finding a cheap oscilloscope

[wing]

just a few questions... are old model oscilloscopes ok? what do you guys think of heathkit? if i find an oscilloscope missing the leads, will these be hard/expensive to replace, or can i just hit up radio shack real easy? is it ok to get an oscilloscope missing the manual (will it still be understandable)?

what and where would you suggest i look?

[jerrymac]

blue,
be on the lookout for a two input one with "dual trace" and X-Y abilities. This will keep your option open for more things. The dual trace means you can have both probes on doing different things on the screen at the same time, and X-Y lets you do both inputs on either axis so you can do the lissajous pattern for phase and azimuth.

the thing I always think about is this: I see cheap used 'scopes at flea markets and yard sales, but are they even close to calibration? Would it be better to drop the $400 on a new, budget model? I know for a while I had three nasty hand-me-downs. A single trace old Tektronix, then a single trace Heathkit, then a huge old tube powered tektronix dual trace. that thing could heat the room, and it had it's own rollaround cart. I did the best I could with them until I could afford a new one. That old tube powerd beast had a zillion tubes in it, and a huge two speed fan on the back. When it finally died (CRT just quit one day), I pulled the other tubes out and sold some of them on ebay. Some of them were the Amperex Bugle Boys.

Hope any of that helps.

jerrymac
my goodness, this is my third or fourth post today.

[jerrymac]

man, i'm tired. i meant to also add that leads should be available at rat shack, but they are carrying less and less components and stuff like this and selling just phones. There's always mail-order. New leads are cheap, if I recall, maybe $15 for a pair? Like I said, I'm really tired and I shouldn't be posting.

[soundmaniac]

I don?t really know much about o-scopes, other than how to check azimuth, but I?ve got a really old HP and it seems to work fine. I think I paid $25 for it. I asked a tech (that I took my machine to when I first got it) about them and he said that old ones are fine, just ?slow? (though I?m not quite sure what that means).

Radioshack doesn?t have probes, I?ve already tried. You?d be lucky to find someone there who even knows what an oscilloscope is.

I wouldn?t say that probes are exactly cheap, either. The best I?ve found is Parts Express who?s got them for $27 each , and I think they?re around $40 from Mouser. If anyone knows anywhere cheaper, I?d love to know ?cause I?m using a rigged one that?s missing a ground clip, and I?m too cheap to buy a new one at those prices (even though I somehow manage to pay $75 a reel for tape?hmmm).

the thing I always think about is this: I see cheap used 'scopes at flea markets and yard sales, but are they even close to calibration?

How does one re-calibrate an old scope? Is it possible for the average diy-er, or do you actually have to know what you?re doing? Like I said, mine seems to work ok but I suppose getting a new one would be good if you want to be on the safe side.

[dgochenour]

I've purchased a lot of stuff from here:

http://www.specialized.net/ecommerce/shop/frameset.htm

It's not dirt cheap, but the selection is good. It also a good site just to see what's out there and what things cost.

[jerrymac]

I don?t really know much about o-scopes, other than how to check azimuth, but I?ve got a really old HP and it seems to work fine. I think I paid $25 for it. I asked a tech (that I took my machine to when I first got it) about them and he said that old ones are fine, just ?slow? (though I?m not quite sure what that means).

I'd bet that the tech was talking about the highest frequency a scope can read. Like a 5Mhz scope is slower than a 30Mhz scope.

Radioshack doesn?t have probes, I?ve already tried. You?d be lucky to find someone there who even knows what an oscilloscope is.

I wouldn?t say that probes are exactly cheap, either. The best I?ve found is Parts Express who?s got them for $27 each , and I think they?re around $40 from Mouser. If anyone knows anywhere cheaper, I?d love to know ?cause I?m using a rigged one that?s missing a ground clip, and I?m too cheap to buy a new one at those prices (even though I somehow manage to pay $75 a reel for tape?hmmm).

I don't know where i got $15. I bought them at my local big electronic supply place a few years back. I don't even go into rad schack anymore unless I really have to. that place went from bad, to a joke.

the thing I always think about is this: I see cheap used 'scopes at flea markets and yard sales, but are they even close to calibration?

How does one re-calibrate an old scope? Is it possible for the average diy-er, or do you actually have to know what you?re doing? Like I said, mine seems to work ok but I suppose getting a new one would be good if you want to be on the safe side.

'scopes have to be calibrated back at the factory. The thing I was trying to convey in my first post was that a cheap, used scope, even out of tolerence, is probably fine. The only thing I can think of that would make problems is if the thing is drifting while it is on, giving you different readings for something that should have been the same.

jerry

[EasyGo]

If one has a machine with RCA connectors (sorry Blue), you can use a stereo RCA cable and a pair of RCA to BNC connectors from RS in place of probes. For the XLR connector folks, I'd imagine there would be a way to replace the RCA connectors with XLR connectors to make this work for pro tape machines. I'm kind of an idiot, but the above worked for me.

[biasvoltage]

Old, "slow" scopes are just fine for the audio frequency ranges you're going to be dealing with in setting up your deck, blue. I picked up an old 1mhz HP from Skycrafter's Surplus in Orlando FL for about $50 a few years back, and it's been working great. I also picked up an HP sweep oscillator from EBay a few months ago, which is really cool, because it maintains a consistent 0dbm output across it's entire frequency spectrum (1hz to 1mhz!)

You are going to want a dual trace oscilloscope, because that is how you check your azimuth. You hook one side of the scope to channel 1 of your machine, the other side up to channel 8 (the idea being, opposite physical edges of the tape), throw the scope display into X vx Y, and when playing the 15k or whatever tone it is off your MRL you should see a straight line at a 45 degree angle. You adjust the azimuth screws only if you see an ellipitcal shape.

As far as probes go, screw 'em. My scope has binding posts on it, so I've got it wired up to the patch bay directly.

People think you're really hardcore when they see a crazy looking scope in your rack.

cv

[wing]

excuse my ignorance, but what does it mean to check your azimuth? what IS azimuth?

[NewYorkDave]

I've owned something like fifty oscilloscopes, and what I've learned is that buying an old, off-brand scope of dubious calibration just isn't worth it. You need to be able to trust your test equipment, and you certainly don't want to have to waste time fixing a scope before you can use it. Just because it turns on and displays a trace, that doesn't necessarily mean it's in good working order. A scope is a very complex system and many failures can occur.

I love old tube scopes (I have a collection of Tektronix "doghouse" scopes from the '50s and '60s which are in good working order and used frequently), but I wouldn't recommend a tube scope to a beginner. They simply require more maintenance, and it's a bit more complex than cleaning pots in a mixing board, or aligning a tape machine I would recommend a later solid-state scope like the workhorse Tektronix 465 or 465b. You can find them at reasonable prices, since it was a very popular scope in its time and many were sold.

It's a myth that you don't need bandwidth for audio work. Audio devices, when they misbehave, can display symptoms way outside of the audio band, and a 1MHz scope is never going to let you see that a transistor in your preamp is oscillating at 10MHz. It does happen... Semiconductors and even tubes used in audio equipment often have usable bandwidth up into the VHF range. But you don't need the latest gigahertz-bandwidth scopes... 25, 50 or 100MHz is usually enough.

Some desirable features to look for on any scope:
Dual trace
Delayed sweep
X-Y mode
External horizontal input
Amplitude calibration output for adjusting probe compensation (which also makes a dandy square wave source for general testing if you need one).

Regarding probes: no, you can't just use any old piece of cable.. sorry guys. Well, OK, sometimes you can; but in many cases, the capacitance will affect the operation of the circuit and give you false results (or cause the circuit to misbehave, or stop misbehaving, when you probe it). Best to use a switchable X1/X10 probe with variable compensation. Pomona makes some good ones that don't cost too much.

[uqbar]

I purchased new probes (and received advice) for my old ebay procured Tek scope from Stan Griffiths. His info is on this page:
http://www.repairfaq.org/REPAIR/F_Manuals.html

I think I paid like $45 for my scope and nearly as much for probes, manuals, cleaning supplies, etc...

mark

[aurelialuz]

what is external horizontal input good for?

alex

[I'm Painting Again]

hey blue is it an option to rent a good scope for a day to do your thing?

[wing]

hey blue is it an option to rent a good scope for a day to do your thing?

i dunno... where do i go for that? while i'm at it, can i rent an MRL tape for a day? eventually i'll want to get all this stuff, but i'd like to get it up and running ASAP instead of waiting around to get all this stuff, which may be another month or two.