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  #1  
Old 06-01-2011, 09:41 AM
JCFitz JCFitz is offline
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Glass test tubes suitable for a Zenith Porthole?

Since my blonde Porthole combo issue showed alignment issues when it was powered (sound not tracking with the picture especially) and the traps are all dangerously close to that metal tube I was wondering what tubes will work as test tubes in this chassis?

It's the 24H20 chasis with 16AP4


I found a couple of crts currently on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

Will either work?
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Old 06-01-2011, 10:00 AM
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John Marinello John Marinello is offline
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Your chassis uses a 16GP4. On the 10BP4, you would have to move the focus
coil rearward 1 3/8" to get a sharp picture, but then you'll lose much of the image due to the deflection angle differences. Or, you can insert the tube in the yoke that much less, and get a sharp circular image due to neck shadow.
Rather a cumbersome tube for test purposes. No on the 8YP4. You would need either a 5AXP4, or a 8XP4. Or, you can just slip something between the 16G and your hand so you don't get nailed.
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Old 06-01-2011, 02:00 PM
TV Engineer TV Engineer is offline
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You shouldn't align the IFs with the horizontal sweep circuits operating, as the harmonics of the sweep frequency will interfere with your scope trace. Also, killing the sweep will also kill the AGC, which you need to do to fixed bias the IFs before aligning.

So, the metal CRT shouldn't even be a consideration.
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Old 06-01-2011, 07:11 PM
JCFitz JCFitz is offline
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Thanks guys. So I need to disable the sweep anyway.

I figure the deflection angle was all wrong on the Sylvania tube. Was curious about the 10".That's all. Just thinking about having test tubes as I get into older sets and what will work for certain tubes.
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