Oscilloscopes - Are they important and what Kind is adequate

[RJ Guitars]

Hey all,

I've always done amps scopeless... just curious what I could accomplish if I had one and further... what is the affordable scope that is adequate for a home builder?

Is the mojo all in the ears and too much technology an impediment?

What about these computer based O'scope cards?

rj

[LeftyStrat]

It's one of those tools that once you've learned to use one, you wonder how you ever got along without it.

You can usually pick up a nice old Tektronics scope off eBay for cheap. I don't have any experience with the computer based ones. If you go the computer-based route, make sure it is isolated from the computer. You're going to be poking around a live amp, last thing you want is to send 500 volts into an expensive computer.

It's most obvious use is debugging. Say you've got some weird overtone or buzz on your signal, you can examine the output of each stage and find which stage is causing problems.

But for me it also helps in understanding amps, seeing where the "mojo" is coming from. By examining the output of each stage, you can see when flattening of the waveform starts occurring (clipping) and at what stage in the amp. You can also look at things like PI balance.

It doesn't replace your ears. But I think it can enhance your ears by giving you visuals to go along with what you are hearing.

[Fischerman]

You'll also need a signal generator and 10x probes if not included with the scope. I recently bought an old Kenwood 20MHz dual-trace scope and some off-brand signal generator off of e-bay. Both are from the 70s or maybe 80s. The Kenwood is only 20MHz but that is supposedly plenty for audio work. I paid under $200 for the pair and they work perfectly. And this stuff is built to last.

When I was shopping I was warned to stay away from the really old tube units and try to make sure there is some sort of recourse if it doesn't work. Many auctions will say stuff like; "This was my grandfather's...as far as I know it works but I don't know how to test it." and I stayed away from those. Mine were from some repair shop in CA that was closing down or something...they were 'tested good'.

Still learning how to use it but just looking at the waveform throughout the amp is simple enough.

[El_Martin]

Hi!

I really like my old HAMEG. I often use the built in component tester and the handy test signal.
Component tester uses AC and checking of lots of components is possible "in circuit".
Somebody throw it away. They checked it and did not realize it was working correctly.

it's a nice-to-have unit.

No, I didn't use it for biasing, yet...

Ciao
Martin

[skyboltone]

I'll plus one on the Tektronics. They are the gold standard. A 453 is more than adequate and they just about grow on trees. Make sure it works though, that is one complex device. I think I paid more for the probes than I paid for the scope. Try to get one with a 10X probe. More if possible.

[LeftyStrat]

Another good option if you're the fixit type, is Free Cycle:

http://www.freecycle.org/

My wife is on the mailing list and people give away all kind of stuff. She scored a B&K 707 Tube tester for me, free! It wasn't working, until I put a new fuse in it

Only thing was, the guy giving it away insisted that I also haul off a B&K 850 Color Analyst. Turns out it had several 6AN8A's that still tested strong.

[John_P_WI]

I use a Hitachi (30Mhz) from the late 80's that is built like a tank. Definitely get a 10x probe if you are probing any plate or high voltage circuits. Most scopes have a 300 V max input. (This is my 3rd scope as I keep upgrading.)

To get the most out of it you need a signal generator (as mentioned above). The scope + signal generator really help setting up high gain stages with proper interstage attenuation.

John

[LOUDthud]

You won't get many hits on ebay unless you spell the name correctly. It's Tektronix. I used to work there and some of the employees couldn't spell it

[mhuss]

I use a Hitachi (30Mhz) from the late 80's that is built like a tank.

Me too! Keeps going and going.

Definitely get a 10x probe if you are probing any plate or high voltage circuits.

To get the most out of it you need a signal generator (as mentioned above). The scope + signal generator really help setting up high gain stages with proper interstage attenuation.

+1

--mark

[jjman]

I just picked up the Tektronix 2246 which has 4 channels for $300. You don’t need 4 channels but you definitely want no less than 2. They are plentiful and new listings come up on ebay literally every day. The selection of probes out there is confusing. Don’t buy the non-Tektronix brand 10x probes if you want to avoid having to divide the display voltages by 10 in your head. Even some of the Tektronix brand 10x probes won’t correct the display factor if it doesn’t have the “reader” pin sticking out of the BNC connector.

Here’s a nice site with many of the probes and their specs:

http://www.barrytech.com/tektronix/prob ... robes.html The “scl read” is the pin. No pin is appropriate for 1x.

[LeftyStrat]

Good old Tone Lizard also has a section on scopes, as well as many other sections:

http://www.tone-lizard.com/

Idiots guide to scopes:

http://www.tone-lizard.com/Oscilloscopes.htm

[drz400]

Cant go wrong with a 465B

I definately think they are a must unless you like exploritory surgery

You wont need one until you have a problem

[RJ Guitars]

Thank you all... i've been away from my work desk for a few days, but these are great notes and I'll start looking for one of those recommended bargain scopes...

Possibly someone could follow-up with one of those "How you do it" posts on the basics of using an oscilloscope??

rj

[Sonny ReVerb]

Here's a good place to start:

http://www.tek.com/Measurement/App_Note ... 8605_2.pdf

[LeftyStrat]

Possibly someone could follow-up with one of those "How you do it" posts on the basics of using an oscilloscope??

Omar is working on getting the Amp Garage Wiki set up. I will add my limited knowledge using scopes there, and I'm sure others will contribute.

If you search for "Oscilloscope Tutorial" you will find some good info, but I think the Amp Garage Community could probably produce some info more focused on using the scope for amp work.