Tektronix 7603 or 7633: Do I want one? What's a good price?

[PointyOintment]

The local government surplus place has listed a Tektronix 7603 and 7633. There's no info on them apart from those numbers (and I'm actually guessing that they're Tektronix, but I don't know of any other oscilloscope maker who used those numbers), and I haven't gone there to check them out yet, so I don't know their conditions, included plug-ins, or prices. I probably won't get to go until Tuesday afternoon at the earliest. If they're both still there then, I'll have to decide which to buy, if either.

As far as I can tell from TekWiki, the only difference is that the 7603 has a larger non-storage CRT while the 7633 has a smaller storage CRT. Storage sounds nice (and I checked to make sure it can be disabled when not needed), but I like the look of the bigger screen. Opinions? Any other differences I'm missing? Are they both bad models? What's a typical price for these? Which plug-ins should I be excited/disappointed to find in them? (I should mention that this would be my first usable scope at home, and I can't currently afford a new digital scope, so I'm hoping to get a good deal on an older one.)

[JPortici]

careful, it's a slippery slope.
double careful, you're about to get your ebay flooded with sweet plugins (see in the buy/sell section)

a dual timebase is a must, unless you don't care about seeing before/after the trigger

a 7603 + spectrum analyzer or digitizer plugin is a very sweet combination

[tggzzz]

If you have to ask, then the answer is that you don't need them.

A beginner should only buy a working scope.

The plugins are vital. There is a wide range of plugins for these scopes, some of which are very capable indeed. They are readily available on fleabay and at hamfests.

In my opinion, analogue storage scopes are a pain in the rear; digital storage is highly preferable.

In my opinion, those mainframes plus decent plugins will be suitable for many purposes, and better than a low-end digital scope for digital signal integrity measurements.

Those mainframes were top-of-the-range in their day, but they are larger than the Tek 4x5 and 24x5 series.

[cncjerry]

I have two or three of these scopes and lots of plugins.  Many of the plugins have reached the end of their service life after who knows how many years of constant use. Luckily they are so cheap you don't have to even worry about fixing them as many times the parts cost more than buying another plugin.  Many of the switches and knobs are broken beyond repair and I even went so far as to mold knobs.  That's the real issue, switches and knobs vs capacitors. And I forget, lots of burned in tubes.

And the last price I paid for a 7603 loaded with a unique volt meter plugin was $70 from Craigslist.

[edavid]

Analog storage CRTs are much dimmer than non-storage CRTs.

I would describe the 7633's CRT as dim and murky.  So, I wouldn't recommend it unless you particularly want a storage scope.

Also, these scopes tend to have low MTBF.  This is just because they have many hundreds of parts.  It's not a good idea to buy one unless you have another scope available to help fix it when it breaks.

The 7603 is a very nice scope, when it's working

[SingedFingers]

I now own 4 Tektronix 465/475's in various states of repair. If you buy one 7603 you will need another one for organ harvesting. Then you will find something that you can't get on Sphere/Qservice so you'll buy another one. Next thing you know, you're a scope collector and need to join the TEA thread.

I have resisted the 7000 series thus far as I fear my wife would have something to say. The 4xx units are easy to hide

[PaulAm]

The 7603s are pretty common and relatively cheap.  I paid $25 for a rackmount one without plugins, and around $100 for a pile of them with a basic set of plugins each.  I wouldn't pay much over $50 for one, depending on what plugins were included (and that's if I needed one, which I don't).  Of course, as alluded to above, when it breaks you'll need another scope to fix that one.

They're nice because they have the largest screen in the 7000 series.  That's useful if you find a SA or LA plugin, or even the sampling plugins, but it's also nice with the curve tracer.

I wouldn't bother with the storage one; you're much better off with a cheap DSO if you need storage.

The four bay units are a little more flexible, but they're also larger.

[tggzzz]

I now own 4 Tektronix 465/475's in various states of repair. If you buy one 7603 you will need another one for organ harvesting. Then you will find something that you can't get on Sphere/Qservice so you'll buy another one. Next thing you know, you're a scope collector and need to join the TEA thread.

I have resisted the 7000 series thus far as I fear my wife would have something to say. The 4xx units are easy to hide

Well, that's because you've only got four. You should get a sweet little blue trace 350MHz 485 to keep them company. And if you forget how to read a scale and do mental arithmetic, you'll also need a 24x5 (or two).

Of course you'll need a 464 storage scope; they are less easy to hide, since they are 6" longer.

But they are all smaller than the 7000 series.

[edavid]

They're nice because they have the largest screen in the 7000 series.  That's useful if you find a SA or LA plugin, or even the sampling plugins, but it's also nice with the curve tracer.

But it's actually nice to have a storage mainframe with the non-storage SAs, samplers, and curve tracers.  I would pick the 7613 over the 7633 though.

[David Hess]

Opinions? Any other differences I'm missing? Are they both bad models?

There is nothing wrong with either.  The 7633 is more complicated to maintain and use.

I should mention that this would be my first usable scope at home, and I can't currently afford a new digital scope, so I'm hoping to get a good deal on an older one.

You do not say where you are in Canada but my usual recommendation for beginners on a budget if they do not have help is to find an analog oscilloscope which verifiably works.  That might be a 7000 mainframe and plugins but would more likely be a 2225 or 2235 or some other portable.

Which plug-ins should I be excited/disappointed to find in them?

The typical loadout of plug-ins for these is a 7B53A timebase and a pair of 7A18 dual trace vertical amplifiers.  Sometimes 7A26s replace the 7A18s because they are a little faster and provide a very useful 20 MHz bandwidth limit function.

The unusually useful vertical amplifiers are the 100 MHz 7A13 differential comparator and the 1 MHz 10uV/div 7A22 differential amplifier.

There are too many other options to discuss without more specifics.

A dual timebase is a must, unless you don't care about seeing before/after the trigger.

No timebase will not help seeing what happens before the trigger (1); that is what the mainframe's fixed delay line is for which gives about 20ns with a slow timebase (7B53A) and 40ns with a fast timebase (7B50A) on a 7603 or 7633.

Some of the single timebases (7B50A, 7B80) support automatic peak-to-peak triggering which is a nice reason to use them if you do not need the delayed timebase.

The 7B53A annoyingly only supports mixed sweep.  If you want alternate sweep, then use a 7B92A.

If you have to ask, then the answer is that you don't need them.

A beginner should only buy a working scope.

I agree.  See below.

I have two or three of these scopes and lots of plugins.  Many of the plugins have reached the end of their service life after who knows how many years of constant use. Luckily they are so cheap you don't have to even worry about fixing them as many times the parts cost more than buying another plugin.  Many of the switches and knobs are broken beyond repair and I even went so far as to mold knobs.  That's the real issue, switches and knobs vs capacitors. And I forget, lots of burned in tubes.

They are great oscilloscopes but be prepared to do significant maintenance including calibration and possibly a complete rebuild.

These mainframes are especially worth the trouble if you have a use for the more specialized vertical amplifiers like the differential 7A13 and 7A22.

And the last price I paid for a 7603 loaded with a unique volt meter plugin was $70 from Craigslist.

Somehow even without looking to, I have ended up with two perfectly working 7D13 multimeters.  I do not have much use for them but wow their function control has an awesome feel.

Analog storage CRTs are much dimmer than non-storage CRTs.

I would describe the 7633's CRT as dim and murky.  So, I wouldn't recommend it unless you particularly want a storage scope.

The 7603 was not the brightest or sharpest to start with so the 7633 is not bad compared to one of the really bright and sharp CRTs like the 7704A or 7904.  My 7834 storage mainframe seems about as bright and clear as my 7603 but my 7904 puts them both and every other oscilloscope I have to shame.

Also, these scopes tend to have low MTBF.  This is just because they have many hundreds of parts.  It's not a good idea to buy one unless you have another scope available to help fix it when it breaks.

Luckily most of the part failures are common ones and not the custom ones and the custom parts are not that difficult to find.

Another working oscilloscope is a good idea for maintaining these.

But it's actually nice to have a storage mainframe with the non-storage SAs, samplers, and curve tracers.  I would pick the 7613 over the 7633 though.

I was wondering which would look best with my 7CT1N and sampling plug-ins so I asked about this over on the TekScopes@yahoogroups.com email list and the consensus was that the 7633 storage display looks as good as the 7613 storage display.

[SingedFingers]

I now own 4 Tektronix 465/475's in various states of repair. If you buy one 7603 you will need another one for organ harvesting. Then you will find something that you can't get on Sphere/Qservice so you'll buy another one. Next thing you know, you're a scope collector and need to join the TEA thread.

I have resisted the 7000 series thus far as I fear my wife would have something to say. The 4xx units are easy to hide

Well, that's because you've only got four. You should get a sweet little blue trace 350MHz 485 to keep them company. And if you forget how to read a scale and do mental arithmetic, you'll also need a 24x5 (or two).

Of course you'll need a 464 storage scope; they are less easy to hide, since they are 6" longer.

But they are all smaller than the 7000 series.

I really want a 485 but they seem to go for stupid money. I am staying away from storage scopes. The digital ones are, well, digital. The analogue ones are generally circling the drain. Every time you use one you're shoving it slowly towards the edge of a cliff.

[tggzzz]

I now own 4 Tektronix 465/475's in various states of repair. If you buy one 7603 you will need another one for organ harvesting. Then you will find something that you can't get on Sphere/Qservice so you'll buy another one. Next thing you know, you're a scope collector and need to join the TEA thread.

I have resisted the 7000 series thus far as I fear my wife would have something to say. The 4xx units are easy to hide

Well, that's because you've only got four. You should get a sweet little blue trace 350MHz 485 to keep them company. And if you forget how to read a scale and do mental arithmetic, you'll also need a 24x5 (or two).

Of course you'll need a 464 storage scope; they are less easy to hide, since they are 6" longer.

But they are all smaller than the 7000 series.

I really want a 485 but they seem to go for stupid money. I am staying away from storage scopes. The digital ones are, well, digital. The analogue ones are generally circling the drain. Every time you use one you're shoving it slowly towards the edge of a cliff.

485s go for very sensible prices

Analogue storage scopes were only used because they were the best thing available for capturing nonrepetitive transients Apart from that they always were a pain in the posterior.

Oops, I mean 464s are a wonderful 100MHz scope with storage, and I'm sure you would like to purchase the one I got for the grand sum of £0.

[David Hess]

I am staying away from storage scopes. The digital ones are, well, digital. The analogue ones are generally circling the drain. Every time you use one you're shoving it slowly towards the edge of a cliff.

Storage CRTs are more sensitive to damage but as far as I know, they do not degrade with use unless abused which admittedly is easy to do.  MCP CRTs on the other hand wear out with any use.

Analogue storage scopes were only used because they were the best thing available for capturing nonrepetitive transients Apart from that they always were a pain in the posterior.

Dedicated variable persistence and bistable CRTs are easy enough to use.  The multimode oscilloscopes like the 7834 are best used in only variable persistence mode though; anything else is annoying or even dangerous.

Oops, I mean 464s are a wonderful 100MHz scope with storage, and I'm sure you would like to purchase the one I got for the grand sum of £0.

I have to admit, I did not like the 464 that I used long ago but I love my current 7834.  On the TekScopes@yahoogroups.com email list we had a discussion about what were the most essential 7000 mainframes and I said my first choice would be a 7834 or 7934.

[PointyOintment]

A beginner should only buy a working scope.

I should mention that this would be my first usable scope at home, and I can't currently afford a new digital scope, so I'm hoping to get a good deal on an older one.

You do not say where you are in Canada but my usual recommendation for beginners on a budget if they do not have help is to find an analog oscilloscope which verifiably works.  That might be a 7000 mainframe and plugins but would more likely be a 2225 or 2235 or some other portable.

[…]

Another working oscilloscope is a good idea for maintaining these.

I should have explained what I meant by "it would be my first scope at home". At my hackerspace we have a 2465A and a 2225 (and a couple of other basic scopes), so I'm not new to analog oscilloscopes, and I could take mine there to use those to work on it if necessary. But I'm not there all the time (despite what other members may think ) so I want one at home.

Regarding broken switches and knobs, thanks for telling me. I'll be sure to check those. Would it be a good idea to plug them in and check functionality and screen burn before buying, or would it be better to not test them and leave them unpowered until I get one home and can bring it up slowly with a variac (and risk buying something that needs more work)? (I don't yet know how recently they were removed from service—I'll look for cal tags when I check them out. Also, some other prospective buyer might have plugged them in before I get there.)

[David Hess]

I should have explained what I meant by "it would be my first scope at home". At my hackerspace we have a 2465A and a 2225 (and a couple of other basic scopes), so I'm not new to analog oscilloscopes, and I could take mine there to use those to work on it if necessary. But I'm not there all the time (despite what other members may think ) so I want one at home.

A rebuilt 7603 or 7633 would make you the talk of the hackers.  Refurbishing one would be a learning experience.

Regarding broken switches and knobs, thanks for telling me. I'll be sure to check those. Would it be a good idea to plug them in and check functionality and screen burn before buying, or would it be better to not test them and leave them unpowered until I get one home and can bring it up slowly with a variac (and risk buying something that needs more work)? (I don't yet know how recently they were removed from service—I'll look for cal tags when I check them out. Also, some other prospective buyer might have plugged them in before I get there.)

Check that the timebase knobs engage their detents.  For a dual timebase, check both by pulling the control straight out.  If they do not then it may not be fatal but it can be a difficult repair.  Timebases are easy to come by though.

The 7603 and 7633 use a linear power supply.  The regulators are well protected so I like to test new plugins in my 7603.  I would not bother to power it up with a variac but it will do no harm.

The 7603 may or may not have a fan and the 7633 always has a fan.  They tend to be very reliable and quiet.

Common problems include:

1. Shorted solid tantalum capacitors in the plug-ins.
2. Worn out aluminum electrolytic capacitors in the power supply of course.  This might not be apparent in the output capacitors so I would just change those.
3. Sticky pushbutton switches.
4. Dirty potentiometers.
5. Sometimes the TO-3 pass transistors in the regulators which are rigidly mounted crack their printed circuit board joints.
6. Texas Instruments edge wipe sockets are terrible.  You may need to reseat ICs or even replace sockets.

[PointyOintment]

I went and checked them out yesterday. I doubt anybody else will buy them soon, because they're $80 each and both malfunctioning. (They're a bit longer than I expected, too—they won't fit on the shelf I was thinking of.)

The 7603 has a 7B53A, a 7A18, and 7A18N. The 7633 has a 7B53A and two 7A18s. The 7603's slope knob is a bit loose on the shaft, and its right amp's CH2 V/div knob has half of itself missing but still works fine. The 7633's time/div knob has a bent shaft, resulting in it not pulling out (or being always pulled—not sure) and its secondary knob turning with it (stuck). Otherwise, the controls work perfectly (mechanically at least).

I pulled out the plug-ins and inspected them visually. They're clean and look good inside. I didn't look inside the mainframes but I assume they're in similar condition. There were no cal tags that I noticed, though I was pretty tired (awake for over 24 hours at that point) so I might have overlooked them.

I took them over to a table near the outlet where everybody tests stuff and plugged them in. On the 7603 I got nothing onscreen no matter what I did with the controls. The power light did come on, though. On the 7633 I got a strange flashing blobby pattern on the screen that changed a bit depending on storage mode, but no other controls did anything to what I saw on the screen. See video below. Again, the power light worked, and so did the reduced scan light.

https://youtu.be/wrgd1IW4jzo

I might be going back soon for some other items (Friday maybe) and can try opening them up and checking voltages then.

It turned out later that another hackerspace member, who isn't a member here but should be, had been there earlier in the day and tested both of these scopes too, with the same result (and the same disappointment with the slightly high price). He didn't have any insight into the problems with them, nor did another member whom I showed the video of the 7633. (But he did get a couple of GenRad 5-decade resistance boxes and an Avometer—literally a second or two after they were put out for sale—for $10 each! I'd seen them listed on the website earlier and was somewhat disappointed to not find them when I visited, but I'm happy they went to a good home.)

[EV]

In the scope 7603 the timebase 7B53A is in the wrong slot. It must be in the slot 3 which is most right.

[David Hess]

In the scope 7603 the timebase 7B53A is in the wrong slot. It must be in the slot 3 which is most right.

That would not stop it from operating.  Any vertical amplifier or timebase in the right most slot will unblank the CRT.  Timebases can be used in the vertical slots to generate rasters and vertical amplifiers can be used in the right most slot for X-Y displays.