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Old 23rd July 2015, 08:51 PM   #1
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Join Date: Jul 2015
Default B&K 747 troubleshooting

Hi, I bought a B&K 747 tester on eBay that arrived today. It was advertised as fully functional.

So I went to test a 12AX7 and followed the Manual exactly. The tube tested normally and everything was fine.

But after that it just stopped working. The pilot light is on but I can't get a single tubes filament to even light at all

I've tried many different NOS tubes and multiple sockets and everything is not working.

Any idea what might be the problem?? I'm thinking I should just return it if it isn't an easy fix. Thanks!!
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Old 23rd July 2015, 10:06 PM   #2
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Join Date: Aug 2006
Location: Taxland, New Jersey
If tubes don't light, the first thing to check is an internal fuse in the filament circuit. You can see it in the attached schematic at the bottom of the filament winding.
Attached Files
File Type: pdf B&K Model 747 Dyna-Jet Tube Tester Schematic.pdf (157.5 KB, 15 views)
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Old 25th July 2015, 08:56 PM   #3
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Update: Checked the fuse, it has good continuity so I guess that's not the problem...

I did find one resistor that looked burnt and was cracking, so I replaced that but the problem persists. Any ideas on what might causing the issue? Thanks!!
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