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Yes, getting parts is a problem for anything this old, be it electronic instruments, cars, or old clocks. In order to operate this business, especially with the warranty on our oscilloscopes, it is absolutely vital that we position ourselves to supply parts for repair.
Fortunately, Tektronix left behind quite a legacy of parts when they moved on into newer forms of instruments. Many of these were in private hands, such as laboratories, government agencies, and big electronics companies like Motorola. Other parts were in the hands of the Factory, and along with the others, gradually found their way into the hands of companies specializing in obsolete parts supply.
As more of these instruments fall into the hands of collectors, and other friends of the make, there is a need for more restoration parts. The sheet metal on an instrument probably doesn't affect how well it works, but it does affect how it looks. And collectors want the unit to look like new.
Many Tektronix parts were generic, but many more were especially made for, or by, the Factory. Often the only way to get these parts known as "unobtanium" is by taking apart a "parts donor." Here at The Oscilloscope Store we have access to all these kinds of parts: New, NOS, used, and donated. Fortunately, these instruments are rugged and easy to fix.
A WORD ABOUT CRT'S
The crt is the heart of an oscilloscope. If it is not working right, then the unit is probably not going to be of much use. Replacing a crt is a serious job, but getting one can be at least as serious.
WHAT GOES WRONG WITH CRT'S?
A crt has a filament just like any radio vacuum tube. Most of them can be checked by using your ohmmeter between pins 1 and 14 on the socket. Dual gun crt's (502, 555, 556) have two filaments. Check the other one between pins 3 and 13 (555) or 4 and 12 (556).
The phosphor on the face of the crt is easily burnt by setting the intensity too high, or leaving a spot motionless on the screen for too long. You can see these burns as brown or black spots in the white coating. They may be far enough out of the viewing area to not be a bother.
A crt has a high vacuum. If air leaks into the crt, it won't work very well. Sometimes you can tell if there is air in the tube by looking at the getter. That is the bright aluminum spot on the side of the glass where the getter was burned to get those last few molecules of air. If it is bright and shiny, the tube is probably ok. If is is milky or cloudy, it has probably been exposed to air.
Finally, you can gently shake the tube and listen for loose things inside. Some rattling is normal, but if chunks of stuff are floating around in there, it is not a good sign. On these older tubes, the base often comes loose. Even on new tubes this can happen due to aging of the glue. These need to be dried out and the base reglued. All of my tubes have had this done.
WHAT IS THE PROBLEM GETTING A REPLACEMENT CRT?
The biggest problem is that thousands of these tubes were destroyed when companies, universities, and other agencies stopped using these instruments. Thousands more are stored away, not available for purchase. So it may take a while to find one that is meant for your model. Even when you do, it may not work.
Shipping a crt in anything other than its factory box can result in breakage.
You may see an ad for one "New in box." Just because a crt is in a factory box doesn't mean it is new. Or that it even works. Techs often put the old tube back in the box for a spare, or for disposal. So be wary of these ads. If the box is still stapled shut with TIGHT factory staples, the tube probably is new. If the original packing, parts, and instructions are in the box, that is a good sign. As are the neck pin protectors put on all new tubes at the factory.
SO WHAT'S DIFFERENT ABOUT MY TUBES?
The one major difference is that I have a model of every scope that I sell a tube for. Every tube I sell has been put in a scope and tested. If it is used, new, new-in-box or factory sealed in box, I still test it in a scope. I rate the tube from its operation, not from the box. I also clean it and repair the base. Then it is repacked for shipping. When you buy a tube from me, I check it and if there is any problem with it, your money is immediately refunded.
A very useful Tektronix crt cross-reference website can be found at:
http://www.reprise.com/host/tektronix/reference/crt.asp
If you have any questions or would like additional pictures please email me at tekstore@telus.net
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