To see if there are filament problems, I have found that attaching flea clips to the filament wires (not pins) and running leads outside the amp to a vtvm or vom is a way to see if there is a problem in the filament circuit. Since high voltage is involved, this is NOT something a novice should even attempt. It is ONLY for experts who are completely familiar with high voltage equipment and associated safety!
-----Original Message----- From: David <w...@cox.net> To: 'Jim Shorney' <jshor...@inebraska.com>; drakelist <drakelist@zerobeat.net> Sent: Tue, Jan 3, 2012 6:35 pm Subject: Re: [Drakelist] L4B oddity Agree. Using an ohm meter would show little unless zero. For example, if the resistance caused by the pin adds 0.1 ohm, then for a 15 amp filament, that is a 1.5 volt drop; 30% less than normal. If you had a grid to filament short you were right on time for the new year's fireworks. I have also read MANY YEARS AGO THAT THE REDISH COLOR IS A HEALTHY NORMAL, so unless there is a crack in the glass, running it hot when the filaments are fixed, should get it back to the right unclouded condition. Again, careful! Good luck. David Assaf, III W5XU -----Original Message----- From: drakelist-boun...@zerobeat.net [mailto:drakelist-boun...@zerobeat.net] On Behalf Of Jim Shorney Sent: Tuesday, January 03, 2012 10:26 PM To: drakelist@zerobeat.net Subject: Re: [Drakelist] L4B oddity Do you ever run with color on the plates? It's required that they get a little bit red in operation for the gettering to work. Also, just a tiny bit of extra resistance in the filament pin is all it takes to dim a tube. An ordinary Ohmmeter won't register the difference. 73 -Jim On Tue, 3 Jan 2012 22:00:06 -0600, richard radke wrote: >All, > >Thanks to everyone who made suggestions. Solder on the pins all look >ok. .5½'s on each filament. I'm guessing a grid to filament short/ >leak when it gets hot. I did notice a slight bit of clouding near the >top of the envelope that wasn't there before. Maybe from running the >filament with way less than 5V. Thoughts ? At any rate, a replacement >3-400Z is gonna be hard to find (out of production for >years) so I'll probably just get a new 3-500 to go with the one I >already have. > >Rick >W9WS > -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime." HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.1901 / Virus Database: 2109/4721 - Release Date: 01/03/12 _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
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