Digital oscilloscope

[Bushbaby]

As a matter of interest is the Tek T935a considered to be any good at all? I have a an HP39999A (built by HP trainees) waveform generator that I used it with over the weekend and it seems ok. It is my intention to work on my older valve equipment with an analogue 'scope so I want to make sure that I have one that I can rely on. If not, I will search for something better.
It is now my intention to sell off my Telequipment scopes (DM53, S54a and D61 as they all work but take up too much room).

Just as an outside matter of interest with regards to DSOs what is the opinion of the OWON SDS1102??

Best Regards

Rob

[Mark Hennessy]

Yes, I'm sure the T935a is a perfectly fine 'scope.

Personally, I'd take the Rigol or Siglent models discussed so far in preference to the Owon. It's got almost no sample memory, for a start...

[Bushbaby]

Hi all
I've just bought a Philips PM3305 at what I believe was a reasonable price. From what I have researched it appears to be a decent scope from the spec.

Any thoughts?

Best Regards

[Nick]

Hi all
I've just bought a Philips PM3305 at what I believe was a reasonable price. From what I have researched it appears to be a decent scope from the spec.

Any thoughts?

Best Regards

Not a bad scope but the digital section is very slow - only 4M samples/sec, so bandwidth in digital mode is severely limited. Looking at the spec, the a/d converters work at a maximum of 2M samples/sec - these are used to digitise the screen which is 8bit x 4000...meaning that the fastest scan that can be digitised is 2mS (4000 conversions at 2MS/s). As there are 10 divisions on the screen, that's 200uS/div which is pretty slow.

Note that it has a Rifa 220nF, 250V X cap (C101) that is prone to letting smoke escape. If not replaced already, might be an idea to do so... There are comments around that C101 is still live even if the scope is switched off at the front, so some folk have put a real on-off switch on the back, or just don't leave it plugged in with power.

Service manual attached.

[Bushbaby]

Thanks Nick
Thanks for the advice and I will check C101 when it arrives.
I have to say that I am very prone to OCD and check time and again that I don't leave anything plugged on my workshop bench.

Best Regards

[Murphyv310]

I have to say that I think you have made a mistake.
Personally I really think that you are running ahead, learn the basics then move on if you have a specific interest in where a DSO is most at home. For vintage work a decent analog cannot be beaten. Don't run before you can walk.
I've mentored many in my time including apprentices and many want to dive in and go way over their heads, a lot give up as they cannot grasp the basics as they run ahead and loose interest. Take your time to read, use YouTube, watch how others do things and learn.
Being a forum for vintage, recommending a DSO I personally thought was madness, way OTT for what you do. Remember using an analog scope you will know more about how to read waveforms their amplitude, time constants and frequency by simply observing controls and using a little mental arithmetic. At least you still have analog scopes and I recommend you spend time on learning how to operate them. I've been in the trade since 1970 and played with radios and TV for some time before that. I'd not even consider a DSO now, I've only ever used them in Sony when I did mobile phones and that wasn't the main part of my day to day job. Other than that I have never had the need for a DSO and if this is the part of electronics you want to stick with then I doubt you'll use it.

[ppppenguin]

The Tek 935 that you have is a perfectly decent scope for vintage work. It can do just about anything you're likely to need and do it well. Forget about the old valve scopes, they are for testgear enthusiasts.

As Trevor says, learn how to use your Tek 935 and it will be an extension to your hands and brain. A DSO is a distraction for what you are doing.

I need a DSO for some of my work. My Rigol 1054Z does a pretty good job at what for professional users is a dirt cheap price, c£300. I'm still happier with an analogue scope. The fact you've got a knob for each function; the very direct relationship between what you do and what happens on screen; the way you get to know its foibles inside out after a while. For those of us who do a lot of TV stuff it takes a very good (= expensive) DSO to display a video waveform with anything like the fidelity of analogue. My DSO isn't in that class. But when I'm looking at a few nanoseconds worth of waveform that happens only once in over 100ms, or one shot happenings in complex logic then I can't work without a DSO.

[Bushbaby]

Hi Trevor,
I did think that this was a real time analogue scope but had digital (albeit old) storage capacity too. It wasn't at a bad price either.

Best Regards

[Mark Hennessy]

Crikey Rob!

This is like having a barn full of classic cars, but you don't yet have a driving license! Your problem is not lacking transport - you haven't learnt to drive yet

Rather than throwing money at kit, you need to invest some time in learning about electronics. You can't buy that - you have to put the graft in.

But all that said, none of us know how you came by this new 'scope - perhaps the price was too good to refuse...

The good news for you is that this Philips 'scope is basically an early Combiscope. This means you can use it as an entirely analogue 'scope, and ignore the digital side of things. That is what I would recommend you did. Earlier I recommended the Philips PM3215 or PM3217. These are essentially analogue-only versions of the PM3305, but with improved specs. And they are simpler internally, so run cooler and are easier to fix.

Is it better than the Tek? That's a tricky one to answer. Personally, I like Philips more than Tek, but I'm fully aware that others will strongly disagree. I sometimes like to support the underdog - my radio collection has a lot of Hacker sets, but a fair few from Fidelity too

In this contest, they are quite closely matched in terms of spec, so it might come down to personal preference. The Philips PM3215 has a better control layout for beginners (which is why we bought loads of them for training), and this PM3305 is very similar (but with extra complexity for the digital stuff on the RHS) so you might find it a better instrument to learn on. But it takes more bench space because it's wider than the Tek.

As others have said, the digital modes are very limited by modern standards, and again, I would ignore them. But they're not as limited as some might think, as the low sample rate is mitigated by equivalent time sampling. This 'scope even has an LED to warn you when its switched from real time sampling to equivalent time sampling (the one labelled "Repetitive signals only"). Philips were always good like that.

I should say that quite a few posts have arrived since I started this, and I've edited it down quite a bit as a result. Part of the time taken to write this came about because I wanted to dig out an original Philips catalogue from 1987. If I had more time, I'd scan in the 3 pages detailing this model.

Just a word of warning - there is a later version of this 'scope in the newer plastic-chassis case that they switched to in the mid/late '80s (with soft keys and an LCD readout). We have one at work, but I can't remember the model number. While it still works well, I did notice that a PCB in there has loads of leaking surface-mount capacitors, and sooner or later, the electrolyte will start eating PCB tracks. I have no idea if the PM3305 uses similar caps - perhaps not, given that its older - but that's something I would check for ASAP. I haven't decided what to do with the one at work - there's no point having someone fix it given the cost of labour, but while it still works, it's hard to justify throwing it away. If we did, would I rescue it and restore it? Much as I love Philips, I really doubt it... I've spent many hours repairing a Tek audio analyser with that failure mechanism, and it's a constant game of whack-a-mole - you never know when it's going to go wrong again, and because the breaks are invariably underneath giant SMT ICs, you have to spend an age figuring out what needs to be linked to make it go again. Luckily they only used those caps on one PCB, but it's a massive one that had about 30 of them. Total nightmare! Don't mention 1990s camcorders

Hope this helps,

Mark

[BusyBee]

Especially after reading the comments here I would agree with Trevor on this. An analogue scope is, for the most part, far more useable. I have always regarded an oscilloscope as an instrument that needs time and not just a little experimentation and exploration to get to know. This is invaluable! I have the scope I now own by and large because the people I worked with did not understand it or see it's value in use so it was surplus to requirements as I was the only one who ever used it. The number of times over the years I have seen, particularly, students in colleges scratch their heads as they tried to understand, but scopes were somewhat on the sidelines of most courses. I suppose much of the modern push is digital but really one has to know what they are looking at and what to expect. I have never used a digital scope (although have at some point been perhaps confused by a logic analyser which I suppose is a specialised digital scope) but the way I see it an analogue process and display ought to be far more predictable.

Another side point which also occurred to me is that having and old scope (even valve, but I don't mean buy one) which is faulty gives opportunity to investigate scope principles without risk of damaging your daily service instrument. It's not something have had input to recently but do remember when at college I did get the opportunity to investigate a fairly simple fault on a college oscilloscope. It did improve my knowledge and confidence of looking into non everyday things. I remember that fault was something which could likely occur on a modern analogue scope even though the one I was working on was valve.

Tracy