Oscilloscopes

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Since I own a few oscilloscopes now, I’d thought I should add a webpage about them. I knew it was time to get an oscilloscope when I needed to know certain frequencies for proper operation of my nixie clock. Most of the scopes here were bought locally from craigslist mainly because I can check it out in person and save on shipping. I’d suggest you do the same if you are looking for one. The scopes here were had for under $100 but keep in mind that these are very old instruments. Their date ranges from the early 60’s to the late 80’s. I am also a member of Tekscopes on Yahoo Groups. It's a good place to get information on servicing and repairing scopes. Links to free pdf manuals are here.

 

Basic Principal

An oscilloscope is an electronic test instrument used to observe electronic waveforms that are displayed on a graph that has voltage (vertical axis) plotted as a function of time (horizontal axis).  They are used to troubleshoot problems, find frequencies, rise time, period, and other time measurements. Since scopes have calibrated timebases and voltage attenuators, you are able to make accurate measurements that are related to time and voltage.

 

 

Tektronix 310A

This tubed scope was made in the early 60's and was their smallest, most compact model at the time. I only had to replace 2 tubes and I haven't had any others go bad yet. It works great for being so old! Since the top, bottom, and side panels are perforated, no fan is needed! As expected, it gets really hot after being on for more than 10 minutes. The scope has a hinge in the back that allows you to open it up to service it. Tek obviously put in some engineering into the serviceability and user friendliness of this scope. I think it's pretty cool that something this old still works perfectly. Keep in mind that this was made before transistors were used in computers.

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Tektronix 515A

The 515A is a tubed scope that first started being manufactured during the 50's. It has a 5in CRT and a bandwidth of 15Mhz. I believe this scope was made in 1962 because all of the tubes have a 62 date code on them (unless all of the tubes were replaced at that time... not likely). I also found this one on craigslist. Supposedly it came from a grandfather and the couple I bought it from didn't have a clue what it was. It's in very good condition, no dents in the chassis or scratches on the graticule, just very dusty inside and out. It displayed a square wave when I tested it before buying! I mainly bought it to clean, restore and calibrate it. As you can see, it cleaned up very nicely (before and after pictures are in the 515A gallery)! I used 91% isopropyl alcohol in a spray bottle to wash the insides and I made sure to avoid the transformers! The front panel and covers were cleaned with a simple green type cleaner. The knobs were hand washed and scrubbed with a toothbrush. After cleaning, one tube decided to die but after replacing it, everything works great (not too bad... only 1 out of 32)! The trace is extremely sharp. The 310A & 515A have the sharpest traces of all of my other scopes. The scope is now calibrated within spec.

 

515A Picture Gallery

 

Tektronix 7603 Mainframe

This is a Tektronix 7603 100Mhz mainframe with the following plugins: 7A18 75Mhz dual trace vertical amplifier, 7CT1N Transistor Curve Tracer and 7B53A 100Mhz dual delaying time base. I got the mainframe specifically for the 7CT1N plugin so that I could test transistors, FETs and diodes. The curve tracer displays the characteristics of the DUT on a voltage (x) vs. current (y) graph. The 7CT1N is good for testing low power transistors and could provide up to 240ma collector current @ 7.5v and 6ma collector current @ 300v. The x-axis is collector/drain volts (Vce), y-axis is collector current (Ic) and the step is base current (Ib).

 

Below is a family of curves from a 2N3904 NPN Transistor: Ic 2ma/div, Vce 2v/div and Ib 20ua/step. For an example on how to interpret the curves: The second curve from the top shows that the transistor provides Vce 12v @ Ic 13.6ma when provided with a base current of 80ua. Note that the starting voltage is 20v (Vce) with no base current and that when more current is fed into the base, the more current is sunk through the collector but Vce has dropped to 12v. This shows the transistor acting as a current regulator.

 

Same transistor as above but ranges changed: Ic .5ma/div, Vc 5v/div and Ib 2ua/step. The photo below shows that the transistor Vce will only go up to about 50v with Ic >4ma. It will continue to operate at about Vce 50v until its current limit is reached.

 

 

 

 

Tektronix 453

This is a 50Mhz transistorized analog scope made in the early 70's.

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Tektronix 475A DM44

This is a 250 Mhz transistorized analog scope that was made sometime in the 70's. This one is still my favorite one to use out of all of my scopes! I found the DM44 really useful. It's a multifunction meter that measures voltage, resistance, temperature, and delta time. Definitely try to get a scope that has one added on. This is a great scope for beginners and hobbyists. When I first bought this scope, channel 1 wasn't working, hence the low price. I opened it up and reseated several socketed transistors and ICs on the Vertical Amp circuit board. Turned it back on and it works fine! Also, I had an issue on both channels (not at the same time) that any setting with a 5 in it wasn't working (just shows a line) but any other setting would work fine. I fixed it by reseating the socketed resistors in the voltage attenuators (a metal shield must be removed first). The lesson here is to reseat ICs and transistors if you have any small problems like that. This should also help if you are working on a tubed scope that's having minor issues.

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Tektronix 2247A

This is a 100 Mhz digital/analog scope. What's nice about this scope is that you can pick from a menu what kind of measurements you would like to make. Here are just a few: peak to peak volts, gated voltage, frequency, risetime, and gated frequency. Since it's digital, it is extremely accurate compaired to the analog scopes. There are also voltage and time cursors that track the top and bottom (or sides) of a waveform to continually provide measurements. It is also possible to manually move the cursors to measure other parts of the waveform. It's also nice that you can view both A (intens by B) and B (delayed sweep) at the same time... it is not possible to do that on the 475A or 310A. The 2247A actually has two 8-bit cpu's... one that controls measuring and calculating and the other that only controls the readout on the screen. I also copied the eprom that contains the firmware for backup purposes. It can be downloaded here.

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Handheld Scope

This is a handheld scope by Velleman. I believe it has a bandwidth of 3Mhz. This was donated from Ken (thanks).

 

 

Last updated May 2010

Contact: Tai Oliphant

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