I agree on two channels; phase angle measurement is important, and you can only do that with two channels. I would add that for a first scope, you might want to consider an analog, for two reasons:

They are less in demand = you can get one for less dollars, usually.

They will force you to learn how to use the cursors, rather than just read out the values from the Measure Menu. The Math Menu can also make one lazy. If you can use an analog scope, you will have no problem using a digital, but if you can use a digital, there is no guarantee you will be able to use an analog o-scope. If we are onto the car analogy, then it is like learning a stick shift first, rather than an automatic.

 

There is a good tutorial on ebay about buying an oscilloscope there.
It is writen by a guy who repairs them.
You will have to look around for it, its writen by one of the guys that bids on alot of them.

I bought a tek 465B,100MHz, off ebay and it works great.

I did alot of research before I bought it.

I only looked at ones that were claimed to be in good working order and gave a money back guarantee.

There are some great deals( and some bad ones) on ebay.
sam

 

To answer some questions and clarify a few points:
-"Dual channel" means you can hook up two probes and track two signals at once. The principle application of this is to use an enabling signal, such as /CS (chip select) on a RAM chip, to act as the trigger so you can see the relationship of the data and address lines (among others) to this central signal.
-"Dual beam" means you have two guns painting two traces on the display at the same time. This is prefered for two-signal work. Most lesser two channel 'scopes have one gun, so either display one channel, then the other; or do what's called "chopping". Chopping is where you show one signal's trace for a small period of the total sweep, switch to the other to show a small portion of that, and keep doing this switching throughout the sweep period of one full display. The problem with this is you run the chance of missing some key event because something ends up getting cut out because the chop is looking at the other signal at the time.
This is where modern digital scopes with LCDs shine. Both signal are read and digitized, then both are displayed on the LCD at the same time.
-"Digitizing" simply means the incoming signals are measured on a timed basis, as binary values, then stored in onboard RAM for later (near instant) display. The better scopes allow you to take one reading only (sort of a "freeze frame"), then study it at your leisure or download it to a computer for later, deeper analysis.

The vast majority of the scopes you find on Ebay are servicable analog scopes. These typically have two inputs, 20MHz to 100MHz, but one gun, so supply chopping controls, with all the limitations mentioned above. The early DPOs (Digital Phosphor Oscilloscopes) will give you "freeze frame" ability, but the storage is you and a camera, as the results only stay on screen for a short time. And they aren't cheap, easily more than the $150 you mentioned.

There are pros and cons to analog and digital scopes:
Analog will still do 98.5% of what you want to do in electronics work, IF you are only interested in frequencies, levels and rise/fall times. Which is what most electronic troubleshooting is about. It excels at showing minor discrepancies in a continuous signal because you see the irregular, infrequent events as dimmer signals amongst the strong, regular signals. You can catch ringing and overshoot problems easier, for instance. But they suck at catching one-shot events in the middle of a lot of traffic, or in long periods of no activity at all (seems like?). But, a modern digital scope with extended triggering capabilities will catch these rascals easily.

If you must catch infrequent events reliably, with expanded triggering capabilities, or store traces and download them to a PC, then digital is the only way to go. Even units running less then $400 will do this. I saw an ad in an email recently (search these forums, or Google, using "OWON", as I believe this has been covered here before) of a two channel scope that has 25MHz bandwidth with 100MS/s (megasamples/second, the more the better) with must-have features comparable to my $2400 Tektronix 4-channel color LCD scope. Of course the manual is Chinlish in the worst way (but usable) and isn't very informative about using the USB port, but it can download displays to a PC for printing. It has a color LCD; variable phosphor (nice!); and a limited, but usable, built-in math package. It has a measurement bar on the screen's right that allows you to track five values on-the-fly. One ad even says they throw in a free battery, which suggests portability, but I couldn't find anything about installing the battery in the manual. Beware!
Amazingly, it has more memory per channel than my Tek!

I hope this answered more then it confused.
kenjj

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kenjj,
Thanks, that was really worth reading!

 

I've got two, a GW 20MHz double beam, and an Hitachi 30MHz double beam.

At work I use a Grundig 50MHz double beam.

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Don't forget the ability to mooch or exchange services for the usage of someone else's scope on occasion - maybe someone local to you has one that you could use. I always abused my friends in my old town for woodshop usage, in exchange they got to abuse me for my electronics and computer based electroacoustic software (we were all speaker builders and stereo DIY'ers; they had a couple of grand in their woodshops, I had a couple of grand in my electronics measurement & design stuff). 'twas mutually beneficial.

 

There is not a damn person around here who even knows what the hell a resistor is; Let alone what the difference between analog and digital circuits. My school doesn't even own an o-scope! THEY DON'T EVEN OFFER AN ELECTRONICS COURSE!!!!!!!!!!!!!!! Everytime i bug the school board, they just push me away making excuses for why we cannot have an electronics course. My school is more worried about sports than they are about anything else!

I taught myself programming, now i am trying to teach myself electronics...

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Tektronix TDS210 or TDS1001B are good ones. You can buy them at around 400-600 USD on ebay.

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If you are looking at simple digital circuits, maybe a simple logic analyser. There are plenty of circuits around, interfaced to a PC so no seperate screen is required.

 

I have looked into making a simple logic analyser. IMO, they are crap...

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Haha lol. Sorry to go off-topic, but I am in your exact same boat

 

I have the inverse problem. No students. Most of them seem to lazy to do the work needed to learn to program.

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That is a problem here as well. There are only two people in my school that know how to program; my friend and my self. Same with electronics. That is 2 students out of ~400.
Oh well. It is kinda nice being the only true geeks in this area. People kinda look up to you...

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