Hi, Hank.
Well, I have various very high power resistors, so by using them in
various combinations with some large variable capacitors I can generate
various VSWR loads. I can measure the actual R +/- jX for each combination.
I recently built a very high power and wide range antenna tuner using
components (large variable caps, large rotary inductor, and large WWII
surplus switches that can switch in some very high power Russian ceramic
doorknob capacitors) that I have collected over the years. I think I
could use it to drive the VSWR loads without burning up my amp.
I also have a spare common mode choke built to K9YC specs, and Lowes
sells an infrared temperature "gun" in their electrical department (only
about $40, if I remember correctly).
I'll also have to build a simple RF current meter to monitor current at
the choke.
The only problem is that something popped in my big tube amp (QRO
Technologies HF-2500DX that uses two GU-74B tubes). I think one of the
tubes shorted and I've already burned in the two spares I had, but I
haven't had time to open up the amp and see if that was the problem.
If I'm able to get the amp back on line, I'll do the tests. My basic
premise is that ferrite cores are ceramic insulators with some
dielectric loss, and that high VSWR can create a E-field that generates
heat in the core not directly relate to the magnetic flux created by
current in the coil. I could easily be wrong, but it will be
interesting to see.
Take care es 73,
Dave AB7E
On 9/7/2020 12:01 AM, HP wrote:
Got sent by accident -- I would not try this except with a rugged tube amp and
watch it carefully feeding the series resonated case-
The core may heat very rapidly . I had decided to not send it .
I did basically the magnetizing flux portion years ago evaluating Q1 , Q2 Q3
Indiana General rods for a 1.5 KW
antenna loading coil application in the 1.5 to 3. 4 mhz region. Along with
heating we were looking at whether
there were any IMD issues at high levels of amp turns -We did not see any even
at levels that heated the cores so fast
it was a moot point . I also learned to not cool the cores too fast or I had a
lump of useles grey
Hank K7HP
----- On Sep 6, 2020, at 11:48 PM, pfizenmayer <pfizenmayer@q.com> wrote:
| Ok -- here is a suggestion ----- if the question is what is causing the cores
to
| heat ....
| some "electric field" or ampere turns magnetizng flux.
| Make a short piece of bifilar transmission line - parallel or twisted but with
| insulation that will withstand heat -like teflon.
| Make the line it long enough to put some 5 to 10 turns on a subject core. Set
up
| your tx to fed a dummy load with this
| section of line/core in series and run say a Kw or so into the dummy load -
| calculate the current . For this case
| there should be nil amount of ampere turns magnetizng the core. Measure the
core
| temperature after x min or seconds
| Now just disconnect the "ground " side side of the bifilar transmission line
at
| both ends -leave it float and insert a capacitor
| of the values needed in series with the "hot' conductor to series resonate out
| the inductance of that winding and run the same
| power -. See what the temp is after the same X seconds or min .
| ----- On Sep 4, 2020, at 5:04 AM, W4TV Joe Subich <lists@subich.com> wrote:
| Balun/common mode choke what is the difference? Neither
| should be magnetizing the core unless you are talking
| about a magnetically coupled transformer like the isolation
| transformer in an FCP system.
| 73,
| ... Joe, W4TV
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