re: parasitic construction.
-
Hi Bill,
-
I also had problems one of the first times I tried to
construct and install one of Rich's parasitic kits in
a floor console model Henry. The resistors got
really hot and failed.
The problem also surfaced on a very cranky SB
220, I was working through from years of neglect.
-
So I did the proper math home work to figure out
the coil inductance values for my suppressors which
were right in line with Rich's paperwork. My math
and testing came up with inductance values about
85 to 95% of the suppressor kit values.
-
Upon construction of my own model suppressors,
I noticed that very small changes in the physical
construction added or subtracted from the inductance
values. Indeed, it's very possible to construct two
almost exact physical size inductors that differ in
inductance value a dramatic amount. To much
inductance is really bad news in a suppressor made
with low wattage resistors.
-
To complete the amplifiers I constructed a batch
of coils with similar inductance values and ran them
through my test equipment (HP Network Analyzer
and a Sencor LC-102) to match up and tweak
the coils.
-
Rich's paper work mentions the resistors do/should
run warm/hot in operation. Using his values, parts
and information they do indeed run hot at the high
end of the HF bands. The tweak is the guy who
doesn't have lab test equipment to ensure the
suppressor inductance value is not a significant
amount over the desired value, else they have a
potential to fail in certain longer duty cycle conditions.
-
My fix was to actually "upgrade" the suppressor resistance
value to a higher watt rating and use close measured
and matched coils, being careful to er on the side of
slightly less than the desired inductance.
-
My results then and to this day have been dramatic,
not one of the many cranky amplifiers I've reworked
has shown parasitic probablems since my retrofits.
That includes my very cranky BTI 3-1000 amplifier
with a really squirly aged tube.
-
Rather than argue over any of this, I'll just throw out
that I prefer to use higher watt MF resistors than the kit
supplied values and I pay very careful attention to
the inductance values. In my examples, slightly less
L might not be enough (for the most part it often is),
and too much L is almost always bad for the resistors
when things are running full tilt.
-
Your results may vary.. my results are still on the air.
-
cheers
skipp wv6f
nospam4me@juno.com
http://sonic.ucdavis.edu I've added all three of the
vhf arcos amps and some tube data sheets.
-
-
[snip]
--------- Forwarded message ----------
From: "bill thomas" <k1xt@hotmail.com>
To: amps@contesting.com
To: <amps@contesting.com>
Date: Thu, 19 Jul 2001 13:44:41 -0500
Subject: [AMPS] Re: Parasitics
Message-ID: <LAW2-F1202HxYHLBQhE00000f77@hotmail.com>
I once had a Henry 2K-3 in which I installed Mr. Measures' suppressor
kit.
I thought I was doing a good thing. The first time I put it on 15 meters
several of the resistors exploded much as a shotgun shell would do. I
promptly went back to the Henry factory suppressors and never had another
problem, nor did I have a problem prior to that. For some stupid reason
I
was convinced that that bit of nichrome was going to save me from eminent
disaster. In my 25 years of hamming, never have I experienced a
parasitic
with my Henry 2K-3 (2x3-500z's), My AL1200 (3cx1200A7), or my Henry 3K
Classic X (8877).
This suppressor kit thing reminds me of the travelling salesman selling
cure
all elixir out of the back of his wagon. "Guaranteed to cure your gold
sputtered meatballs...."
Bill Thomas k1xt
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