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  #1  
Old 01-02-2014, 10:13 PM
egrand egrand is offline
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Help with Sencore CR31a CRT Tester

Does anybody else have one of these? I picked one up over the summer and it seems to work on all the functions except setting the filament voltage. When I set it for a particular volt range it shows on the meter somewhere in that range, but when I try to adjust the variable knob it only changes it about .1 volt on either side. For instance, when I set it to 6.3 volts the meter shows 6.6 and I can only adjust it between 6.5 and 6.7. When I checked the actual voltage at the socket it is 7.5v and still only adjusts .1v. Similar results on all the other ranges.

I'm thinking testing a CRT at that much higher voltage will throw off the other tests. I also think it should have a wider range of adjustment. I've replaced all the electrolytics and tested the resistors. The only resistor I replaced was the 15K 1W that was reading 16.6.

Could the transformer be bad or the diodes? I'd sure like to use this as it has 21 different adapters and a HV probe. I got a B&K 470 at the same time, but it doesn't have all the adapters for B&W. I bit the bullet and ordered the stuff to make my own universal adapter for the B&K, but I'd still like to get the Sencore going since I've got it.
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  #2  
Old 01-03-2014, 05:53 AM
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earlyfilm earlyfilm is offline
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OK, lets think this problem through, back up and test.


Take ten watt 10 Ohm resistor and connect it to the filament leads of the tester.

(This closely simulates the filament load of a typical vintage B&W tube, say a 10BP4.)

Turn your filament rheostat all the way down and turn the tester on.

See what the meter on the tester reads and at the same time read the voltage across the resistor with a normal meter and see if both meters have the same voltage adjustment range.

This test should give you enough info to determine where to start look for the problem.


James.
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  #3  
Old 01-03-2014, 07:28 PM
egrand egrand is offline
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Ok, I got it. I guess it has to be under load. I used a 12ohm 5w and can get between 5.5v and 7.2v. I had to re-calibrate the meter. I'll try it out in a little bit.

Thanks!
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