Should I buy a cheap oscilloscope?

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Should I buy a cheap oscilloscope?

Postby modman » 27 Aug 2008, 00:17

There are so many of them on Ebay for <100EUR...

What resolution should it have to be useful? Channels? If I understand it correctly, I could tune and debug circuits without having to turn on an amp and wake up the kids at night?
Or better try a free software based oscilloscope?

Or do I need a very good understanding of electronics to be able to use it properly?
thanks!
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 27 Aug 2008, 00:47

modman wrote:There are so many of them on Ebay for <100EUR...
What resolution should it have to be useful?

20 Mhz should be enough to see even HF-oscillation (even 5 Mhz to 10 Mhz will do it for audio applications)
modman wrote: Channels?

one is enough, two are better.
modman wrote:If I understand it correctly, I could tune and debug circuits without having to turn on an amp and wake up the kids at night?

If you don´t tune and debug an amp you don´t need to turn it on. If you tune and debug an amp you have to use an load resistor. A cheap 8 Ohm/50W load resistor can be made with 6 pcs. 47 Ohm/9Watt resistors in parallel (for 8 Ohm/100W use 12 pcs. 100 Ohm in parallel). If you make two of them you can connect them in series for 16 Ohm or in parallel to achieve 4 Ohm.
modman wrote:Or better try a free software based oscilloscope?

The resolution of soundcard based are not satisfying me.
If you find an acceptable one, please let me know.
modman wrote:Or do I need a very good understanding of electronics to be able to use it properly?
thanks!

The oscilloscope ? Not really....
The software ? maybe.... depends on the programmer :twisted:

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Re: Should I buy a cheap oscilloscope?

Postby marshmellow » 27 Aug 2008, 14:42

The problem with software based oscilloscopes is the voltage input level. If you work on a tube amp you might heavily overload (destroy?) your line input on the soundcard. Of course you could work with a voltage divider in front but it isn't the nicest solution to me.
If it's only for effects building there should be no problems with the soundcard osci.

I would look for an older Hameg one (at least I like working with those) with the specifications Analogguru posted. They are on Ebay all the time and well within that price range.
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Re: Should I buy a cheap oscilloscope?

Postby modman » 27 Aug 2008, 21:10

Thanks for specs.
I wasn't really thinking about "using on oscilloscope to test an amp" but rather "turning on an amp to connect a effect circuit to it in order to debug it with the audio probe."

Isn't this the only way to know what a circuit is really doing?
Would it help me repair complexer circuits like Digital Delays and an EH microsynth?
My Screamer works perfectly but sounds terrible - a scope would help me to pinpoint what that otherwise undescribeable "bad sound" is and where it comes from. Right?

It seems I should be able to find one under 50 EUR even.
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 27 Aug 2008, 21:37

Would it help me repair complexer circuits like Digital Delays and an EH microsynth?

yes.....BTW, do you have a microsynth ?
It seems I should be able to find one under 50 EUR even.

What are you waiting for ?

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Re: Should I buy a cheap oscilloscope?

Postby modman » 27 Aug 2008, 23:39

analogguru wrote:
Would it help me repair complexer circuits like Digital Delays and an EH microsynth?


yes.....BTW, do you have a microsynth ?


Yes. It's not mine, but belongs to a friend. It had volume issues and was not true bypass and a real tone sucker. Just wanted to install a true bypass, but there is nothing coming from the circuit anymore. Audio probing that is not so much fun, so it's something I've been postponing a long time now. I gave him my Prunes and Custard clone to keep him happy.

Some slider potis have broken off, which in itself is not a problem, but testifies of the hardship the box has been through. Maybe the potis have internal damage too. Was reluctant to take it completely apart, but there is no choice now.

Do you want detailed pcb pictures?

It seems I should be able to find one under 50 EUR even.
What are you waiting for ?

analogguru


Just some good luck and a local auction to avoid a large shipping fee :mrgreen:
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 28 Aug 2008, 15:23

There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
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Re: Should I buy a cheap oscilloscope?

Postby modman » 31 Aug 2008, 12:18

Thanks AG! Just what I needed.

Checked some auctions and tis really true the 100 EUR budget that would get me at least a 20Mhz dual channel on ebay, wouldn't even buy me a new 1 channel 10Mhz step in model at Conrad:
2 channel 20Mhz

http://www.conrad.be/goto.php?artikel=120632

OSCILLOSCOPE-HAMEG-203-4 2 channel 20Mhz at 57 EUR
Tektronix-465-Oscilloscope-Dual-Trace-100-MHz sold at 97 EUR
Oszilloskope-TEKTRONIX-453-Dual-Channel-50-MHz sold at 86 EUR
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Re: Should I buy a cheap oscilloscope?

Postby RLBJR65 » 31 Aug 2008, 17:26

I've been meaning to scan these :wink: More reading material!
http://sites.google.com/site/diyjunkie/ ... edirects=0
http://sites.google.com/site/diyjunkie/ ... edirects=0
http://sites.google.com/site/diyjunkie/ ... edirects=0
http://sites.google.com/site/diyjunkie/ ... edirects=0

I've got an old Fairchild / Du Mont 304A. It's a tank, all tube made in the late 50's. Sadley it no longer works.
One of these days I'll pull all the tubes and test them. It also has a couple of pots that need replaced. I suppose all the electrolytic caps should be changed as well.

I got it free but I'm not sure it's really worth rebuilding.
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 31 Aug 2008, 19:38

I've got an old Fairchild / Du Mont 304A.

Does it already have trigger ?
I have an old Heathkit tube oszilloskop which doesn´t have trigger, only sync.

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Re: Should I buy a cheap oscilloscope?

Postby RLBJR65 » 01 Sep 2008, 16:40

analogguru wrote:
I've got an old Fairchild / Du Mont 304A.

Does it already have trigger ?
analogguru


:oops: Don't know... I think only sync.

I know next to nothing about scopes the only times I have used one were with sombody who actualy knew what they were doing.

Here is a pic of mine http://sites.google.com/site/diyjunkie/ ... edirects=0
and here is a Q&D scan of the manual http://sites.google.com/site/diyjunkie/ ... manual.pdf

I have all adjustments set per startup in the manual.
When I turn it on and it is warming up there is a dot in the center of the screen that quickly travels towards 7 - 8 o' clock then off the screen.

I tried hooking up a 3 vac transformer to play around with it also tried a square wave 555 circuit but had no luck getting it to do much with either.

I would love to have a working scope because I think it would be a great learning tool.

Do you think mine is worth trying to repair? I would hate to spend a bunch of cash and time on it only to be disapointed later.
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 01 Sep 2008, 21:41

Do you think mine is worth trying to repair?

If you expierience it as fun to play around with old tube equipment: yes
From an ecomonical viewpoint: no

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Re: Should I buy a cheap oscilloscope?

Postby RLBJR65 » 01 Sep 2008, 22:33

Thanks analogguru that’s what I figured and I guess that is my dilemma, I want to fix it but...

Guess I'll open it up and poke around a bit :wink:

Do you have any recomendations as to how I should proceed or what to check out first?
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Re: Should I buy a cheap oscilloscope?

Postby modman » 02 Sep 2008, 14:03

I'm still reading that little book, but some more questios that are not addressed there:

If I buy a scope without probes, how do I find ones that match? Is there a standard for connecting the probes?
Do modern oscilloscope allow for calibration/setting up if necessary? A lot of 'untested' items on ebay... :hmmm:
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Re: Should I buy a cheap oscilloscope?

Postby analogguru » 04 Sep 2008, 10:37

RLBJR65 wrote:Do you have any recomendations as to how I should proceed or what to check out first?

I am very busy at the moment, must have a look at the schematic first...

modman wrote:If I buy a scope without probes, how do I find ones that match?

You can buy every probe that has at least the same upper frequency than the scope.... for audio frequencies unimportant.
modman wrote:Is there a standard for connecting the probes?

The old standard (up to the sixties) was two banana plugs - the new standard is one BNC-plug.
modman wrote:Do modern oscilloscope allow for calibration/setting up if necessary?

The probes normally allow this - there is a little trimmer inside the probe. The calibration is done (on Hameg scopes) with the build in square-wave generator.

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Re: Should I buy a cheap oscilloscope?

Postby RLBJR65 » 04 Sep 2008, 18:28

Thanks analogguru.

I think I figured a plan.
1: Pull all the tubes and test them.
2: Replace tubes as needed. I've got about half of them anyway. Most are used but good.
3: Check and or replace the electrolytic caps in the horizontal circuit.

Hopefully that will get me going without spending a ton of money.

Sorry for hijacking the thread Modman!

I have another book around someware that has add on test circuits etc. for oscilloscopes when I find it I'll scan and post it too.
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Re: Should I buy a cheap oscilloscope?

Postby modman » 08 Sep 2008, 23:29

[quote="RLBJR65"
Sorry for hijacking the thread Modman! [/quote]

Hey, R, don't worry - it's relevant discussion, because tube scopes cost nothing nowadays - nobody wants to bother with them it seems. If you keep us updated on your endeavours.

Anyway, I went the a bit less cheaper way, but I think I scored well with a 2 channel 20Mhz scope for 38,50 EUR and it seems to work (let's find out when I get it.)
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Re: Oscilloscopes for dummies

Postby DiscoFreq » 04 Oct 2008, 18:00

Good place for my question!

I have a vintage Polish mini-scope, but no probes, can I use anything for that? I bought it a year ago (or longer) but still didn't test it :scratch:

(I wanted to build it into my modular synth, it's the perfect size for that: about 5U high 8))

picture is not mine, but same model...

mini-osc.jpg
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Re: Oscilloscopes for dummies

Postby Dirk_Hendrik » 04 Oct 2008, 18:34

Great spot for my question too!!
Could you (modman) please adapt your explanations so they're usable for my daily bread and butter over the last 2 years:
Image

(4Ghz bandwith, Mhz bandwith starts to feel like DC then ;) )
Sorry. Plain out of planes.

http://www.dirk-hendrik.com
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Re: Should I buy a cheap oscilloscope?

Postby RLBJR65 » 14 Oct 2008, 21:14

RLBJR65 wrote:it's relevant discussion, because tube scopes cost nothing nowadays - nobody wants to bother with them it seems. If you keep us updated on your endeavours.
I got mine FREE cant get any cheaper than that :wink: My parents moved into a smaller place so Dad gave me the scope a Heathkit capacitor substitution box, a Heathkit resistor sub box and a Micronta transistor tester like this one http://cgi.ebay.com/Transistor-Tester-M ... 286.c0.m14 that I have not figured out how to use yet.

Anyway... I finally got around to checking the tubes. The 1X2A rectifier (V604) that supplies -1400v to the picture tubes plate is bad. It tested at 60% or so also the gas and short lights were flickering. All the other tubes tested at 85% or better! At my favorite surplus store I picked up an NOS 1X2A for 2 bucks :D

Hopfully I will get a chance to put it back together and try it out this weekend.
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