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Tuesday, August 22, 2017

DIY build of the Tektronix 5CT1 Curve Tracer

When I worked at Tektronix in the 70's, I build my own 5440 Oscilloscope and TM503 mainframe.

What that means is that I collected every part and soldered each one of them myself. Some boards came from scrapped units, so I also scavenged parts.

This in itself was not a very unusual project at Tek, but I believe I was the only one at the time to build a 5440. Several others build portable scopes, but since I repaired the 5000's, I was very familiar with them. I purchased many parts from the Tek factory in Heerenveen, and in the employee shop in Beaverton. Some very good friends at Tek helped me to get the printed circuit boards, and several special hardware items, which were otherwise not available. I remember that one time I went on a business trip to Beaverton with one suitcase, and came back with two. Imagine the explanations I would have to do at customs at Schiphol...if I was stopped. The CRT was a reject from a customer (there was a dust spectacle on one of the plates that caused a funny light reflection effect. A colleague of mine spend days ticking on it and shaking the tube to get it off the plates. Eventually he gave up, and it was decided to scrap it. So, I had my tube. When I build my scope, I never saw that effect again... go figure)

I took the transformer from a unit that had been on fire, so that was another item I got. One of the 5000 frames was bent when a customer dropped his unit. I replaced the frame, and was lucky to be able to bent the old one in shape again without breaking it. It is now my TM503 frame.

The list goes on and all in all it took me several years, but here it is:

The measurement system consisted of the following parts:

Tektronix 5440 Plugin Oscilloscope System.

D40 Single Beam Display Unit
5403 3-slot Mainframe with Display Readout Option
mainframe is typically 70MHz, could display up to 100MHz.

5A48 Dual Channel Amplifier with 50Mhz bandwidth

5B42 Delaying Timebase, to zoom in on a specific area of the trace.

5A22N Differential Amplifier (down to 10microVolt), with LF & HF filters and DC offset.

TM503 Mainframe
This is a TM503 with original parts, but build in a 5100 lower section scope frame.
It has no middle section, and therefore no handle. I usually have the scope on top of the TM503, so I don't miss the handle.
One the left:
DM502 Digital Multimeter, VAC, VDC, ACmA, DCmA, Ohms, Temperature(C/F), comes with 2 temperature probes and a spare tip
In the middle:
PS503A Dual Power Supply, (0 +20V, 0 -20V with tracking, 0-400mA and fixed 5V 1A)
This is a self-build copy of the original unit with lots of original Tek parts.

To the right:
SG502 RC Oscilator, 5Hz to 500KHz low distortion (<0.0035%) sine wave and square wave output
This is a fantastic unit for audio work, which is what I did most of the time, back then.


5CT1 Curve Tracer
After I left Tek, I had no time do spend on my electronic hobby, so everything was mostly stored, and followed along with the several moves we've made. Somewhere around 2000, I wanted to finish an instrument that was on my to-do list for quite some time, a Curve Tracer. Some parts were still waiting for this project, but since I left Tek, I had no access to parts anymore, at least not for reasonable prices.

I had no access to a front panel either, so I made my own, but missed the engravings for the settings. I also didn't have the customary drum rotary switch that Tek uses a lot, so I used normal single deck rotary switches. These were connected through diode matrices that drove little 5VDC DIP relays, and these mimicked the finger switches. I used the same technique to add a read-out capability for the Vertical Amperes/Div. and for the Step Amplitude. The ./. 1000 switch was added to the mix, so the display also changed from milli to micro etc.

The instrument uses a transformer to obtain voltages up to 300V. At first I used a normal 220V transformer in reverse, but I was not too happy about that. This transformer had no shielding either, so I got some extra switching noise. When I had an opportunity, I had a special transformer made. There was no information about the transformer Tek used, so I had to do some reverse engineering and the transformer company did the rest. In the end this trick worked really well and the unit is within specifications.

This is how it looks like (left compartment):
Note that since I added the readout capability at a later date, I should have renamed the 5CT1N to 5CT1. The "N" suffix in Tek parlor means "No Readout".

BTW, in case you wondered, the 7CT1N is exactly the same unit, but has a mainframe adapter board to make the circuit fit in the 7000 mainframes.

 Here I'm measuring the voltage drop of a 1N914 diode, showing 0.7V (at .5V/Div)

This is the breakdown voltage of the 1N914 at 20V/Div 

This is the voltage drop of a Schottkey diode.

Here is a trace of a 12V Zener diode (at 2V/Div)

This is the characteristic of a 2N2219 transistor.

This is the breakdown voltage of the 2N2219 at 20V/Div.
Note that the traces show in different intensity, but is caused by the sweep rate of the scope and the way I took the picture.

This is a screen shot of a tunnel diode, used quite a bit by the Tek designers in the 60's and 70's.

This is a BS170 MOSFET

Right now, I'm selling all my Tek equipment and parts. I don't have the space to keep them on my bench, and it's too cumbersome to create the needed space to use them for measurements. I have a new scope now, and I have no need for the DM501 and the PS503 anymore.

I will miss the SG502 because of the good quality sine wave forms (0.0035% THD). I may rebuild that instrument in a different enclosure at a later date, maybe with OpAmps. (one more item added to the already long Bucket List)
Update, I just finished that project, look for it on my blog.

And I will also miss the 5A22N differential amplifier capabilities and the Curve Tracer, although I'm using less and less older parts that need checking or verification. Parts are so inexpensive these days that swapping them out is a no brainer, certainly compared to the old days.

I also started a project to replace the 5CT1/7CT1 Curve Tracer

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