HP 1725A Oscilloscope--Curve Tracer Function?! - diyAudio
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Old 6th September 2012, 04:00 AM   #1
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Location: Toronto, Canada
Default HP 1725A Oscilloscope--Curve Tracer Function?!

Hi all,

I bought this oscilloscope five years ago locally and it's been great! I lent my oscilloscope out to a friend for his grandfather to use. When I got it back I was re-integrating it into my bench and getting my setting back to where I keep them until I noticed one function that I hadn't taken note of before...

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As far as I can tell there are no curve tracer specific inputs, additionally the manuals I've been able to find state nothing of an option H01 (option 101 includes the 1607A logic-state analyzer inputs), but if you look at the first photo, this was a unit built for amdahl.

Pulling the intensity knob to enable the curve tracer mode, the line becomes a point, and it positions itself on the far left of the screen, one major division from the edge, and one major division below the horizontal zero line.

This is a photo of what I consider to be a 'normal' 1725A: http://www.amplifier.cd/Test_Equipme...725A_front.jpg

There's also another HP 1725A on eBay (#290760536448) right now with the 1607A inputs on the back, but without the curve tracer writing on the faceplate... ?!


I have yet to play with this mode (bit busy) but I thought I might post it up here just in case anyone has seen this before! I'm quite excited as I've been shopping for a Tek curve tracer, but they tend to sell for 5x my budget!

Has anyone every seen this before?


Philip.
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Old 6th September 2012, 05:30 AM   #2
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I wonder if it allows you to use one vertical input for Y axis and the other for X axis. Try feeding the same signal to both inputs with equal gain settings and see if you get a line at 45 degrees.
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Old 6th September 2012, 07:30 AM   #3
Enzo is offline Enzo  United States
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SO put it in that mode and try inputting signal to those 1607 inputs on the rear.
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Old 6th September 2012, 07:54 AM   #4
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Quote:
Originally Posted by Enzo View Post
SO put it in that mode and try inputting signal to those 1607 inputs on the rear.
No, I was thinking of the two inputs on the front panel.
The 1607 inputs appear to be dedicated to an optional logic state analyser.
Still, it's worth a try. I just had a quick look at the 1607 description and it does appear to output an analog signal.

Last edited by Bibliophile; 6th September 2012 at 08:11 AM.
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Old 6th September 2012, 03:12 PM   #5
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There is an XY mode (bommom of the blue buttons in the centre) and at the time I discovered that mode I was looking at the Lissajous figure of a tuner's MPX out--putting it into the curve tracer mode with the tuner still hooked up and turned on resulted in a dot.

Here's something I found interesting, however... on the eBay oscilloscope with the 101 option (1607A inputs), the Z input on the back has a sticker over it stating that it's a 1697A input, while mine does not have this sticker. Another 'built for amdahl' model is also on eBay right now (#180646030393) and it shows the same sticker missing on the back; this is at least a bit of confirmation that the sticker on mine wasn't peeled off!

Maybe the X, Y, and Z inputs are used for the C, B, and E inputs...

There really needs to be more hours in the day--I won't be able to pop the cover until mid-to-late next week.


opt101 and opt003:


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Click the image to open in full size.



Amdahl optH01:


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Old 6th September 2012, 03:22 PM   #6
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Oh! Another thing I noticed is that on the 'normal' (opt101) oscilloscope, the time interval area (top right) has a multi-turn potentiometer with what appears to be a vernier dial (labelled as 'STOP'), while on my 'scope and the other optH01 example, that appears to be replaced with a dual-concentric potentiometer (labelled 'OFFSET').

Another round of spot-the-difference and we find that the CAL test point on the bottom edge, in the centre, states 'CAL 3V' on a 'normal' 'scope, and 'CAL 1MHz/1uSEC' on mine as well as the other amdahl unit on eBay, although I imagine that this is insignificant.
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Old 6th September 2012, 04:36 PM   #7
Enzo is offline Enzo  United States
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"No, I was thinking of the two inputs on the front panel."


Biblio, I know what you meant. The OP also posted on this in another forum and reported having tried the XY inputs. My suggestion was just an alternative idea. Those rear panel inputs may have been intended for a logic state analyzer, but that doesn't mean they were no also used for this custom application. SInce they are marked horizonal and vertical, they seem like they would also be some sort of XY inputs


I could be wrong, but I'd suspect that a component curve tracer would have been an accessory unit - an exterior fixture. After all, to trace curves on a transistor, one needs voltage and current sources, which would not have come from the scope inputs.
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