Calibrating an OLD oscilloscope

[Nigel Goodwin]

Anyway, it doesn't have a working probe. And the connectors are not the usual ones for probes. Here is the manual. From what I can tell, the bottom two connectors are for ground and signal.

Any idea how I can get this thing working with a probe?

It's designed for use with leads having 4mm 'banana' plugs on the end, you can buy or make an adaptor to connect a normal BNC scope probe to it.

I made one years ago, I bolted a chassis mount BNC socket to a strip of aluminium and soldered a banana plug to the inner pin of the socket. I then plugged that in the input of the scope, and marked where the ground socket aligned with the aluminium. I then drilled a hole in the aluminium, and fitted another banana plug to the aluminium - result, a simple BNC adaptor that plugs in!.

Have a look at https://www.testpath.com/Product.aspx?pn=111-742 for examples you can buy - obviously you need to ensure the spacing is correct, but I have seen variable spacing ones!.

 

[Helloween]

Nice! Thanks very much for that, chances are that I can find something at an electronics store that will help me out.

I wonder if I've bought a bunch of junk, but the way I look at it, it's at least better than a cheap multimeter, and I got it for $20AUD, so I can't complain. With a $30 probe it should work out fine.

 

[Nigel Goodwin]

Nice! Thanks very much for that, chances are that I can find something at an electronics store that will help me out.

I wonder if I've bought a bunch of junk, but the way I look at it, it's at least better than a cheap multimeter, and I got it for $20AUD, so I can't complain. With a $30 probe it should work out fine.

For what you're using it for, in your car, the signal levels will be high, and source impedances low, so there's probably no need for an expensive scope probe? - just use a screened lead to two banana plugs.

$20AUD sounds fine, it's an old scope, but will be fine for most purposes.

 

[zevon8]

I haven't used that particular model, but I'm sure you will get alot of use out of it. Some of the older instruments have surprizing capabilities when used within their means. I had a very early 1960's EICO/Heathkit AC only scope that had one of the thinest, sharpest traces I have ever used. It was great for audio use, you could spot distortion a mile away on its CRT. Of course, all the ranges were continuosly variable, no calibration, etc etc, so everthing was a relative measurement, but for purely visualizing an AC waveform, it was superb. That scope seen action until about 3 years ago when it accidently fell over and did in the CRT.

-edit-
If you plan on keeping it, and I don't see why not, keep your eyes open for spare tubes when you are out at sales, auctions, etc. I kept a business card with tube numbers for my old test gear in my wallet, just in case I stumbled onto a find.

 

[Helloween]

Well, I've got it now, although I haven't tested it yet.

And geez, I certainly scored with this one. I bought it from a guy whose dad was a technician. And obviously a very meticulous one, because he kept the manual in good condition. He had since passed away and the son had no use for the scope.

And what's better, he had another scope that he put up for auction and didn't sell. He only wanted $50 for it.

It was a dual trace, 20 Mhz, solid state, bwd 530A. It had one probe, and a manual! As soon as I got home, I fired it up and hooked it up to the calibration signal. Yep... a nice square wave. I then connected it to a battery and tested the DC... that worked too. So satisfying to see that green dot fly past at varying speeds depending on the time/div setting!

So, in total, $70 AUD and I get a 10Mhz single trace and a 20Mhz dual trace scope. For that sort of price you would only get a multimeter if you got it new, and I notice that Dick Smith is selling a 20MHz CRO for $399, and a 10MHz CRO for $128.

One question... I will need to connect the little alligator clip on the scope to the car's ground, correct?

And another question... do you think these scopes will work ok for testing/debugging a small basic stamp circuit? My first aim is to build an instantaneous fuel economy measuring circuit that will take the injector and speed sensor information and compute l/100km. I intend to use the basic stamp 2.

Thanks for all the help!

BTW I edited this because it originally came out wrong, it made it sound like I took pleasure in someone else's passing, which certainly wasn't the case at all. Considering the seller had been jerked around by someone else previously who wanted it posted for $50, I'm happy it worked out well for both of us.

 

[Helloween]

If you plan on keeping it, and I don't see why not, keep your eyes open for spare tubes when you are out at sales, auctions, etc. I kept a business card with tube numbers for my old test gear in my wallet, just in case I stumbled onto a find.

That's not a bad idea... are tubes likely to go on something like this? From what I remember, a tube has a filament, so it will have a limited lifetime.

Cheers!

 

[Nigel Goodwin]

That's not a bad idea... are tubes likely to go on something like this? From what I remember, a tube has a filament, so it will have a limited lifetime.

It's very rare for the filament to fail, it's usually the emission of the tube that falls off - persoanlly I wouldn't worry about it!.

 

[zevon8]

The only reason I mention grabbing spares of the tubes is that sometimes they can be hard to find, or outrageous in price. It would be a drag to lose use of an instrument over one gassy tube. One tube I used to watch for was 12AX7A, or ECC83, one of my old generators had it, and due to a crappy design it could be hard on these tubes. I would see them at flea markets for pennies on the dollar in old radios. Depends on how much handling you gear gets also, how long the tubes will last.

 

[Nigel Goodwin]

The only reason I mention grabbing spares of the tubes is that sometimes they can be hard to find, or outrageous in price. It would be a drag to lose use of an instrument over one gassy tube. One tube I used to watch for was 12AX7A, or ECC83, one of my old generators had it, and due to a crappy design it could be hard on these tubes. I would see them at flea markets for pennies on the dollar in old radios. Depends on how much handling you gear gets also, how long the tubes will last.

Sorry - language confusion! - a 'tube' is the CRT (Cathode Ray Tube), ECC83's etc. are VALVES!.

 

[Helloween]

Sorry - language confusion! - a 'tube' is the CRT (Cathode Ray Tube), ECC83's etc. are VALVES!.

Well... are the valves likely to fail?

 

[Nigel Goodwin]

Well... are the valves likely to fail?

They do sometimes, but are reasonably cheap to replace - if and when you can find them.

 

[Helloween]

I made one years ago, I bolted a chassis mount BNC socket to a strip of aluminium and soldered a banana plug to the inner pin of the socket. I then plugged that in the input of the scope, and marked where the ground socket aligned with the aluminium. I then drilled a hole in the aluminium, and fitted another banana plug to the aluminium - result, a simple BNC adaptor that plugs in!.

Thanks Nigel,

I managed to solder up a BNC connector to two banana plugs to attach a scope to the s51B.

I fired it up, and after the tubes/valves began to function, I eventually began to see waveforms on the screen. I tested it against the same transformer I used with the other one the other day.

The trigger works really well on this one. I have not yet been able to get the trigger to function like it should on the other one, I'm not sure what I'm doing wrong.

Anyway, after all that I'm feeling rather pleased with myself and handy. Thanks very much for the advice on what to do, Nigel.