EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Anthony Brady on March 22, 2016, 11:06:40 pm
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I was wondering if there are any testers for checking an oscilloscope CRT the way regular tubes are checked? There are CRT testers/rejuvenators out there from the old CRT TV days such as the Sencore CR70, CR143 and CR7000 testers. B&K has their 465, 466, 467, 490A and 490B CRT testers. But, are any of them capable of testing/rejuvenating a Tek 465 oscilloscope CRT?
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There are a couple of Yahoo Tektronix groups you might consider. There are
experienced senior Tek engineers, many retired, that support those sites.
Regards, Dana.
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Testing and rejuvenating are two very different things. You can always test a tube by putting it in a functional 465.
My very limited understanding is that rejuvenation sometimes works, but only for a short time.
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Anthony,
I used a Sencore CR70 to rejuvenate the CRT on a Tektronix 2755AP spectrum analyzer with a low brightness. It did a good job recovering the dim tube. Don't recall all the settings but I do know it boosted the cathode voltage and Grid briefly. I think I tried checking the grid current but did not get any usable results so I just proceeded with the rejuvenation. Most CRT's used in test equipment are not well documented on the Sencore and BK CRT testers. Most importantly you want to find out what the CRT's cathode voltage runs at on the system as a basis for the setting. You will need to use what is called a universal adapter - basically hook clips on the pins of the CRT. The 2 labeled "F" are filaments and the "G1" is typically the Grid. You can hook the rest up but these three are the key connectors.
I did come across a write up with some information that may be of some interest.
http://www.thegleam.com/ke5fx/crt.html (http://www.thegleam.com/ke5fx/crt.html)
Fortunately in your case there are there were plenty of 465's manufactured for potential spares - It's harder to source Tek's SA CRT's.
-rastro
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My Sencore cr70 has a separate switch setting for 'scope tubes. I have a 465 no suffix scope with either a circuit issue or crt is not wicked bright. Its been usable, but I always wanted to go through it eventually.
I'll have to look into at least trying to test the CRT. I'm not sure if 'scope tubes are listed in my setup book, what is the CRT number?
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My Sencore cr70 has a separate switch setting for 'scope tubes. I have a 465 no suffix scope with either a circuit issue or crt is not wicked bright. Its been usable, but I always wanted to go through it eventually.
I'll have to look into at least trying to test the CRT. I'm not sure if 'scope tubes are listed in my setup book, what is the CRT number?
Before potentially damaging your CRT, I suggest you see if there are any problems in the HV or DC restorer circuits - the diodes and capacitors are a frequent failure point.
N.B. a month ago I have never been near a CRT, but I had brightness problems with a 465. In my case the tube was internally terminally faulty; the grid was disconnected.
I strongly suggest you have a look at the Yahoo! TekScopes group. Their archive is searchable, and the denizens were very helpful and welcoming to me.
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If you do need a new CRT then don't just look for 465 ones, possibly any side plate 10x8 CRT will work. The 2445 series are probably too short unless you get the screen, but there are lots of TV video CRTs now available but most aren't side plate.
Even HP, Philips etc CRTs will possibly work.
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I agree with tggzzz eliminate all possible problem sources before touching the CRT.
Rejuvenation should be at the bottom of the list since there is always the possibility of damaging or shortening the life of the CRT.
-rastro
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If you do need a new CRT then don't just look for 465 ones, possibly any side plate 10x8 CRT will work. The 2445 series are probably too short unless you get the screen, but there are lots of TV video CRTs now available but most aren't side plate.
Even HP, Philips etc CRTs will possibly work.
http://www.reprise.com/host/tektronix/reference/crt.asp (http://www.reprise.com/host/tektronix/reference/crt.asp) contains CRT to Instrument Cross Reference Database, plus other useful information.
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In my case the 465 tube was terminally damaged: the grid was internally disconnected. Rather than throw it out, I decided to chop it up and put the pretty bits in my display cabinet.
The results, including pictures of the hidden metal mesh lens, can be seen at https://entertaininghacks.wordpress.com/2016/03/09/rescuing-a-broken-tektronix-465-crt/
Those interested in the Burr Brown equivalent of the Pirelli calendar can look at pretty scans of thick-film hybrids at https://entertaininghacks.wordpress.com/2015/07/07/images-of-late-70s-burr-brown-thick-film-hybrid-ics/ (Yes, other people have described them as "geek porn" :) )