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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Origin of Hickok Roll Chart Data Remains a Mystery posted by Chris Haedt on September 3, 2003 at 13:39:30:
You wrote "Wendell wondered how a TV7 COULD be reset to line with plate current flowing--and so do I--unless a separate AC voltmeter was used to monitor the primary of the power transformer."It's easy: On a TV7-B/U pressing S3 (mut cond) puts the tube into test mode with plate current. While keeping S3 depressed just push S1 (line adj), It appears to transfer meter over to line measurement circuit w/o upsetting anything in the mut cond circuit. By independent measurement, all element voltages and currents on tube remain unchanged when the line adj button is depressed simultaneous with mut cond. button. I've observed same arrangement on a number of tube testers inc 752/A, 53?, 800 and on Weston 981A. What I find interesting about this is if it was (is) such a "forbidden" mode of operation why didn't they add the mechanical interlock to prevent it? The more I dig into these things the more mysterious they become.
Although the case is definitely building for not adjusting the line voltage during test, the evidence is circumstantial and indirect. There's lots of dos and don'ts in the manuals but nothing about not adusting the line voltage during test. Again, you'd think that if it was important it would have warranted a specific mention like so many other non recommended set-ups.
I think I've figured out how Hickok accounted for the filament sag in some cases: They state that the test button should be depressed only long enough to note the reading: any longer may damage the tube. Don't know about the damage but if under test conditions for only a second or two, indirectly heated cathodes probably won't cool off much. Wonder what happens with directly heated cathodes?
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Follow Ups
- Re: Origin of Hickok Roll Chart Data Remains a Mystery - Steve O 20:24:33 09/03/03 (2)
- Re: Origin of Hickok Roll Chart Data Remains a Mystery - Chris Haedt 04:27:50 09/04/03 (0)
- Re: Origin of Hickok Roll Chart Data Remains a Mystery - dave slagle 21:04:12 09/03/03 (0)
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