> To: amps@contesting.com
To: <amps@contesting.com>
> Date: Thu, 18 Sep 97 10:39:52 +0000
> Recently, I installed a Harbach RM-100 metering/diode board in my SB-220.
> It fixed a low HV meter reading and has performed admirably for a couple of
> months.
How long did the less than perfectly designed Heath parts work?
IMHO, many of these home remedy mods are a waste of money and time.
It's kind of like me selling you car wax along with a new tire
when you get a flat.
We'd change the bad tire, add the wax job, and could say "gosh,
the wax really helped fix the flat tire".
> This evening, I went to tune up on 80 meters and noticed below-normal
> output. While tuning, key-down, in high-voltage (SSB) position, I noticed
> declining RF output
> (measured on an outboard meter), coupled with climbing plate current over
> the key-down period, followed by smoke from the area of the metering board.
You might have a less than ideal RF bypassing now causing
heating in resistors Pete. This could be the red carpet welcome to
the world of aftermarket improvements, or it could be something
else.
I've seen some nearly perfect mods that added bypass caps than made a
resonant circuit with wire wound resistors self-inductance and caused
problems on some bands.
> Trying to figure out what was happening, I tried the amplifier key-down on
> 20 and 40 meter, and all meter readings seemed normal. I then went back to
> 80, and verified that the same combination of symptoms was still happening,
> both in HV and LV (CW) position. At this point, there was a popping sound,
> the plate current meter pinned (with the amplifier unkeyed), something went
> white-hot on the metering board, and I shut things off.
Maybe you have multiple problems centered around a sick tube or
tubes.
Gas problems or filament cathode shorts can come and go. The arc
itself will often breakdown gas and getter the tube. All the hardware
changes in the world won't fix your tubes if they are bad, despite
some claims.
73, Tom W8JI
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