Help with Basic Circuits

WBahn

Joined Mar 31, 2012
29,843
You say you bought 70s to 90s test equipment. You don't see any value in the newer digital oscilloscopes ? (for your electronics hobby).
Speaking for myself, it's not a matter of whether there is any value, it is whether the value-to-cost ratio warrants it. If the equipment you have is good enough for what you are trying to do, then better equipment has very little actual value because you can already make the measurements you need to and do so to a degree that is good enough for your needs -- how much value is there when the new equipment doesn't allow you to make any measurement that you need to make that you can't make already? On top of that, older equipment can often do things that newer equipment can't -- for instance, there is an easy way to use an analog oscilloscope to get a pretty good idea of the linearity of a circuit in just a few seconds that can require a huge amount of data acquisition and analysis with most digital scopes. Furthermore, there is the question of ease-of-use when working with equipment you are familiar and comfortable with.
 

Thread Starter

RUSTYWIRE

Joined Aug 28, 2023
61
Speaking for myself, it's not a matter of whether there is any value, it is whether the value-to-cost ratio warrants it. If the equipment you have is good enough for what you are trying to do, then better equipment has very little actual value because you can already make the measurements you need to and do so to a degree that is good enough for your needs -- how much value is there when the new equipment doesn't allow you to make any measurement that you need to make that you can't make already? On top of that, older equipment can often do things that newer equipment can't -- for instance, there is an easy way to use an analog oscilloscope to get a pretty good idea of the linearity of a circuit in just a few seconds that can require a huge amount of data acquisition and analysis with most digital scopes. Furthermore, there is the question of ease-of-use when working with equipment you are familiar and comfortable with.
What is the issue about the newer digital scopes that brings up the ease of use factor related to "data acquisition"
or other features of the newer scopes?
Or is it just about the familiarity factor you are talking about?

Thanks
 

Thread Starter

RUSTYWIRE

Joined Aug 28, 2023
61
Not really. I have several 7D20 70MHz digital scope plug-ins for Tektronix 7xxx series oscilloscope mainframes. I have a 2 channel HP 15xxx series 2GSa/s scope that's not even worth the bother of using. I have a 20MHz Hantek USB scope that someone gave me. He never used it and neither have I. I also have a few of the 100KHz-1MHz DSO toys. I bought them just to see what all of the fuss was about.

The scope I use the most is a Tek 7704A 200MHz mainframe with 2 7A26 vertical amplifiers (4 channels total at 200MHz) with a 7B53A time base (that limits the system to 100MHz). A 7D20 plug-in converts that mainframe to a 70MHz DSO.

From 7704A - TekWiki (w140.com) :
View attachment 301683
7D20 - TekWiki (w140.com)
View attachment 301684
How did you acquire those old scopes? No doubt they were used, so what precautions or checking did you do to make
sure you were not being sold bad scopes? What was the cost compared to the newer digital scopes?

Thanks
 

dl324

Joined Mar 30, 2015
16,665
How did you acquire those old scopes?
Mostly from eBay. I got a 7603 with 2 7A18 vertical amplifiers and a 7B53A time base for about $30. It would have cost close to $100 to ship, but it was from a seller within 25 miles of me, so I picked it up. I had a 7704A shipped across the country. That was my first and, with shipping, it was around $150. These scopes sold for thousands of dollars when they were new.

The 2GSa/s HP scope was also a $30 buy on eBay. No one was serious about winning the auction because it weighs a lot. It was just a 25 mile drive for me. It also came with a logic analyzer and all of the pods.
1693437212762.png
This one doesn't have the 2GSa/s scope plug-in.

When I need a logic analyzer, I use one of my 7D01's with formatter. The plug-in's are usually inexpensive. The probes would probably run $200 (for 16 channels) if you can find them. I bought up a bunch of them because they're hard to get and the logic analyzers are useless without them.

7D01 - TekWiki (w140.com)
1693437359500.png

You won't find many decent prices on eBay these days. Used test equipment prices are ridiculously high now, and have been for years now.
No doubt they were used, so what precautions or checking did you do to make
sure you were not being sold bad scopes?
I wasn't too concerned with Tek scopes. The manuals include a complete set of calibration procedures, schematics, and parts lists. The only downside is they used some custom IC's. I bought some known bad mainframes and plug-ins of unknown condition for spare parts. Luckily, I haven't had to cannibalize any of them for parts.
 
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WBahn

Joined Mar 31, 2012
29,843
What is the issue about the newer digital scopes that brings up the ease of use factor related to "data acquisition"
or other features of the newer scopes?
Or is it just about the familiarity factor you are talking about?

Thanks
I didn't say anything about ease-of-use related to data acquisition. I said that there were things you could do with analog scopes that are difficult to do with digital scopes without having to spend a lot of time and effort doing data acquisition and analysis with the digital scope. I gave the example of getting a quick (and actually pretty decent) evaluation of a circuit's linearity. On an analog scope, you can use a triangle wave form as input and then put the scope in auto-triggering mode with a fast scan rate. If the circuit is linear, you will get a uniformly intense smear across the entire screen from the lowest output level to the highest output level. If there are nonlinearities anywhere in the response, the intensity will be non-uniform and where the slope is greater or less than the average is readily apparent. You can set up and do this evaluation in a few minutes. On most (not all) digital scopes this kind of measurement is not possible, and so you have to capture input/output data and analyze it's linearity computationally.

But older scopes are, in many respects, easier to use because they are simpler and pretty uniform across manufacturers. With most digital scopes, even things that are commonplace are often buried in menu trees that are sometimes very non-intuitive.
 
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