 8th February 2007, 01:31 AM   #1
spooney is offline spooney  United States
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Default What specs to look for in an oscilloscope?

Just like the topic says.The only reason I'd like to buy one is for audio repair. Can I get by with one that maybe doesn't have the greatest bandwidth or features?I have no idea what to look for in these things but I think its a necessity if I plan on learning more about amplifier repair.
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Old 8th February 2007, 02:03 AM   #2
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Don't worry about bandwidth. I have two scopes with 2MHz (not a typo) bandwidth and they work fine for virtually any amp made.

If you're going to buy on eBay, be careful of the scopes that are sold as-is or from buyers who say they don't have the knowledge to test them. I've seen sellers who said they didn't know how to test them but when I looked at their history, they clearly knew how to test other scopes they sold.

I'd suggest that you avoid virtually all scopes that don't show a 'locked' waveform on the display. Those with no display may not be able to produce a trace. Those without a locked waveform displayed may have triggering problems.

If the photo is taken in a darkened room, it's likely that the CRT is weak and the trace wasn't bright enough to be photographed clearly under normal room lighting.

I'd suggest Tektronix scopes. B&K also makes some good scopes. In the Tektronix line of scopes, the old 400 series scopes are a good choice. The somewhat newer 2200 series scopes are also a good choice. Stay away from the older LCD scopes and the 2400 series scopes. They have too many problems.

If you're on a really tight budget and are going to buy the cheapest scope possible, make sure it at least has a triggered sweep. If it has a trigger source selector (internal, external, ch1, ch2...), it has a triggered sweep. If the timebase simply has a frequency selector, it's not likely to have a triggered sweep.

If you can get it with probes, that may save you money but probes can be defective and older probes are more likely to be defective than a cheap set of new, generic probes.

Be very careful about shipping charges. Old scopes are heavy and shipping and 'handling' can cost more than the price of the scope. Get a firm quote on shipping before ordering.
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Old 8th February 2007, 05:03 PM   #3
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Quote:
Originally posted by Perry Babin
I'd suggest Tektronix scopes. B&K also makes some good scopes. In the Tektronix line of scopes, the old 400 series scopes are a good choice. The somewhat newer 2200 series scopes are also a good choice. Stay away from the older LCD scopes and the 2400 series scopes. They have too many problems.
The 2400 series scopes are among the best analog scopes Tektronix ever built -- and there are boatloads of them for sale all the time, but absolutely buy from a seller who deals in scopes -- someone who will take back a dud.

The 500 series are very heavy -- but also very quiet. The older TDS scopes and HP digital scopes -- well -- I am not the first to say this -- old digital scopes don't lie, but they don't always tell the truth.

The Hitachi, Phillips scopes are pretty good as well.
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Old 8th February 2007, 06:22 PM   #4
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jackinnj:
I agree that the 2400 series scopes are very desirable (I wish I had one) but they're not a good choice for someone that's just starting out.

The problem with the 2400 series scopes is that they use proprietary hybrid ICs that fail and new replacement parts are no longer available at any price. In some cases, the only way to repair a scope with a dead vertical or horizontal hybrid IC is to salvage it from another scope. The problem with that is that the hybrid IC is likely the reason it's being used as a parts scope.

If I'm not mistaken, the older TDS scopes had significant problems with leaking capacitors that made them virtually un-repairable unless the problem was caught early. Again, not something that you want to have to deal with when there are lots of other options.

The scopes I recommended are, for the most part, readily available, inexpensive, reliable and repairable.


spooney:
If you're unsure about a scope you're thinking about buying, post the link here.
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Old 9th February 2007, 06:17 PM   #5
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I picked up a Tektronixs 2445 on ebay for $255 recently cal'd . Same model that I used daily while I was active duty USAF.

cursors didn't show up very well in photo. But you get the picture. This scope is 150mhz, overkill for audio.
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