Trying to decide between three scopes - Page 1
Forum section: electronics / testgear

author: vexatag
author_rank: Regular Contributor
timestamp: June 30, 2020, 09:33:06 am
content: I'm trying to get a cheap (<$50 if possible) 20Mhz+ two channel scope for my first foray into EE and construction of DIY analog synthesizers. My candidates so far arehttps://www.ebay.com/itm/GoldStar-OS-9020A-Oscilloscope-20MHz-2-Channel-Oscilloscope-Test-Equipment/264658346949This one is generating a trace, and seems to be fairly well-documented on here. I'm somewhat worried about potential damage in shipping especially after the seller told me my only recourse would be "fighting with the carrier".https://www.ebay.com/itm/224028068176This one only seems to be generating a point, plus it feels somewhat risky to trust free shipping of anything with a CRT diagonally across the USA. It does seem to be fairly well-documented as well.https://www.ebay.com/itm/Tenma-Model-72-6810-50V-Cat-II-Oscilloscope-READ/164261205195This one apparently turns on but is missing all of the position knobs and it's the worst-documented out of my options (I have a hard time even confirming that it exists and manuals beyond a basic data sheet do not seem to exist). The only advantage it has over the others (besides resolution) is that the seller is one city over from me in the PDX area so I could pick it up in-person.If anyone has other options I'm definitely open to them. Thanks for reading and I'm glad to be part of this group.

author: tv84
author_rank: Super Contributor
timestamp: June 30, 2020, 10:04:42 am
content: With those scopes you won't be doing any "construction of DIY analog synthesizers" anytime soon... If this is your first foray into EE, then get yourself a working unit!

author: vexatag
author_rank: Regular Contributor
timestamp: June 30, 2020, 10:11:20 am
content: Quote from: tv84 on June 30, 2020, 10:04:42 amWould that I could, my budget is super limited and these are the only 20 mhz scopes that I can find in my budget, even checking on Craigslist and Facebook marketplace.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 30, 2020, 10:19:52 am
content: For DIY analog synthesizers, as a start you can use any soundcard available in a PC and some freeware software, e.g.https://www.zeitnitz.eu/scope_en

author: vexatag
author_rank: Regular Contributor
timestamp: June 30, 2020, 10:21:47 am
content: Quote from: RoGeorge on June 30, 2020, 10:19:52 amOoh, I'll be sure to check that out, thanks!

author: Fungus
author_rank: Super Contributor
timestamp: June 30, 2020, 10:11:51 pm
content: Quote from: RoGeorge on June 30, 2020, 10:19:52 amThis!Add a potentiometer for volume control so you can look at the 12V outputs that some of them have.If you want to do FFTs then this software works well:https://store.digilentinc.com/waveforms-download-only/

author: vexatag
author_rank: Regular Contributor
timestamp: June 30, 2020, 10:20:01 pm
content: Sound card scopes only go to 44khz at most but the process book I'm reading (Make: Analog Synthesizers by Ray Wilson) recommends a minimum bandwidth of 20mhz. Is this an actual concern or was the author overcautious in his recommendation?

author: nctnico
author_rank: Super Contributor
timestamp: June 30, 2020, 10:22:54 pm
content: I have a feeling that a 'pocket DSO' is a better deal in this price range.Something like this for example:

author: tv84
author_rank: Super Contributor
timestamp: June 30, 2020, 10:49:35 pm
content: Quote from: vexatag on June 30, 2020, 10:20:01 pmBy a factor of aprox. 500...I wonder why...The author also says (in the same page): "The bottom line is this: buy the highest bandwidth DC-capable scope you can afford."BTW: Just foundthis.

author: bdunham7
author_rank: Super Contributor
timestamp: June 30, 2020, 11:46:53 pm
content: Of the 3, just by looking at the pictures, the Goldstar is the most likely to yield you a working unit.The Tenma is junk by now, I think you'll find that it has been dropped and more is missing than just the knobs.The BK I'm familiar with--I recently overhauled one--but that one looks a bit rough. If you are considering it, ask the seller to push the 'X-Y' button once and see if that dot goes away.If an eBay seller tells you that you'll have to 'fight with the carrier' in case of damage, they're new. The seller is 100% responsible for getting it to you in one piece. Unfortunately, if they are new, the probably don't know how to pack an oscilloscope. I sometimes get free or heavily discounted equipment this way.

author: vexatag
author_rank: Regular Contributor
timestamp: July 01, 2020, 03:22:21 am
content: Quote from: bdunham7 on June 30, 2020, 11:46:53 pmThank you for the info, I messaged the seller of the BK and will report back if I hear from them.Quote from: bdunham7 on June 30, 2020, 11:46:53 pmThat is good to know as well.

author: Fungus
author_rank: Super Contributor
timestamp: July 01, 2020, 06:11:52 am
content: Quote from: vexatag on June 30, 2020, 10:20:01 pma) Not true. They go to whatever sample rate the sound card is capable of. These days it's easy to get 96kHz or even 192kHz.b) I don't think the recommendation is for looking at the audio signal, more like general 'scope buying advice.

author: vexatag
author_rank: Regular Contributor
timestamp: July 02, 2020, 01:36:52 am
content: Small update, I'm browsing Yahoo Auctions through a handling service and very impressed at the selection of cheap analog scopes that are being listed (finding many in the $10-60 range). Granted, shipping and fees will most likely drive the cost up somewhat but this is looking like a promising avenue.

author: nctnico
author_rank: Super Contributor
timestamp: July 02, 2020, 10:40:21 am
content: Why aren't you using a way to find a scope local to you? I guess Craigslist still exists. At least you can go over and pick it up. In an auction handling fees and shipping easily add an extra $50 at which point you can buy a cheap digital scope including free delivery.Or get a USB scope...At $60 this is hard to beat:https://www.ebay.com/itm/Hantek-6022BE-PC-laptop-Based-Digital-Oscilloscope-USB-48MSa-s-200MHz-USA-SELLER/363029496612

author: vexatag
author_rank: Regular Contributor
timestamp: July 03, 2020, 08:14:33 pm
content: Quote from: nctnico on July 02, 2020, 10:40:21 amI checked my local listing sites and no one is selling any in my budget

author: vexatag
author_rank: Regular Contributor
timestamp: July 03, 2020, 08:15:25 pm
content: I bought the BK, here's hoping it's not a cluster of a project)))

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: July 04, 2020, 11:35:13 am
content: Oh dear, I wish you well but fear that was not a great purchase. Even if you get it to work, you've got a very old CRT scope.Happy Independence Day anyway.