Tektronix 545B Oscilloscope with 2 additional units

[TheFlash]

Newbie member here, what a great resource this forum is.

Just before the very first lockdown, I went to an auction viewing to check out some speakers and ... well, you know what happens when you wander round an auction viewing "just looking". I ended up buying 2 oscilloscopes and an oscillator, based on nostalgic ideas about "proper" (ie. pre-digital) electronics. The 545B was one of my acquisitions.
I have done nothing with it. By a far more knowledgeable friend, I was warned off simply reseating the valves, plugging it in and having a play! I do now have a variable voltage supply but have never got around to using it as I still work full time ... and it appears fiendishly complicated.

Basically, I'm out of my depth by quite a margin, though my fascination remains.

I'm stuggling to see how to share an image but will work it out...

I would appreciate any advice, any pointers to people who understand these things, regarding getting it checked over... or frankly, whether it has any value which justifies getting it sorted to move it on. I did see a refurbished one had gone for multi-hundreds of pounds but this is far from being refurbished...

[kalee20]

It's a good scope, highly useful. Having sweep outputs available on terminals on the front is something not often used, but when they are, it's super.

I'd certainly start by keeping it in a dry room for at least a month, while others comment - I'm not so familiar with the circuit to be able to advise straight off!

[barrymagrec]

One thing to remember - don`t operate it without a plug in unit installed, a resistor is likely to burn out.

The 545B is a much better scope than the 545A, it has much more usable screen area.

If you have to fault find the PSU the -150 volt supply is the reference for all the others.

[factory]

Hopefully there should still be a small amount of the tin/lead/silver solder inside, for use with the tag strips to prevent the silver plating from being dissolved by the solder.

David

[TheFlash]

Thanks for swift replies, everyone!

I'd love to get this up and running myself, hugely satisfying, but the combination of time and skills (not) make this all but impossible.

If I get chance during the week, I'll put up a similar post about my Marconi TF2202 and Wien oscillator!

[Radio Wrangler]

There are rather high voltages in there and they cn be damaged by trying to use them unless they are fully dry. A dry room for a month is a very good idea.

The plug-in modules are the early stages of the amplifier which deflects the spot in the up/down direction.

The module plugged in is the general purpose dual channel one and will put two traces on the screen so you can monitor two different places in whatever you're testing.

Top left is the general purpose single trace plug-in. Top right is a more specialist type which can handle differential signals and is much more sensitive than the general purpose ones. But the frequency response is more limited.

However, it is the timebase, the section which sweeps the spot across the screen to give the time scale and to draw out the graph of the varying signal voltage, which is the star of the show.

This is an oscilloscope for analysing repetitive signals. Set up right it will keep drawing the same picture, so refreshing what you see. If it's used to view a one-off event, you get one trace and it fades away quickly, and that's your lot. Doing repetitive re-writing of the same picture, it's important to start the timebase scanning when the waveform is at the same point each time, otherwise you get a rolling of confused picture.

This was the achilles' heel of earlier scopes. They had controls for you to try to synchronise them, but they were rather uncertain and it was difficult to get a stable picture. Changes in the waveform could upset it as well.

The founder of Tektronix invented something called the Triggered Timebase. The circuit diagrams of these things are a lot more involved than the crude ones before. But there are two buts! The first one is that unlike the older timebase schemes, the triggered type works properly and can be made to do things in an understandable way. Secondly, although there is more circuitry, it is broken up into understandable blocks, each with a single purpose. There is more of it, but it's still a lot more understandable.

The founder first thought of marketing his invention to existing test equipment firms, but they were busy on government contracts, but they advised him to set up his own firm, as they had done some years earlier. These were gentler times. Tektronix with their triggered timebase was a game-changer and set the style of oscilloscopes for decades to come. Your 545 drives just like the last generation of analogue scopes, and has set the operational style which the digital oscilloscopes try to emulate.

Your scope doesn't just have a triggered timebase, it has two for the time being, you need to first learn how to drive it using just the main timebase with the controls for the delayed timebase parked in positions which don't intrude. The second 'delayed' timebase comes into its own when you need to winkle details out of complex waveforms like television or radar ones. With it you can greatly expand the time scale of the picture and scroll through it with that knob with the silver turns-counting scale.

Triggered timbases confuse any people because they have a natural, long-term condition of not running at all. They will sit there, holding the spot at the left edge of the screen, with it darkened into invisibility. It is sitting there waiting to be triggered.

Enter the trigger circuit. It is given a sample of the signal voltage and it compares it against the voltage from a pot on the front panel, 'Trigger level'. It looks for when the signal voltage crosses the trigger level voltage, and it's sensitive to the direction it's moving in. When it sees the selected circumstances, it signals the timebase that it may start its run now.

This means that successive re-runs on the repetitive signal start in the same place, at the same point on the waveform. You get a nice stable picture.

There is a disadvantage. If the trigger controls aren't somewhere near right for the signal, the timebase is never triggered and the CRT sits there, dark, giving you no clues. You'll find a switch somewhere labelled Normal and Auto. Normal is what gives you the dark screen if not triggering. Select auto and a little timer says that if the timebase hasn't run for a while, it had better just run to give you some clues. With a signal that triggers infrequently, these auto runs can be a problem, so the norm position of the switch turns off the auto-runs.

So, it's a great scope, and one of a family that set the direction for oscilloscopes right to today. In its day it had formula-1 performance and Rolls-Royce build quality. And the price of both together

Learn from it and enjoy it. It's still a capable machine for doing plenty of things today.

David

[TheFlash]

Some great posts here... an especially HUGE thank you to Radio Wrangler for the amazing insights into its capabilities. Just awesome.

[Craig Sawyers]

The 545B was introduced in 1964, and cost $1,650 without plugins.

There were more expensive units. The 555 was $2,650!

Craig

[TonyDuell]

Yes, but the 555 is almost a double 'scope. OK, one CRT but with 2 electron guns each with its own X and Y plates. Two EHT power supplies. 2 timebases/X amplifiers. 2 Y amplifiers.

I see the OP has a dual-trace plugin (in the 'scope in the photo). This works like a more modern dual-trace 'scope, it switches the single beam in the CRT between the 2 inputs. It's useful unit. The 'type L' is a fairly basic single-trace plug-in, useful for testing the 'scope as it's simple-ish inside but less useful for using the thing. I can't remember what the other plug-in is for.

[Diabolical Artificer]

First off download the manual off line, then leave in a warm dry place for a week or so, the scope that is not the PDF. Whilst your doing that inspect it visually. There are three access panels, two on the sides, one on the bottom. Start with taking off the side panels then inspect the valves, you'll probably find quite a few white ones, these are dead and must be replaced. BTW some valves are hiding in out of the way places.

The next bit needs a high voltage source and meters + soldering iron.Take off the bottom access panel, you'll see loads of big electrolytic capacitors, each one needs testing for leakage. Some cans have two capacitors in them and need reverse voltage applied.

If all is well there, power it up. You can't really start these on lamp limiters or a variac as they need a lot of power for the heaters, pointless current limiting. Next check power supply rails. On the RHS there is a single ceramic wafer towards the back, this has all the rails brought out to it, +500v, + 350v etc are marked on it. The -150v is the reference that all other supplys refer too and must be pretty spot on.

If you have a trace, brilliant, if not you'll need to check the EHT. There's over 2500v in there which needs caution and a special probe.

Your scope might need a lot of work, or it might work first time. If you have some electronics knowledge and experience it's possible to muddle through and fix these. If you have zero knowledge your going to struggle.If you get stuck I'm not far away from you, drop me a PM if you need me.

Andy.

[TheFlash]

Originally Posted by Diabolical Artificer

.

There's over 2500v in there which needs caution and a special probe.

Your scope might need a lot of work, or it might work first time. If you have some electronics knowledge and experience it's possible to muddle through and fix these. If you have zero knowledge your going to struggle.If you get stuck I'm not far away from you, drop me a PM if you need me.

Andy.

Cheers Andy.

I've extracted a couple of quotes which suggest I'm WAY out of my depth, both in terms of technical knowledge and skills and in terms of access to the right supplementary equipment.
I might need to look myself in the eyes in the mirror and move this on, though I know its value will be limited if its condition is unknown...
PM noted, thanks again.

[Radio Wrangler]

You could treat it as a learning opportunity... rather a large one. But remember, everyone was born with no knowledge. It can be acquired, if you want.

David

[Craig Sawyers]

Two things to watch out for. First is the little potted HT transformer. Tek decided to stop wax potting these (which worked fine) and convert to epoxy potting. That worked fine for a few decades, but progressively degrades. You'll know if you have this problem because after maybe ten minutes the traces fade out.

There is no solution to that other than a rewound transformer. Chuck Harris on Tekscopes used to do these, and may be worth contacting if you have this problem.

The 576 curve tracer had the same problem. On later units Tek replaced the epoxy potting with silicone potting, which also cures the problem.

The other thing to beware is that it uses tunnel diode triggering. Be very very careful if you are probing signals that you don't blow one up. Although Leo Esaki won the Nobel prize essentially for the Tunnel Diode, they have been obsolete for decades. Blow one up and weep. Also never test a tunnel diode on a DVM or other meter - again because you could blow it up. The only way of testing these is with a curve tracer, and again with real care.

Good luck

Craig

[Craig Sawyers]

There is a simple tunnel diode curve tracer here, pages 66 to 71

https://w140.com/Ge1961TunnelDiodeManual.pdf

Note that you need an oscilloscope too! That gives the fundamental rabbit hole: how many oscilloscopes do you need? Answer: always one more.

The GE book in general is an excellent reference on Tunnel diodes, published at the height of their use in 1961.

Craig

[Radio1950]

Tek 545B.
The CRO of choice for discerning Radar techs.
High trace brightness and excellent trigger for A del by B means you could inspect a 2uS signal at 1000uS from radar sync.
We kept these CROs long after solid state HP76xx etc were available.

[cmjones01]

Your 545B is a great scope, as others here have said. In spite of its age and size it's still very capable today. I have its close relative, the 535A, which is basically the same but with only 15MHz bandwidth. During last year's lockdowns I was working from home and pressed the 535A in to service as my "daily driver" scope for professional use. Once you've learned how to drive it, a good analogue scope will reveal all sort of things. I was surprised to find that the humble 15MHz scope was able to show something of a 1.2Gb/s digital data stream, enough for me to identify whether it was working or not, which is pretty good going considering the signal exceeded the scope's bandwidth by a factor of 80! No modern digital scope will give you such latitude, but the Tek's excellent design and pin-sharp CRT reveal a lot. Getting the most from it is like playing a musical instrument.

If it were mine, I'd make sure it's dry and there's nothing obviously missing or damaged. Then give the fan a spin with a finger to make sure it rotates freely and doesn't clatter against anything (that's really unnerving when you switch on for the first time). Then switch on and see what happens. Fan should spin, power light and graticule lights should come on, then about 45 seconds later there should be a click as the main HT relay pulls in and various other indicators should light up. A bit of twiddling of the controls should get you a trace. The 545B doesn't have any failure-prone metal rectifiers, and the electrolytic capacitors they used are good quality and don't tend to fail.

As Craig has said, the late 500 series instruments do suffer from failing high voltage transformers. I had a 549 which had had a new transformer wound and fitted at some point in its history, so you may be lucky and find that yours has been done. Otherwise it'll probably work for 15-20 mins and then go dark.

Once you have it working, be careful not to go down the rabbit hole of trying to find all the useful plugins! Your 1A1 dual trace plugin is probably the most useful in day-to-day work and the type D differential amplifier can be handy for some jobs.

Chris

[TheFlash]

Thanks again, everyone.

I visited Andy [Diabolical Artificer] today with both my 'scopes and my Wien bridge oscillator. He managed to get all of them to do something which was fantastic to see. You can read all the manuals and watch all the vids you like, but nothing beats meeting an actual expert in 3D.

Story to be continued but I thought you might like to see both scopes doing that thing scopes do:

[Diabolical Artificer]

Yes, we got everything working ish. After a visual inspection and finding all valves looking ok, first tried the 545B with the 1A1 plugin, brought it up on a variac LL and we got a trace but no vertical adjustment. Would have checked all caps but pushed for time.

Next tried the type D plugin, success,up/down adjustment then a frantic search for cables and connectors to connect my Advance 81A sig gen which has balanced out, result is what you see in post #17. Couldn't quite get everything stable for a stable trace but essentially everything's pretty good.

The CRT is very different to my 585A which is a lot lighter, both have scale illumination lamps out but the 545B display looks very dark in comparison. At some point I'll check what CRT is fitted and do a lot more checks and cleaning of switch's.

Whilst F was getting the Marconi TF2202 from the car I checked the AEI sig gen. It's a very early Wein bridge oscillator with that typical boingy trace when adjusted. Pots & SW's need a good clean which should be fun as some of them are sealed. Someone had made a crude battery eliminator & the last battery fitted had leaked causing severe corrosion.

Lastly brought the Marconi up slowly on a variac after a visual inspection and got traces but switched it off pretty quick as there's a high speed whistling. Thread started separately for this scope.

So, all in all a good morning and before F left he kindly gave me the 545B & plugins, which was very kind. I've to fix the other scope and sig gen and if in the future I get one of my other 545B's going, pass it on potentially.

So another really nice chap met via the forum, was very happy to help a beginner and pass on the little I know about these old Tek 500 series scopes. We do need some younger lads and lasses getting interested in this vintage kit though so that they will be preserved and kept running into the future, if there is one.

Andy.

[cmjones01]

The trace on the 545B won't stabilise because you have it set in "line" trigger mode so it's synchronised to the mains, not your signal source. Set trigger to "int" and things should improve.

Chris

[Diabolical Artificer]

Thanks Chris, I did try other trigger settings with no improvement, as mentioned this was only a quick startup, it needs TLC.

Andy.