Tektronix 160 Series

[Mark Hennessy]

Steady on Mark, it's a 7704A. Even with the 7A18s it's good for 75MHz. I could get my 475 and Sunday-best Probes out if pressed. That's good for 200MHz.

LOL

The best I can do is 100MHz, but my everyday 'scope is a 20MHz Telequipment. I'm an audio person, so I'm far more interested in dynamic range than bandwidth!

My TQ has a differential plugin that goes down to 50uV/div. Only 2MHz, but that's fair enough. For chasing earth loops and other weird low-level audio stuff, it's absolutely invaluable. No-doubt Tek offered similar plugins. I've also seen the 2225 which goes down to 500uV...

Still, it's looking good. I enjoyed the schematics - as I'm increasingly finding with the valved Tek designs - because they are almost identical to the transistor designs I'm familiar with. Basically, keep the topology, but replace with transistors and reduce the voltages a bit. Seems to work

[ppppenguin]

Regarding fuzzy trace, are you looking at trigger jitter or astigmatism? Or even simple lack of focus? Some scopes are sharper than others. You could cut yourself on the trace of my 547. The much later 24xx series are nothing like as sharp though still more than good enough for all purposes.

Of course, the 547 is a 50MHz 'scope, and some of those 24-series 'scopes were 200, 300 or 400MHz. What looks like softness is sometimes noise - engaging the BW-limit mode confirms that. Even my humble 100MHz Fluke Combiscope is slightly fuzzy when not in 20MHz BWL mode.

And let's not get into the whole "digital 'scopes are noisier than analogue 'scope" debate

But yes, there are many variables...

Of course there's noise when at full BW. I'm talking about with the 20MHz filter switched in. The fundamental electron optics just aren't as sharp as on the 547. Shorter CRT? More compormises due to wide BW? Higher PDA?

One day I might get myself a nice digital scope, one that can do a decent job of displaying video. Will need digital phosphor or equivalent. My TDS210 and all simpler DSOs do a horrible job on video.

[Mark Hennessy]

Ah, but not everyone has our wisdom. That's a diplomatic way to say that we've been doing this a long time

Some of our trainees are quite upset when they see a high BW 'scope because they've come through university using basic 20MHz models for everyday experiments and wouldn't necessarily consider the noise question. To be honest, whatever 'scope manufacturers might say, I bet that is one motivation for including the 20MHz mode. Personally, I'd label it "SET FOCUS"

Our 2400-series 'scopes have had relatively little use, and they are still pretty sharp. Just a couple of weeks back, I was comparing them to a well-worn example that we rescued from TVC, and that has been really hammered over the years. Still usable, but definitely a bit soft. Probably the sharpest 'scopes I've seen are the various Philips models - PM3055 and onwards, with high PDA and sorted electronics (all-electronic with just a few reed relays here and there). My later Combiscope also fits that category - very nice indeed. Our 7000-series model is as soft as anything, but that is a storage model if that makes any difference? My DM63 is also a storage 'scope, but is also sharp - but doesn't go as bright as the Philips. Clearly, there's a lot of art that goes into the design of the CRTs - quite how they work at the write speeds they do is beyond me.

I finally took the plunge and brought a Rigol DS1054Z. Annoyingly, the price has fallen by 20 quid since I bought it. I plan to start a thread in a couple of weeks time, but first impressions are very good indeed. Analogue video looks especially good - although I'm no expert on video. For single-shot stuff, it's amazing - the extent to which you can pan and zoom the acquired trace really impressed me - it'll be excellent for doing digital stuff. More later...

[ppppenguin]

There are some very nice looking scopes in that Rigol range. I could be tempted by something with a bit more BW and possibly mixed signal capability. Shame many are out of stock. I'd be very interested to see how analogue video looks on yours, though it's hard to photograph the subtlety that you get with an analogue scope.

[AlanBeckett]

You've all got a bit ahead of me due to my current decrepit state
I'm getting there, honest.

Yes, there's no doubt that there are shortcomings with both High and Low Bandwidth Scopes. As with all Instrumentation it's best to think about what you're really measuring. I wish we still had SPCh, RIP.

Mark, it's a long time since I had dealings with tint low Bandwidth Signals, and even then I was never sure what I was looking at. I guess the Tek. Scope of choice would e the 5100 series, like this :-

   

I've got a couple which sadly don't get much use. Apparently there's a Plugin which is good for 10uV/Cm but I haven't got one - http://w140.com/tekwiki/wiki/5A22N  I bet that takes some driving.

Anyway, back to the matter in hand. 
I've tried to take Pictures of the beginning and end of the Trace, plus the Sweep and Gate Signals.

           

Sorry about the first Picture, but honest, it doesn't start cleanly. The odd thing is that as the Gate Signal doesn't go High until after the Sweep has started - it's much longer than the Retrace - I'd expect the Start to be 'Clean'.

I don't expect it's of any great consequence but I think I'll have a look at those High Value Resistors round the Gate Input. By the way, they're x10 Probes so they're quite hefty signals and I shortened the Leads to the Minimum I could manage.

Alan

[pwdrive]

How's about a TDR demo when everything's up and running.

Lawrence.

[ppppenguin]

Does the CRT really not have an internal graticule? You have to go back quite a long way to find Tek scopes using an external graticule.

I wonder if the probes are loading the signals. Easy way to check is to stick a 2nd probe on the same point and see if the waveform changes significantly.

[Mark Hennessy]

Apparently there's a Plugin which is good for 10uV/Cm but I haven't got one - http://w140.com/tekwiki/wiki/5A22N  I bet that takes some driving.

Wow - 10uV is getting silly! Though I'm not surprised that such a thing exists - after all, Tek wouldn't have been happy with Telequipment having the V3 plugin going to 50uV/div. And nice to have the variable BW too. The V3 has a 2.5kHz mode - not sure why 2.5 particularly, but I find it extremely useful.

Anyway, apologies for the thread drift

Looking at the schematic, it looks as if it ought to respond pretty quickly to the Gate signal - there's nothing to slug it especially. I guess it'll be easy enough to compare Gate input to CRT grid if you can think of an easy (and safe!) way to lose the DC offset. Have you got a x100 probe with a suitable voltage rating? I think mine might only be 1kV...

All said, however, if the Gate signal is coming from a decently-low source impedance, then it's hard to see where the problem might be.

I'm sure you'll get there

[ppppenguin]

"Wow - 10uV is getting silly! Though I'm not surprised that such a thing exists -...." I've got the similar 5A20N but that only goes down to 50uV/div. Rarely gets used but when it's needed it's excellent.

Here's a brutal HV scope probe with a brutal price tag too: http://uk.rs-online.com/web/p/oscillosco...s/6258570/

[AlanBeckett]

I doubt if it's quick enough for that Lawrence. I'd need a very long Circuit

That's a thought Jeffrey, I'll give it a try.

Alan