Thoughts on old valve-based oscilloscope

[Agent24]

I was in a second hand shop type place near my house recently and noticed they had some quite old equipment for sale.

Of most interesting (to me anyway) was an oscilloscope, a "Hartley Electromotives CT436"
http://www.thevalvepage.com/testeq/h...t436/ct436.htm

The price tag is $69 (NZ) but I would assume I could get it for less - that is, if there is any point.


Assuming it was working (or could be fixed) would it be of any use? I don't currently have an oscilloscope but I'm guessing I'd probably want one made this millennium?

What do you guys think?

[Toasty]

Re: Thoughts on old valve-based oscilloscope

Not unless you starting a museum or adding to one's collection....?

>>I'm guessing I'd probably want one made this millennium?<<

More likely in this decade.

Clear Lucite side panels and a low rpm motor and you've got a centerpiece for your table.

[Agent24]

Re: Thoughts on old valve-based oscilloscope

More likely in this decade.

Figures, but I'm guessing anything decent from the last 10 years will be a lot more expensive than something that was decent and even older.
(Though maybe not 1966 Valve-based old!)

All the cheap ones made recently look to me like made-in-China pieces of junk.

And, I do want something good, but I can't pay a heck of a lot. I figure something old but of decent brand should not only be a good price but also good quality.


I think I need more research and knowledge before I really know what kind of scope I actually should get, though.

[Krankshaft]

Re: Thoughts on old valve-based oscilloscope

A whole 5 mhz ? Tube equipment is more trouble than it's worth especially since most of the paper based caps met their maker decades ago.

The best bang for the buck are late 70s early to mid 80s Tektronix scopes. HP/Agilent is another good brand but they are usually even more expensive used than Tek.

A scope isn't something you should just buy for the heck of it you should need to use it for something. Decent used scopes aren't cheap. Well much cheaper then the grands they cost back in the 80s .

You're probably better off looking locally most people who sell locally have no idea what a scope is worth and you may get a good deal.

[Agent24]

Re: Thoughts on old valve-based oscilloscope

First thing that comes to mind would be checking ripple on SMPS, I would really like to be able to do that.

Then there's just general stuff like "check for 450khz wave on pin 3" ...

[Krankshaft]

Re: Thoughts on old valve-based oscilloscope

The frequency of the ripple on the output of a switcher is in the Khz range but if you buy a scope buy a bit more than you need.

A 100 mhz Tek 465 can be had off e-bay for very close to 200 if you are patient and wait for one. The 475 the 200 Mhz model I was able to snag calibrated for 255 a bit more bandwidth for not much more cash. I had to wait around a month though. My budget was 300 bucks so I wanted the highest bandwidth at that price.

Is it overkill for switcher ripple measurements absolutely but make a wise purchasing decision once and you won't have to buy a scope twice because in the future you decide to measure something out of it's frequency range.

Comparatively a nice entry level digital the Rigol DS1052E at 50 Mhz is around $375 new but you can hack the firmware and make it a 100 Mhz scope. The reason being is that the 50 Mhz model is the same internally as the more expensive 100 Mhz model and the only thing stopping it is some code in the firmware.

[stj]

Re: Thoughts on old valve-based oscilloscope

if you did buy an ancient scope you'd have to re-cap it, and recalibrate it.
and the rotary wafer switches can be a real pain to clean.

one last thing, valves contain heaters - heaters draw a lot of current.
the transformers weigh a fucking ton!

[Agent24]

Re: Thoughts on old valve-based oscilloscope

I doubt it would move far from the bench so weight wouldn't be much of an issue.

Still, I guess it would make more sense to get something with only one tube in it

Thought it could be fun to restore it but I'd probably run out of money before I got there...

[Th3_uN1Qu3]

Re: Thoughts on old valve-based oscilloscope

I have a C1-71 russian oscilloscope, i picked it up for $120 locally. It has about 200MHz bandwidth, and its internal calibrator can also output DC besides the 2kHz signal so i can calibrate my cheap multimeters against it.

I got full schematics along with it. I asked the seller about the Chinese scopes and he said "Well this one, you'll find parts for it today, next year, or 10 years from now. The chinese ones, it's not that you can't find replacement parts, it's that you have no idea what some of them do."

It does seem to have a couple valves besides the CRT but IIRC it's just voltage regulation stuff. It is heavy though - at 15kg it isn't the type of tool that you can move around easily. But it's proven very useful for my understanding of SMPS supplies. I even checked the FSB on a Pentium III with it - at 100MHz it doesn't appear exactly square, but it's enough to determine that it's there. Its only downside is that it absolutely requires to be earthed to work stable, so it cannot be used to probe the primary side of switchers without an isolation transformer between SMPS and mains.

Since i have an interest in radio circuits as well, the high bandwidth helps a lot. Also, i've seen ringing in SMPSes as high as 64MHz. You *need* this kind of bandwidth to be able to notice such things, and they can be the difference between a supply working within spec and fried silicon.

[stj]

Re: Thoughts on old valve-based oscilloscope

have you got 200+ mhz probes then?

[Th3_uN1Qu3]

Re: Thoughts on old valve-based oscilloscope

Well, it didn't come with probes so i built them myself. All i know is that the x10 probe i built will display a 33MHz square wave just fine, so i think it's good enough.