Gifts from Mom: Tube Tester & a Scope!
 

I've never once seen a tube tester at the local flea market, but leave it to my mom to actually be the one to find me what I'm looking for! She said "I bought you something you've been needing"... and boy did she ever! She got me a tube tester AND an oscilloscope for $5 a piece! I couldn't believe it!

http://img705.imageshack.us/img705/7778/img0591mv.jpg

The seller was an older fellow who told her that they still worked to his knowledge but hadn't been used in a long time. Still, the price was reason enough for me to fear the worst. However, after a careful inspection and cleaning, I was delighted to find that they actually appear to be in perfect working order!

The tube tester is an Accurate Instruments Co. Model 257:

http://img823.imageshack.us/img823/192/img0593x.jpg

It's a basic emissions tester that seems to handle a great variety of tubes for radios and televisions, including cathode ray tubes. I was pretty happy about that, since I probably won't be going out on a limb to buy a dedicated CRT tester and this may be just good enough in the event I ever run across another potential tv project. I downloaded the tube charts for this tester on the internet and printed out all 67 pages of it. So far, I've been able to test every type of tube used in my Zenith television and most others out of my radios. Nothing weak out of my television so far, but my Admiral console radio has a couple that are weak...

The oscilloscope is a Lectrotech Model TO-55:

http://img295.imageshack.us/img295/8643/img0592k.jpg

It wasn't really all that dusty inside, and I'm still cleaning the case which has some paint overspray on it in spots. It seems to run fine, although I don't know so much about oscilloscopes. I was able to adjust the rate at which the the beam swept across the screen, adjusting it's horizontal and vertical orientation, brightness, and focus. I'm not sure what kind of leads I need to hook up to this to take measurements. It has this one attachment, though...

http://img811.imageshack.us/img811/3922/img0594r.jpg

Unlike the tester, I haven't really found too much online about this scope. Hopefully, I'll find a instruction manual or maybe someone will point me in the right direction. Can't be too hard to figure out, I suppose. I just simply haven't used one before. I imagine it would be helpful in troubleshooting my Zenith.

Congrats! Those are really nice gifts. I never get anything like that :no:

Great stuff. My wife would never bring more electronics home, even if she knew what it was :)

Obviously you have a most wonderful Mom!!

It looks like you have the probe for the scope, which is a good thing since it's older. You can try measuring the voltage of a battery (like a "AA") with the scope, using the point for pos, and clip for neg (though it doesn't matter, if you reverse it, it will move down). Do this before messing with high voltage. And if you don't know or understand the risks, don't do anything.

With the battery, you'll see the line shift up or down 1.5 V. If you set the divisions for 1V, it will probably be about right.

You can go to the tektronix website and view or download some of their primer's on oscilloscope use. While the scope is different, the principle is the same.

Nice Gift!

JW

I think zenithfan1 has the Lectrotech TO-50. Does yours have a vectorscope mode?

John

you do have a wnderfull mother. i wish i still had mine she left this old world at 61 years young. treasure her she is the only one you will ever have. great gifts by the way.

Thanks guys! I wrote Zenithfan1 in regards to his Lectrotech. According to his old post, an electrolytic failed in it. Hopefully mine will be alright, but I guess if I ever find any problems, I may need to do a recap as well.

I'll be reading up on how to use these a bit more, but today I just experimented a bit. I was able to get a neat effect by connecting it to the speaker of my guitar amplifier. It's interesting to see what the sound "looks" like. At least I know it works.

I can get something of a wave to appear just by touching the probe with my finger:

http://img440.imageshack.us/img440/9100/img0599jx.jpg

This is with the volt/div set to .02 and the time base set to 1.

Cool. Looks like there's a 1V squarewave calibration source right above the GND. Try touching your probe to it. If all is well, you should see a nice squarewave.

Like this?

http://img714.imageshack.us/img714/5408/img0602pd.jpg

My probe is marked "PR-10" and has a switch that goes from "DIR" to "LO-C" Any idea what that stands for? I made this reading using the DIR mode. The LO-C setting shortens the height/voltage by at least 75%.

DIR=Direct, Lo-C = Low capacity, used for AC measurements. Doesn't load circuits as much as direct.

Get yourself a copy of Tektronix's "XYZ's of Oscilloscopes" (FREE) or one of the Howard Sams Publishing books on using O'scopes - I think Bob Middleton was the author. Great finds, BTW.

Cheers,

Thanks, actually I found the Tektronix's primer for oscilloscopes last night and I'm still reading it. Lot's of interesting information and I'll be sure to soak in what I can.

One problem I had with the scope isn't a electronic problem, but rather simple but annoying matter with the faceplate that goes over the CRT. It's not the plate, but rather the little plastic nuts that hold it in place. They're easy to get cross-threaded and one got stuck a certain way that when I took it back off, it actually loosened the threaded shaft and loosened the nut from the inside! I had to pull the tube out to reach that tight corner and I've made a point to be careful with these plastic nuts.

Anyways, while I was in there, I noticed that the CRT doesn't use a magnetic deflection yoke like that found in televisions. Rather, the tube itself has many more pins on it's base than the average CRT and I take it that these actually send the horizontal and vertical sweep signals. I'm not sure how it works, but I suppose there's something built into the tube that creates the deflection without the help of an external magnetic source.

What I wonder, is how does this work and why is it that this method wasn't used in televisions?

It uses electrostatic deflection which has a much higher bandwidth than magnetic deflection. Some early TVs did use it like all those little 7" sets with their 7JP4 CRTs. I'm not really sure why magnetic deflection won out. I suspect it was lower cost or perhaps electrostatic didn't work well with larger screen sizes.

Ah, I see. I hadn't read much about electrostatic deflection until now. I guess the electromagnetic method was just better suited to televisions. Perhaps it was easier on the development process as CRT's got larger.

I've been looking into this whole oscilloscope thing in more detail and I think I've about got it figured out. Looks like it's not too hard to dial in waveforms, once you have an understanding of how they'll appear and what you need to adjust to bring them into view. Took some readings today on my Zenith, starting with the 12BY7 video amp. With those contrast problems I've had, I'll probably be poking around in that area a good bit. I just tweaked the controls until I got something that matched the waveform on the schematic.

Here's what pin 7 off the 12BY7 looked like:

http://img151.imageshack.us/img151/8591/img0606o.jpg

And pin 2:

http://img175.imageshack.us/img175/1161/img0607v.jpg

Really interesting stuff! It's cool to see how the waveform fluctuates, corresponding to the moving images on the tv screen. Not making any specific measurements here, just trying to get a good waveform that matches the schematic. Good sign that I'm starting to "get it" and will hopefully be able put this instrument to good use.

One hint of advice on that tube tester. For an accurate test drop the filament voltage down one notch. IE, if it says E drop it to D.
Doing this will give you a good idea of the tubes actual condition and life left.