Hi Riki
I own a 1990 HF-2500 which I got from the estate of a local ham
many years ago. I had a question about it on this forum last week
but through perseverance and much hair pulling, I managed to
resolve it.
Anyway, when I got the amp, there was a spare plate choke with
it. It is different to the one in the amp. It is on a 4" long, 1"
diameter former and it is a single layer coil with a tap point
about 30% up from the bottom and there was a orange 100pF/10kV Z5U
ceramic capacitor which came with the choke. I assume that his
capacitor is connected to that tap on the coil.
I don't need the choke. The one in my amp is fine and if it ever
does go bad, then I would replace it with one of W8JI's chokes,
which I'm sure work work in that location, especially since the
amp does not have 12, 17 and 30m.
I am happy to post it to you for the cost of the postage from
Australia. It would take around 2 weeks to get to you via ordinaly
parcel post. I could also send it express if you wanted it
quicker.
Email me direct at vk6apk@... if you think it would be
suitable. I'm happy to take pics and email them to you direct.
73, Alek VK6APK.
On 30/01/2025 1:26 pm, Riki, K7NJ via
groups.io wrote:
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Somebody who previously owned my Commander HF-2500 replaced
the carbon resistors in the plate parasitic chokes with a
different type of resistor.? This worked fine on low frequencies
160M, 80M, and 40M.? ?When I used the amplifier on 10M, it
became very unstable, most likely with a parasitic oscillation
and caused the plate blocking capacitor to explode and catch on
fire. The main fuses blew, as well as the one on the board that
contains the bias and control circuitry.? After replacing these
fuses and installing carbon resistors in the parasitic
suppressors, I found that the amplifier would no longer work on
80M.? Eventually, I discovered some discolored places on the
plate RF choke where it had evidently arced through its
insulation causing the needed 10M high impedance to shift.? The
choke was replaced? with one I had from another Commander
HF-2500 that has been a source of spare parts.? While trying to
do this, the windings (there's more than one - rather complex
winding - some over the top of others) became loose, and I
unsuccessfully spent several hours trying to get the windings
back like they were and tight on the form they were wound on.?
Even though not satisfied with the replacement choke with loose
and sloppy windings, I tried the amplifier on all the usual
bands starting at 160M and up to 10M.? It seems to work fine up
through 15M, but the 10M band doesn't tune properly - most
likely because the plate choke was still a problem.
?
Does anybody have an original Commander HF-2500 plate choke
that they would like to sell or know where I might find one??
Another possibility is to substitute a different plate choke
that works well in another amplifier with similar plate
parameters. Probably the big challenge in using a different
choke would be to mechanically fit it into the rather crowded
place in the Commander. Another possibility would be to add a
second plate RF choke with a high impedance on 10M in series
with the other choke, but this still might be problematical due
to the tendency of the big choke to break down as before.
Suggestions, especially from anyone who has successfully used a
different choke in the Commander, would be very much
appreciated.
73, Riki K7NJ
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