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-   -   Is this a good deal on an o-scope? (http://www.diyaudio.com/forums/equipment-tools/192484-good-deal-o-scope.html)

caxxxxxx 12th July 2011 01:52 PM

Is this a good deal on an o-scope?
 
I came across a B&K 1471 dual trace scope and a HP freq counter, $75 for both. He says they both work like new. Is this worth checking out, theres not much info out there on the B&K, and I don't know what a frequency counter is yet, lol. He didn't yet state the model # of the feq counter.

Thanks
John

firechief 12th July 2011 03:20 PM

Sounds fair, and the scope us likely to be useful. What is the model of the frequency counter? It can be used in conjunction with the scope to measure the exact frequency of a signal. Best move is to have a knowledgable person check it out before buying. even though that is not always easy.

caxxxxxx 12th July 2011 05:30 PM

Quote:

Originally Posted by firechief (Post 2636699)
Sounds fair, and the scope us likely to be useful. What is the model of the frequency counter? It can be used in conjunction with the scope to measure the exact frequency of a signal. Best move is to have a knowledgable person check it out before buying. even though that is not always easy.

I'm still awaiting a response on the model number of the frequency counter.

Unfortunately, I know no one that can help me out on the scope. Is there anything I should look for? What does the average audio electronics hobbyist look for/need in a scope?

tomchr 12th July 2011 07:58 PM

A regular 20 MHz scope will be fine for audio (and slower micro controller debugging) use. Beyond that is icing on the cake.

When you turn on the scope, ground the input (using the ground switch) and verify that the intensity and focus knobs work. You should be able to tweak the intensity of the displayed trace from complete dark to burn-out bright and you should be able to focus the trace into a crisp line.

When turning the time/div knob you should be able to get the time scale slow/long enough that the trace turns into a slowly moving dot that moves from left to right. Usually the slowest time base will make the dot move across the screen in about five seconds. Turning the time/div knob the other way will cause the dot to move so fast that it forms a trace on the scope screen.

Vertical adjustment knobs should move the trace up/down. Horizontal adjustments should move the trace left/right.

The scope should come with probes. Attach a probe to one of the inputs and DC couple the input. Attach the probe to the CAL output of the scope (if it has one). It should say by the CAL output (typically a little eye or test point on the front of the scope) what signal levels and frequency to expect. Verify that you get the right signal level and frequency. The CAL signal is typically a square wave and should show as a clean square wave trace. If the corners of the square wave are 'pointy' or rounded off that means the probe needs to be calibrated (simple DIY job using a plastic trimmer tool on the tuning capacitor in the probe head - see the manual for the probe or o'scope).

If you're completely new to oscilloscopes, I suggest looking at an online tutorial before you meet with the seller.

A frequency counter can be handy. If nothing else, then because it usually contains a precision frequency reference. In some cases this reference oscillator is temperature controlled - hence, drift very little over time. However, the accuracy of the frequency measurements will depend on the accuracy of this reference. If at all possible, I would get that reference calibrated against a known frequency.

~Tom

tomchr 12th July 2011 08:01 PM

using an oscilloscope

YouTube - ‪Oscilloscope demo‬‏

dchisholm 12th July 2011 09:09 PM

'Scope Checkout
 
1 Attachment(s)
ANY working 'scope is at least 100 times better than NO 'scope.

The instrument probably has an internal signal for probe compensation and rough calibration - usually a squarewave at 1 KHz or 10 KHz, and a particular amplitude somewhere between 1V and 10V pk-pk. Use a 10X probe to view this signal. Adjust "Focus" and "Brightness" to get a usable trace. Set position controls, vertical sensitivity, horizontal sweep rate, and trigger controls to get an on-screen display.

On the probe body, or probe connector, you will find an adjustment to optimize the frequency response of the probe as connected to that particular 'scope channel. Adjust it for the best squarewave display. (The atch image of a 'scope display illustrates a typical range of adjustments.)

You should see a stable, crisp, well-defined trace - without "fuzz" (either noisy vertical amplifiers, or problems in the display circuits), and without ripple (power supply problems, such as worn out electrolytic capacitors, or an EMI/RFI problem). If there is significant horizontal jitter there may be problems with the trigger circuits.

You should be able to get a readable display for 3 or 4 different settings of vertical and horizontal sensitivities. The displayed amplitudes and periods should track reasonably well from setting to setting. (The absolute accuracy of a 'scope isn't fabulous - seldom any better than 5% - but the range-to-range tracking of vertical and horizontal settings should be better than that.)

Repeat these test for both vertical channels if it's a dual-trace instrument.

If the instrument has additional features, like delayed-sweep, trace arithmetic, X-Y display mode, etc, you can do a quick check of their basic functionality. Depending on your particular interests, these features may or may not be useful.

In my opinion, the biggest practical difference between the really good 'scopes and the rest of the pack is in the triggering system. I don't know of any particular test to evaluate this function - it's something that you develop a "feel" for, especially as you work with complex waveforms. Every genuine Tek 'scope I've used for nearly half a century has had stable, effective, triggering functions that were compatible with the instrument's basic capabilities. 'Scopes from other manufacturers have also had good triggering performance, but not as consistent from model to model as the Tek products.

Dale

VictoriaGuy 13th July 2011 08:25 AM

I've got a B&K scope- not the same model- and it's been a simple and reliable tool for me.
If it has:
Probe or better- probes
Manual
and is working....
$75 seems very reasonable, IMO.

The seller should be willing to demo if he states they are working 'as new'.
The HP freq counter is an 'extra' and you can always re-sell it if you don't need it...as long as it is working.

I looked at the B&K website and apparently you can request manuals for older equipment.

caxxxxxx 13th July 2011 02:12 PM

Thanks so much for taking the time for the info, that youtube vid helped a lot. I might actually be able to use one of these now.

He just emailed back and lowered it to $50 for both. I think that sounds great. I'm gonna look at it tonite if possible.

The freq counter is a HP model 5245L. I don't think anyone will buy it unless I get really lucky but hey, an added bonus!

These are both dinosaurs, but should work well in my environment.

VictoriaGuy 13th July 2011 07:06 PM

That 5245L is a very cool looking piece of gear- will impress the h**k out of visitors to your shop! Just hang it on the output of your signal generator.

dchisholm 13th July 2011 11:09 PM

Quote:

Originally Posted by caxxxxxx (Post 2637706)
The freq counter is a HP model 5245L.

If the 'scope is functional, $50 sounds like a fair price - especially if it has a probe or two.

Speaking for us dinosaurs . . . the only bad things about the 5245L are the physical size, and the requirement for AC power. As already mentioned, the Nixie tube display definitely has a mad-scientist mystique. In some circles the Nixie display assembly has value all by itself. The 5245L was already obsolete when I was using them 30 years ago - but the mainframes were reliable performers. (The heterodyne downconverter plug-ins that extended the counter range into microwave bands were another story.) I think some of the 5245L's had a high-precision timebase oscillator, but even the standard timebase might be the most accurate frequency standard you're likely to have in your workshop.

Dale


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