Old fuses can fail due to fatigue over the years. They develop a sag after repeatedly being thermally challenged by a current surge such as filament in-rush.
Dennis AE6C On Wed, Apr 28, 2010 at 2:24 AM, Ron <[email protected]> wrote: > Curt, > FWIW, I had a TR3 that did the same thing years ago. Put in a new fuse and > it continues for years. > 73 > Ron WD8SBB > > --- On Tue, 4/27/10, Curt <[email protected]> wrote: > > > From: Curt <[email protected]> > > Subject: [Drakelist] T-4X filament fuse brunout and other strange > behavior > > To: [email protected] > > Date: Tuesday, April 27, 2010, 10:16 PM > > I had a surprising experience today > > when turned it, lights briefly came on then turned > > off. Turned out the filament fuse ( evidently the > > original ) had blown. Thinking maybe a tube filament > > had shorted, I checked current draw, 5 amps peak at turn on > > dropping to about 2 after warm-up. The fuse is an 8 > > amp fuse, and seem to recall fuses aren't quick to blow > > unless current is about 150% of the rating. > > > > So, does this just sound like a tired old fuse finally > > giving up, or is there something else to look into? > > > > Also, the plate current behavior seems more sensitive to > > drive than it used to be. On 40M, about 1/4 turn to go > > to 150 ma, then a very small amount more drive rotation > > causes the plate current to jump up to 250 ma. Efficiency > > doesn't seem as good as it once was either. 150ma used > > to show 40W on the tuner output meter, now about 25W. > > Bias cuurent set to 70 ma. PA tubes dying? Driver > > dying? both? > > > > 73, Curt KB5JO > > > > _______________________________________________ > > Drakelist mailing list > > [email protected] > > http://mailman.zerobeat.net/mailman/listinfo/drakelist > > > > > > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist >
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