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
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