One procedure to test and adjust a choke is this:
1. Short it in place and check for resonances in the ham bands with a
GDO. The short makes it possible to find series resonances. Leave the
tube and everything else in place (I don't need to add power off and
caps discharged!)
2. If you find any dips within a couple of hundred kHz of a ham band,
remove a turn or two and check again. Don't cut the wire in case you
want to wind it back.
There is probably an easier method with a VNA, but I know this one
works. It can be a little frustrating because when you move the
resonance away from one band, you can easily create one in another.
FWIW I've used the Ameritron choke in several commercial and homebrew
amps with no problems.
73,
Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO
https://www.qsl.net/k2vco/
On 08/11/2021 4:16, John Keating wrote:
Hello again list,
I received a few responses to my last post including and some photos
of the plate choke from the original QRO HR2000 amps. They seem to be
close wound with something like 120 turns on the 1.5" diameter delrin
form, giving about 175uH. I tried winding a few versions like that
and find resonances in the ham bands. I'm wondering how the other
amps work in that condition.
Second, bigger issue, that drove me to investigate the OEM choke
design is that the Ameritron plate chokes I have been using in that
amp burn in their center sections on tune-up key down on 10m. Looking
for suggestions to remedy that problem.
73, John AI6LY _______________________________________________ Amps
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