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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Apr 2017, 9:28 am   #1
M0FYA Andy
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Default CRT Tester

Has a circuit ever been published of a test-set for testing WW2-era CRTs such as the VCR97 and VCR517?

I have a bunch of these tubes of unknown status and would like to test them. As the VCR97 was popular for home-built TVs in the 1950s, it may well be that a design was published?

I would be surprised if there wasn't a tester available 'back in the day' to test these tubes in service in Gee or radar equipment, but I've never seen reference to one. If one did exist it would be nice to replicate it!

Any ideas, folks?

Many thanks,

Andy
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Old 14th Apr 2017, 9:44 am   #2
llama
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Default Re: CRT Tester

I think you'd be hard-pushed to find a tester that is any simpler than the PSU and timebase section of one of the many TV circuits from back then. I have in mind the Simplex, Argus and maybe one of those from Inexpensive Television booklet. As well as testing emission for you they would also demonstrate any shading present - I believe many VCR97s had deflection plates closer-in than is ideal for TV use but probably perfectly OK for a 'scope.

My only reservation is that most of these used mains EHT which is especially dangerous in a testing/mockup scenario. For EHT I'd find one of those little 5 inch TVs and use that. (I once got one at a car boot sale for 20p!).
Graham
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Old 14th Apr 2017, 9:46 am   #3
Heatercathodeshort
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Default Re: CRT Tester

Hello Andy,
These tubes are very difficult to test on a simple emission tester set up.
I recently checked about a dozen tubes in an 'Argus' and found all but one very low emission giving a very dim picture. You will also discover that many do not produce a full scan due to incorrect positioning of the deflector plates. This did not matter with their original use as Radar displays.
The poor picture examples gave a reasonable reading with a conventional CRT tester. I think the main problem was due to the huge gun assembly releasing molecules of gas after evacuation. These tubes were manufactured in great haste and were unfortunately not expected to enjoy an extended life due to enemy action.
They were produced by many manufacturers, no doubt some better than others. I think you may have had a better chance with examples manufactured by the GEC [UK] as they had a wide experience of manufacturing electrostatic tubes. Regards, John.
Sorry Graham, Snap!
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Old 14th Apr 2017, 10:13 am   #4
M0FYA Andy
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Default Re: CRT Tester

Thanks for the replies.

My application for these tubes would be the original one, so for use in restored/rebuilt Gee or H2S indicators.
Rather than struggle with an untested tube in an untested unit, it would make sense to prove the tube first in a dedicated test-set.

Mains derived EHT should be OK as I would want to build something properly, not a lash-up with exposed high voltages. I think we'd be talking up to 2kV, not something I'd want to touch!

If need be I could design something, based on other circuits, but I don't want to reinvent the wheel unless I have to!

Andy
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Old 14th Apr 2017, 10:24 am   #5
line sync
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Default Re: CRT Tester

That is a very good question andy.
All I can add is that I`ve read all the Practical television magazines from the 1950`s & 1960`s and I think if a tester circuit was published I would have remembered it.

Robin
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