I had posted before at my progress in bringing my fl2100b back to life.
A chance here to laugh at the "microwave generation" (me) :)
I rewound the burnt plate choke. Used 27awg 200C magnet wire.
covered it with some red hi dielectric varnish, although I suppose some
might say
that's ugly. Interesting how the plate choke positioning between the tubs
makes it get warm, independent of any rf heating. I split/sized the windings
the same as the original yaesu choke. It dipped okay, with no resonances
around
operating freqs. I was thinking of using a different choke, but the 3/4"
yaesu
coil form was needed to fit well. (larger diameter not good physically)
In putting everything back together, I found what caused the black smoke
trace
in the tank area. One of the 200pf doorknobs in the input tanks had
separated
one of it's terminals...it had looked damaged, but it didn't come apart
fully
until I pushed against it. (I guess "blown apart" would be more accurate)
I replaced that with a HEC HT50 200pF. That cap seems sufficient in this
use.
(I'm sure to get a comment on that?!).
I think the various bits of damage I had were incremental. I don't think
everything
went at once. Hard to say what came first. Remember there were some wrong
components, bad previous repairs.
Soldered everything back up that I had taken out...eyeballed it against
the schematic a couple times. Made some measurements with the tubes out.
Plate voltage looks good. Grid looks good.
Put the tubes in...Got some glow...Tried keying it...Nothing. No change
in plate current. The plate current reading was low and just wouldn't move.
Hmm. Measured a bunch of stuff. Bias voltage was -20v off, -2.3v keyed.
Played with adjusting the bias voltage lower. Nope. no change in idle
plate current.
That's odd I thought. But the tubes couldnt' have died, I thought. And
they seem
to be glowing right.
Kind of interesting trying to think it thru when one knows one doesn't
know that much,
and almost anything can be wrong because you undid/redid a bunch of it.
So I'm looking at the tubes, and notice the little side pin coming out
of the base.
and how the clamp around the base is tight up against it. Odd, I think,
maybe they
do that to tension the clamp. But oh, around the other side of the clamp
there's
an indent...ah! I had checked the tube pins before inserting..They are
different sizes,
so I had just eyeballed the socket and the pins, and when it went in,
figured, yeah
I keyed it right...
Evidently not.. tube pins can go in pretty much any way, into these
sockets at least.
So I was off by 90 deg. Thinking about the voltages on the various tub
pins there (572b),
I don't think I killed anything. (comments?)
Rotated the tubes, and things are looking much better. idle plate
current acting normally.
Tubes glowing more normally.
Laughed at myself. Kind of the newbie level of error you guys never even
give
a moment's thought to...:)
-kevin
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