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Old 1st February 2011, 08:17 AM   #21
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+1 dragon. As they say in racing "all the gear and no idea"

Get a simple scope that will do all the basics - it worked for all the guys in the high end of electronics in the 1950s which is the period your tube amps hail from.

Once you've got the hang of it and when you feel the need, invest upward - they will ALWAYS get cheaper (just like any electronics) so there is no need to rush.
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Old 1st February 2011, 08:33 AM   #22
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An analogue 'scope has the ability to show "infinite" detail within the limits of it's spec and how clear the trace is.

Digital is more limited, particularly at the money we are talking here. Think of it as viewing a .jpg with limited resolution... you can't see the fine detail.

The shots below are hardly a challenge for any analogue 'scope,
The best sounding audio integrated opamps
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Old 1st February 2011, 08:34 AM   #23
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Quote:
Originally Posted by manp111 View Post
I understand.

Any specific model?
Again, rather than focus on a specific model, look for something that meets the minimum requirements, dual trace and at least 20MHz.

As already advised, try to get one with a known history, or at least see it working before parting with cash. Also check that the probes are included in the price! They can sometimes cost more than the 'scope itself.
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Old 1st February 2011, 10:17 AM   #24
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I bought my first 'scope from 'Radio-Shack'--A vey simple single-channel thing, 5 meg bandwidth but bright sharp trace.....

Dispite its limitations, I was still able to use it for many years in TV Video servicing--When people had stuff repaired, Remember those days!

Even fully aligned a PAL colour decoder in a mostly valve Philips G6 tv with that....

A few years ago, I bought a Tek 454 dual-channel 50M scope from fleabay cheap, All working but with a pretty worn CRT...

Some hunting round on the web found a new CRT in a test-instrument house in New-York...
Got that and fitted it, Its been great ever since....

Loverly quality old machine....
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Old 1st February 2011, 11:28 AM   #25
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Nothing really compares to a Tektronix analogue scope.

I've got a particular fondness for the 4XX series (465, 475, 485, etc) having owned and/or used them for many years.
The 453 and 454 are also worthy of mention, as they don't use an Tek-specific parts.

I see you're in the US, so you should have a lot less trouble finding a decent analogue scope than we do here in the UK.

You definitely want dual trace (so you can compare the input and output of an amp)
And you can't have too much bandwidth, although 20MHz is recommended as a minimum, 50MHz is more of an ideal.
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Old 1st February 2011, 12:51 PM   #26
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Agreed on getting an analogue scope and preferably a Tek. I will say that I would avoid the really old scopes now... like a 453 (sorry tunneldiode). I had one for decades when I was in field service. Truly a superb scope for it's time and amazingly reliable (large and heavy vs screen size). After lots of heavy use (I wasn't the first owner) it eventually started to show it's age with controls getting noisy/flaky and other issues associated with old age. If you manage to find a very well maintained one that's been lightly used, then great, otherwise...

I'm currently using a Tek 2215A which is an excellent and affordable scope. I've got a couple of these. The last one I picked up on ebay about 4-5 years ago... essentially NOS, in the original box with probes, manual, line cord and even the serial number handwritten on the box matches the unit. I think I paid $350 for it.

Regards, KM
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Old 1st February 2011, 03:13 PM   #27
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Manp111: Craigslist is a good place to find a decent used one. Expect to pay around $75-$150 for your basic CRT 20Mhz two channel model. Then there is always Ebay, but the nice thing with Craigslist is that you can try before you buy.

I purchased a basic no-name (Elenco) 25Mhz 2 channel CRT scope from a member here on the swap meet last year for $75, and it works great. It appears to be fairly common and sold under several brand names.

I also have a Tek Digital scope (older Black & white display, 60 Mhz 2 channel) that I bought from a previous employer, and it is nice, with a few more bells and whistles than the scope above.

Finally, I just bought a cheap ($450) B&K digital scope for work very recently (a B&K 2350) with a fancy color screen, 25Mhz, 2 channel, FFT, etc. and my first observation is that the screen is a bit lo-rez. It has lots of bells and whistles, though, like an auto setup button and the ability to do a screen capture to a usb drive with the push of a button. It also displays various things like Vpp and freq, etc.

I presently use my older CRT scope way more than the DSO scope, mostly because I'm more familiar with it. You'll probably learn more using a basic scope that doesn't do auto setup, etc.

One final thing, if you are planning on using it for tube amps a 10:1 600V probe is very handy, as most scopes are rated for 300 or 400V max input. A clip lead type probe is also nice.
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Old 1st February 2011, 03:22 PM   #28
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THIS scope on craigslist locally would be nice scope if it works properly. The most basic calibration issues are covered in the manual and are within a DIYs abilities. Take a knowledgeable friend with you and have a look. Pass on it if the trigger or the square wave function does not work.
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Old 1st February 2011, 05:56 PM   #29
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My 20MHz Hameg 205 analogue has been a bench workhorse for 35 yrs with lovely green trace with simple trace save. As I do alot of switchmode work, a modern Tekt 2022 deals with fast risetimes, glitches and more storage/recall facilities. As FFT mode is always now incorporated in most digital scopes, watch out for the vertical resolution ability when doing important spectral analysis. Many digi scopes offer 8 bit vert resolution on FFT which will give unpredictable results for delving harmonics lower than -50dB. i.e 256 steps; while a 12 bit with 4096 steps will give accurate results to around -74dB which can be extended with some tricks. The more resolution the more price.

In a nutshell, if you wanna to keep things simple, then a good analogue scope may be enough and simply use a pocket camera for the screen details. It won't have alot of the diversity that a digital offers, screen details, cursor, frequency & time automatically displayed (avoiding external frequency counter etc) and direct USB interface to notebook for records. There's alot to the learning curve, after all that's what electronics is all about, but if one can copy & paste articles on the diyAudio forums, then a USB scope is already half way there.

The seductive smooth green trace of a Tektronix or a Hameg is irresistible in the evening light. Is it giving all the info ?

richy
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Old 1st February 2011, 07:06 PM   #30
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I'm glad all the above users except richwalter are rich. I loved my tek 466 memory scope at work, but I have never seen one around here on CL. I will not buy a scope on Ebay, you have to look for burned spots on the tube and check out the trigger circuit before purchase to see that it still produces a stable waveform. I use a transistor radio with plug in the earphone for trigger check. My B&K 2120 cost $40; it was fished from the dumpster at the local radio-TV school and does fine on audio and organ projects. It is 20 mhz and dual trace, totally obsolete for computer work but fine for audio.
Non-vacuum tube scopes are hyper sensitive to dropping, light enough to be yanked off the table by snagging the probe with your pants, and one drop of water will take out the screen. See posts about repairing the screens on "everything else'.
PC "scopes" involve the PC in the grounding circuit, and PC's are notorious sources of RF etc. Also having a grounded scope can be unsafe on defective HV circuits. My B&K ground appears to be isolated from the power line, which is very good.
Cheap 10:1 scope probes ($53 minimum) like stocked at mouser.com are limitied to 300 V, so no good for tubes. There are 100:1 probes that are rated better, but not real cheap. Tek probes start over $100. You need two for any serious problem.
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Last edited by indianajo; 1st February 2011 at 07:09 PM.
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